Sotah 27 ~ When is a Woman Most Fertile?

Today's daf  has a gynecological theme. The Talmud describes a dispute about when a  woman is most fertile. One opinion is that "a woman only conceives close to her period"  (אין אשה מתעברת אלה סמוך לווסתה), and a second opinion is that "a woman only conceives close to her immersion in a mikvah" (אין אשה מתעברת אלה סמוך לטבילתה).  Today, we will figure out which of these competing medical theories is correct.

Medical students spend many hours learning the hormones whose rise and fall causes ovulation.  But understanding the ovulation cycle is the key to understanding this passage in the Talmud, so let's spend a paragraph on...

Ovulation in women

There are two important hormones that regulate ovulation in a woman. One is called Follicle Stimulation Hormone, or FSH. This is produced in the pituitary gland deep in the brain and it acts on the ovaries to produce follicles, which are little groups of cells that may produce an egg. Under the action of FSH, the ovaries produce many follicles, but usually only one will go on to produce and release an egg. (If more than one follicle releases an egg, and both are fertilized, the result is non-identical twins.)  

A sudden spike in FSH and another hormone called Luteinizing Hormone (LH) causes the winning follicle to release its egg, which floats down the Fallopian tube and into the uterus. If the egg meets a sperm cell, they unite and start down the pathway to producing a baby. But if no sperm cell is encountered, there is a drop in the level of two other critical hormones, progesterone and estrogen (also known as oestrogen for our British readers). This causes the lining of the uterus to slough off, and menstrual bleeding begins, until the whole cycle begins again.

Diagram from here.

Assuming a twenty-eight day cycle, the FSH-LH level peaks just before or around day fourteen, and these hormones trigger ovulation - the release of the egg from the ovaries - soon after.

“Scholars of the ancient world thought that menstruation represented an excess of blood from which the woman must periodically rid herself in order to cleanse her body from noxious substances. Only during the twentieth century has the scientific basis for the menstrual cycle and its hormonal relationships been clarified.”

— Avraham Steinberg. Encyclopedia of Jewish Medical Ethics. Feldehim 2003. Vol II p650.

Counting the Days to Mikveh

As outlined in the Torah (Leviticus 15:19), a menstruating woman is ritually unclean - Niddah - for seven days. After that she undergoes a ritual bathing in a mikveh, and she may resume physical and intimate contact with her husband. However the biblical seven day period was transformed in talmudic and later rabbinic tradition. The result was the addition of another (minimum) of five days to the length of time that a couple must abstain from physical intimacy. As a result, if we assume that day one of the onset of menstruation is the first day of the 28 day average menstrual cycle we discussed above, then the earliest day for a woman to immerse in the mikveh is on day twelve, or two days before ovulation is likely to occur.

The length of the menstrual cycle varies to a remarkable degree among different populations and in different age groups. In women age 19-41 in the US it varies from about 23 to 38 days (with a mean of 31 days.) In Danish women aged 20-35, however, the cycle is about 26-31 days, with a mean of 28 days. And each different cycle length will have its own ovulation day, and each varied ovulation day will affect the day on which conception is most likely.

Cycle length distributions for selected samples from various human populations. The numbers at the far left of each sample identify the corresponding sample and data. From Amy L. Harris & Virginia J. Vitzthum. Darwin's Legacy: An Evolutionary View of Women's Reproductive and Sexual Functioning, The Journal of Sex Research 2013. 50:3-4, 207-246.

The Timing of Sexual Intercourse and the Probability of Conception

The next issue in deciding which of the two opinions in today's page of  Talmud might be correct is this:  on which days around ovulation is a woman most fertile?  This question was addressed in a study published in the esteemed New England Journal of Medicine in 1995. The authors followed 221 healthy woman who were trying to become pregnant (for a total of 625 menstrual cycles!!).  The women kept records of when they had sexual intercourse, and their urine was tested for hormone metabolites to estimate the day of ovulation.  The study found that  "conception occurred only when intercourse took place during a six-day period that ended on the estimated day of ovulation." The authors note that couples who abstain from sexual intercourse until they have evidence of ovulation may miss the opportunity for conception.   

Probability of Conception on Specific Days near the Day of Ovulation.
The bars represent probabilities calculated from data on 129 menstrual cycles in which sexual intercourse was recorded to have occurred on only a single day during the six-day interval ending on the day of ovulation (day 0). The solid line shows daily probabilities based on all 625 cycles, as estimated by a statistical model. From Wilcox A. et al. Timing of sexual intercourse in relation to ovulation. N Engl J Med 1995;333:1517-21.

As you can see in the graph below, the day on which women are most likely to conceive is two to three days before ovulation. This is independent of their age.

Fertile window for four age groups. Probability of conception is highest for an act of intercourse occurring two days prior to ovulation. Redrawn from Dunson et al. (2002). Changes with age in the level and duration of fertility in the menstrual cycle. Human Reproduction, 17(5), 1399–1403, and cited in Amy L. Harris & Virginia J. Vitzthum. Darwin's Legacy: An Evolutionary View of Women's Reproductive and Sexual Functioning, The Journal of Sex Research 2013. 50:3-4, 207-246.

The chances of conception on a random day

In a review of the variability in ovarian function, Amy Harris and Virginia Vitzthum from Indiana University note that although it is the case that the fertile window is fairly narrow (about six days, ending within 24 hours after ovulation) “it does not follow that the fertile window occurs during a narrow range of days during the menstrual cycle. To the contrary, because the timing of ovulation during a cycle is quite variable, women have a 10% or greater probability of being in their fertile window on every day from cycle days 6 through 21, and more than 70% of women are in their fertile window before cycle day 10 or after cycle day 17.”

So they plotted the probability of conception on each cycle day and then calculated the mean probability of conception (i.e., clinical pregnancy following a single act of unprotected intercourse on a random day). What they found was that the average probability during cycle days 7-14 was 25% higher than that during cycle days 14-21. The average probability during the first two weeks of the cycle was 16% higher than that during the next two weeks. “Furthermore, in that subset of women who reported having irregular cycles, a not uncommon pattern, the average probability during cycle days 7-14 is less than half of that during cycle days 14 to 21.”

“Among healthy women trying to conceive, nearly all pregnancies can be attributed to intercourse during a six-day period ending on the day of ovulation. ”

— Wilcox A. et al. Timing of sexual intercourse in relation to ovulation. N Engl J Med 1995;333:1517-21.

Panel A: The probability of ovulation by cycle day. Normal variation in the length of the follicular phase of the menstrual cycle: effect of chronological age.

Panel B: Daily probability of conception on each cycle day; mean probability of conception during cycle days 7 to 14= 6% and during cycle days 14 to 21 = 4.8%

Panel C: Daily probability of conception on each cycle day for women reporting regular cycles (thick line) and for those reporting irregular cycles (thin line); in latter sample, the average probability of conception during cycle days 7 to 14 is 2.5% and during cycle days 14 to 21 it is 5.8%.

Halakhic Infertility

Sometimes, a woman may be biologically fertile, but unable to conceive because of halakhic considerations. If a woman has a menstrual cycle that is shorter than the average 28 days (and about 20% of women have just that), or if a woman bleeds for more than 5 days (resulting in a longer Niddah time, in which the couple may not have intercourse,) then  - and pay attention to this - then ovulation takes place during the Niddah time. And if that happens, as we noted above, then conception is all but impossible. This might be called halakhic infertility, and it is more common than you might have thought.    

In a study of the prevalence of halakhic infertility in a population of ultra-orthodox Jews seeking help from a fertility clinic, a group from Hadassah Hospital in Jerusalem studied 45 infertile women. They found that precoital ovulation was prevalent in one-fifth (21%) of the patients.  "Since not obeying the halachic code of conduct is non-negotiable, and in view of the void of halachic solutions, most couples (68%) seek medical advice and treatment."  Fortunately such treatment is available: taking an an oral estrogen can delay ovulation to after the time of mikveh, and allow intercourse to take place at a time when conception is more likely.  

“A fifth of infertile couples were diagnosed as suffering from infertility due to a religious rather than biological cause...This significant proportion of infertile couples who suffer from sociocultural infertility mandates special attention, primarily of the Rabbinate [sic] authorities.”

— Haimov-Kochman R. et al. Infertility associated with Precoital Ovulation in Observant Jewish Couples; Prevalence, Treatment, Efficacy, and Side Effects. Israel Medical Association Journal 14 (2011): 100-103.

Back to the Daf - Which Opinion is Correct?

Let's now return to the question with which we opened; which of the following two opinions is correct?

1. A woman only conceives close to her period(אין אשה מתעברת אלה סמוך לווסתה).

2. A woman only conceives close to her immersion in a mikvah (אין אשה מתעברת אלה סמוך לטבילתה).

The first opinion is most certainly not supported by modern medicine. The second opinion is often likely to be true, but - and this is a BIG BUT - only for women for whom both the menstrual cycle is not short and menstrual bleeding is not long. For a sizable number of women, conception is no longer possible when they are ready to go to the mikveh.

It is a remarkable fact (and one I have never seen addressed or even acknowledged) that orthodox Jewish practice has evolved to permit intercourse only in that part of the menstrual cycle which has a lower chance of conception. As a result, orthodox Jews have become in this respect, halachically subfertile. Fortunately that doesn’t seem to have made much of a dent in their rates of reproduction. “Being Orthodox” wrote Michelle Shain of the Center for Modern Jewish Studies at Brandeis, “increases the odds of having any births by a factor of 7.18 and, among women who have given birth, increases the expected number of births by a factor of 6.14.” Remarkably, this is in spite of, and not because of, the laws of ritual impurity that are a foundation of Jewish practice.

Mean expected number of births by age, education and Orthodoxy. From Michelle Shain, Understanding the Demographic Challenge: Education, Orthodoxy and the Fertility of American Jews. Contemporary Jewry 2019. 39: 273.

“Consultation with a Rabbinate [sic] authority was reported by 64% of women, but no halachic solution was provided to any of the applicants. ”

— Haimov-Kochman R. et al. Infertility associated with Precoital Ovulation in Observant Jewish Couples; Prevalence, Treatment, Efficacy, and Side Effects. Israel Medical Association Journal 14 (2011): 101.

Berachot 60a ~ Gender Determination

In the time of the Talmud and for centuries beyond, it was very important for a couple to produce male children. To this end, some rabbis suggested a technique to ensure that a boy was produced. Here it is described in today’s page of Talmud:

ברכות ס, א

וא"ר יצחק אשה מזרעת תחלה יולדת זכר איש מזריע תחלה יולדת נקבה

Rabbi Yitzchak said that if the woman emits seed first she gives birth to a male, and if the man emits seed first she gives birth to a female.

Today we will explore the topic of gender determination in the Talmud.

How to conceive a boy or a girl

In the tractate Niddah the statement about “emitting seed first” comes up several times, and in the name of a few different rabbis. And, as if emphasize its importance, the Talmud offers no fewer than four different supporting proofs for the principal. The first is the one that we just read in the name of Rav Ami:

נדה לא, א

אמר רבי יצחק אמר רבי אמי אשה מזרעת תחילה יולדת זכר איש מזריע תחילה יולדת נקבה שנאמר (ויקרא יג, כט) אשה כי תזריע וילדה זכר 

Rabbi Yitzchak says that Rabbi Ami says:The sex of a fetus is determined at the moment of conception. If the woman emits seed first, she gives birth to a male, and if the man emits seed first, she gives birth to a female, as it is stated: “If a woman bears seed and gives birth to a male”(Leviticus 12:2). 

The suggestion from the verse is that “if a woman bears seed” first, then she will “give birth to a male.” A second proof text from the Torah is provided by Rabbi Tzadok, this time from the story of our matriarch Leah.

תנו רבנן בראשונה היו אומרים אשה מזרעת תחילה יולדת זכר איש מזריע תחלה יולדת נקבה ולא פירשו חכמים את הדבר עד שבא רבי צדוק ופירשו (בראשית מו, טו) אלה בני לאה אשר ילדה ליעקב בפדן ארם ואת דינה בתו תלה הזכרים בנקבות ונקבות בזכרים 

The Sages taught: At first, people would say that if the woman emits seed first she gives birth to a male, and if the man emits seed first, she gives birth to a female. But the Sages did not explain from which verse this matter is derived, until Rabbi Tzadok came and explained that it is derived from the following verse: “These are the sons of Leah, whom she bore to Jacob in Paddan Aram, with his daughter Dinah”(Genesis 46:15). From the fact that the verse attributes the males to the females, as the males are called: “The sons of Leah,” and it attributes the females to the males, in that Dinah is called: “His daughter,” it is derived that if the woman emits seed first she gives birth to a male, whereas if the man emits seed first, she bears a female.

בנדה לא ,א–ב

The Talmud brings a third proof text, this one from the Book of Chronicles:

ויהיו בני אולם אנשים גבורי חיל דורכי קשת ומרבים בנים ובני בנים וכי בידו של אדם להרבות בנים ובני בנים אלא מתוך שמשהין עצמן בבטן כדי שיזריעו נשותיהן תחלה שיהו בניהם זכרים מעלה עליהן הכתוב כאילו הם מרבים בנים ובני בנים והיינו דאמר רב קטינא יכולני לעשות כל בני זכרים 

“And the sons of Ulam were mighty men of valor, archers, and had many sons and sons’ sons”(I Chronicles 8:40). Is it in a person’s power to have many sons and sons’ sons? Rather, because they delay while lying on wives’ abdomen, initially refraining from emitting semen so that their wives will emit seed first, in order that their children will be male, the verse ascribes them credit as though they have many sons and sons’ sons. And this statement is the same as that which Rav Ketina said: I could have made all of my children males,by refraining from emitting seed until my wife emitted seed first. 

And finally, the fourth proof text. A later passage in Niddah (Niddah 70b-71a) cites a number of questions that the sages of Alexandria asked of Rabbi Yehoshua. One of them was how can a man ensure he has male children? Rabbi Yehoshua told them the man should do two things: marry a woman who is fit for him, and act modestly during sexual intercourse. Hold on, the sages of Alexandria replied. Many men have done that, and it didn’t help! Rabbi Yehoshua then qualified his answer, and explained that in addition to marrying an appropriate woman and being modest, a man needs to pray for a son. Rabbi Yehoshua then cited a proof text from Psalms (127:3):

הנה נחלת ה' בנים שכר פרי הבטן

Behold, children are a heritage of the Lord; the fruit of the womb is a reward

So far so good. To have male children a man needs to marry an appropriate wife, act modestly when he is intimate with her, and pray. But now the Talmud asks a question based on the proof text. What is the act for which the reward are children?

א"ר חמא ברבי חנינא בשכר שמשהין עצמן בבטן כדי שתזריע אשתו תחילה נותן לו הקב"ה שכר פרי הבטן

Rabbi Chama, son of Rabbi Chanina, says: In reward for men withholding their semen in their belly in order to allow their wives to emit seed first, the Holy One, Blessed be He, gives him the reward of the fruit of the womb, [that is, sons].

These are the four different proof texts from the Bible to support the claim that if a woman emits her seed first, she will give birth to a boy. Of course now we need to determine what, precisely, is meant by the phrase “if the woman emits seed first” (מזרעת תחילה).

Understanding THE PHRASE

(i) Ovulation

Perhaps it could refer to ovulation. This makes sense to us since we understand that fertilization requires two “seeds,” the egg, and sperm. But this would not have made sense to the rabbis of the Talmud. They, like everyone else at the time (and indeed until the beginning of the seventeenth century) had no concept of mammalian ovulation. In fact it was the blood that was lost at menstruation that was believed to be the mother’s contribution to her child’s formation, and not any eggs she may produce.

A classic example of this lack of understanding of ovulation is found in the early medieval commentary of Moses ben Nachman, known as Ramban (1194–1270) to Leviticus 12:2. Here is the key bit:

כי האשה אע"פ שיש לה ביצים כביצי זכר או שלא יעשה בהן זרע כלל או שאין הזרע ההוא נקפא ולא עושה דבר בעובר

For even though a woman has ovaries like the testes of a man, either they do not produce eggs at all, or else the egg jells and contributes nothing to the fetus.

(ii) Orgasm

The other possibility is that “emitting seed first” refers to orgasm. If you want to have a boy, the rabbis said, the husband should allow his wife to have an orgasm before himself. This interpretation is favored by the historian of all things medical and talmudic, Fred Rosner. Here is what he wrote in Medicine in the Bible and The Talmud (Ktav Publishing and Yeshiva University Press 1977, p175):

It seems obvious…that the meaning must be orgasm rather than ovulation, for otherwise it would not make sense to speak of the men restraining themselves during intercourse in order to allow their wives to “emit seed” first.

Theories of sex determination in Antiquity

In a fascinating paper in the Journal for the Study of Judaism, the scholar Pieter van Horst wrote “it is certain that ancient Greek concepts of embryogenesis influenced Jewish theories about the coming-into-being of a foetus.” So let’s look at some of those theories.

Aristotle (384–322 BCE) recorded the belief (with which he did not agree) that male offspring come from the right side of the male and females from the left side; an embryo that develops in the “right side” of the uterus (whatever that means) becomes male while that which develops in the left side becomes female. Aristotle himself believed that the mother’s contribution to the fetus was menstrual blood, and it had the same origin as male semen, although it was not as developed.

Another Greek, Empedocles (c. 494-434 BCE) thought that “heat” (whatever that means) gave rise to males and cold to females. But the view in the Talmud about editing seed first can be traced further back to another Greek, Democritus of Abdera (c. 460 - c. 370 BCE). Democritus believed that the gender depended on the parent whose semen predominated, “not the whole of the semen, but that which has come from the part by which male and female differ from one another.”

By the time we get to Galen, the Greek physician of the second century, there was an acknowledgement that the mother contributed her own seed, but, as van Horst notes the thought was that“…female sperm is by far less perfect, thinner, and colder than male sperm; it serves only as food for the male semen in its development into an embryo.

“The material surveyed so far covers the period of roughly 500 B.C.E. to 200 C.E. It has shown us that throughout this period a theory about female semen had its place side by side with a theory that denied females a contribution to embryogenesis. ”

— Pieter W. van Horst. Bitenosh's Orgasm. Journal for the Study of Judaism 2012. 43: 613-628.

A new understanding of a Dead Sea Scroll

It is with this background that van Hort explains an enigmatic passage in one of the Dead Sea Scrolls (1QapGen2:9-15), known as the Genesis Apocryphon. It is one of the original Dead Sea Scrolls discovered by Bedouin shepherds in 1946 and now held at The Shrine of the Book in Jerusalem.The scroll recounts a discussion between Noah and his father Lemech, who was worried that Noah was not really his own progeny. “I thought in my heart” says Lemech, “that the conception was the work of the Watchers, and the pregnancy of the Holy Ones, and it belonged to the Nephilim.” He suspects that his wife Bitenosh has committed adultery.

Then Bitenosh, my wife, spoke to me very harshly... (9) and said: 'Oh my brother and lord, remember my sexual pleasure!... (10) in the heat of intercourse, and the gasping of my breath in my breast.'" …(14) Remember my sexual pleasure!... (15) that this seed comes from you, that this pregnancy comes from you…

How, asks van Horst, could Bitenosh think that a reference to the pleasure she experienced when being intimate with Lamech would allay his suspicion? And here is his fascinating solution:

That could only be a convincing argument if that pleasure entailed the conception of their child at the moment the two of them (and no one else) were together. Since the author implies that Bitenosh's argument did convince Lamech, he must have meant her reference to her pleasure to be a conclusive argument. So "pleasure" must here definitely be something much more specific than just the fact that Bitenosh had a pleasant time with Lamech when they begot Noab. That is to say, most probably Bitenosh here refers to her orgasm on that occasion. The fact that not only Lamech but also Bitenosh had an orgasm at that moment is taken as a proof that it is the two of them, together who begot the child. That can only be the case if the female orgasm is here regarded as the event during which she emitted her own seed into her womb where it mingled with Lamech's seed so as to form the beginning embryo. It is only a double-seed theory that can explain why Bitenosh here takes recourse to an appeal to her moment suprême (to which Lamech was witness!) as a cogent argument…

It is fascinating to see how an originally Greek scientific concept here serves to allay the anxious suspicions of a biblical hero.

Yes. It is.

It wasn’t until the invention of the microscope and the work of Antonie van Leeuwenhoek (1632-1723) and Reinier de Graaf (1641-1673), that we began to understand what was really going on. The former described seeing sperm in semen, and the latter dissected pregnant rabbits and described the development of the egg in the ovary. (Fun fact: in his honor, the structure within which the egg matures is known to this day as a Graafian follicle.)

Other ways to have a baby boy

The scholar Moses Gastner who died in 1939 was a lifelong collector of Hebrew manuscripts. These later became part of the collectionso of both the Rylands Library in Manchester and the British Library in London. Gastner also translated the siddur, wrote a history of the Bible, and led the Spanish and Portuguese Congregation in London. Among his many works was a little-known entry (“Birth, Jewish”) in the two-volume Encyclopædia of Religion and Ethics published in New York in 1908. In the entry Gastner included material from his the vast collection of medical and magical manuscripts. Here is one, which Gastner does not date: 

If a woman is anxious to get sons, she must ask a shepherd to get the after-birth of a cow, dry it, and pound it, and drink the powder in wine.

If dried cow after-birth did not suit your tastes, there was this: 

Make a decoration of bear’s or wolf’s meat as much as a bean. If the animal is male the child will be male, and if it is female, the woman will give birth to a daughter.

The Talmud (Niddah 31b) suggested another, perhaps more palatable method to guarantee a baby boy:

אמר רבא הרוצה לעשות כל בניו זכרים יבעול וישנה 

Rava said: One who wishes to make all of his children males should engage in intercourse with his wife and repeat the act.

It’s not a secret any more

At the conclusion of his article on sex determination in the Talmud, Rosner wrote that the Talmud 

emphatically states that if a woman emits her semen first, she will bear a male, and if the man emits his semen first, she will bear a female. We have yet to understand what the Talmud means. The secret of sex predetermination remains hidden.

But this is not correct. We certainly do understand what the Talmud meant, where that meaning came from and what became of it. What once was certainly a mystery (but not a secret) is now well understood. The gender of offspring is determined by chromosomes, and nothing else. 

What actually determines the gender of a fetus

A human egg or sperm each contain 23 chromosomes. All eggs carry an X chromosome; each sperm carries an X or a Y chromosome. If a sperm with an X chromosome fertilizes the egg, the fetus grows into an XX female. If a sperm with an Y chromosome fertilizes the egg, the fetus grows into an XY male. That’s it. Simple.

[Reprint from Niddah 28a].

Niddah 30-31 ~ Talmudic Obstetrics

Let’s go back to some of the Talmud we studied last week in the daf yomi one-page-a-day cycle, and catch up with some topics we didn’t have a chance to cover.

1. Which fetus grows quicker, Male or Female? (The male)

In the Mishnah (30a) there is a dispute between Rabbi Yishmael and the rabbis about the length of time it takes for a fetus to reach a milestone of completion.

רבי ישמעאל אומר יום מ"א תשב לזכר ולנדה יום פ"א תשב לזכר ולנקבה ולנדה שהזכר נגמר למ"א והנקבה לפ"א וחכ"א אחד בריית הזכר ואחד בריית הנקבה זה וזה מ"א

Rabbi Yishmael said…the formation of the male offspring concludes on the forty-first day and the formation of the female offspring concludes on the eighty-first day. And the Rabbis say: both a male and female fetus concludes on the forty-first day.

In one respect, both the rabbis and Rabbi Yishmael were incorrect: the fetus is not fully formed, or fully anything by the forty (ot the forty-first day). Here is what a human embryo looks like at about four weeks (28 days), six weeks (42 days) and seven weeks (49 days). Does one stage look any more “complete” than another?

Human embryo at about 28 days.

Human embryo at about 40 days. It is about 11mm long.

Human embryo at about 46 days. All images are from From Nilsson, Lennart. A Child is Born. Delacorte Press/Seymour Lawrence. 1990.

But in another respect Rabbi Yishmael was certainly correct and the rabbis were wrong: the male and female fetus do grow at different rates. Back in the late 1960s scientists suggested that the greater the antigenic differences between mother and fetus, the greater is the fetal growth rate. In other words an (XY) male fetus grows at a quicker rate than a (XX) female fetus because an XY fetus is more different from its XX mother than is an XX fetus.

It is well known that, on average, boys weigh slightly more than girls at birth. Less known is the fact that when in utero, boys grow at a quicker rate than girls. For example the diameter of the fetal head (called the biparietal diameter) is larger in male fetuses than in the female, and this difference becomes statistically significant at 24 weeks. Head circumference is also larger for males and becomes significantly greater than that of the female fetus at 24 weeks' gestation.

Head circumference (centimeters) as a function of gestational length (weeks) in both male (•) and female (o) fetuses. From Parker A et al. The ultrasound estimation of sex-related variations of intrauterine growth. Am. J. Obstet. Gynecol 1984. 149:665-669.

To conclude: the evidence supports Rabbi Yishmael to the degree that later in utero boys do grow at a slightly quicker rate. However, there is no difference between growth rates before about 24 weeks, and certainly at a forty day cut-off both male and female fetuses are identical. With a generous reading, that supports the opinion of the rabbis.

Very much related to this topic is the story told on the same page of Talmud about Cleopatra and her cruel experiments on young women.

נדה ל, ב

אמרו לו לר' ישמעאל מעשה בקליאופטרא מלכת אלכסנדרוס שנתחייבו שפחותיה הריגה למלכות ובדקן ומצאן זה וזה למ"א אמר להן אני מביא לכם ראייה מן התורה ואתם מביאין לי ראייה מן השוטים 

They said to Rabbi Yishmael: There was an incident involving Cleopatra, Queen of Alexandria. Since her maidservants were sentenced to death by the government, she took advantage of the opportunity and experimented on them to determine the amount of time it takes for an embryo to develop. She had her maidservants engage in intercourse and operated on them following their execution in order to determine the stage at which an embryo is fully formed, and found that both in this case, when the embryo is male, and that case, when it is female, the formation is complete on the forty-first day after conception. Rabbi Yishmael said to them in response: I bring you proof from the Torah, and you bring me proof from the fools?

Not really. A forty day male and a forty female embryo are visually indistinguishable. The reproductive tract begins to develop in the sixth week of the embryonic period, and external genitalia develop during the 8th-14th weeks of gestation. However, external determination of sex is not possible before urogenital modeling is complete, which also occurs between the 8th and 14th weeks. In the hands of an expert ultrasound operator, sonographic determination of fetal sex has been reported as early as 11 weeks’ menstrual age, “but it may be obtained reliably only as early as 12 to 13 weeks.” (The challenge is distinguishing “between a small penis and a prominent clitoris and between minimally edematous labia and a small scrotum filled with spongy connective tissue.” Now you know.)

In the course of a series of challenges to the opinion of Rabbi Yishmael, the Talmud cites the forth century sage Abaye. He suggests that by examining certain of their anatomical characteristics we can determine if two fetuses were a similar age (“אמר אביי בסימניהון שוין”).  He does not define those “characteristics” but Rashi, the eleventh century commentator does.

בסימניהון שוין - נקבה שנמצא ליום פ"א לא היו אבריה ושערה וצפורניה אלא כשיעור של זכר ליום מ"א

Identical characteristics: The limbs, hair, and nails of an 81 day-old female fetus are as developed as those of a 41 day-old male fetus.

There is a problem here. Fingernails only begin to start to develop around day 70 and toenails around day 100. Neither are present at day 40. Hair develops between weeks 7-12. So the claim that either was clearly present in a 40 or 80 day embryo is not possible.

2. How does the uterus grow?(It stretches)

נדה לא, א

תנו רבנן שלשה חדשים הראשונים ולד דר במדור התחתון אמצעיים ולד דר במדור האמצעי אחרונים ולד דר במדור העליון וכיון שהגיע זמנו לצאת מתהפך ויוצא וזהו חבלי אשה 

The Sages taught in a baraita: During the first three months of pregnancy, the fetus resides in the lower compartment of the womb; in the middle three months, the fetus resides in the middle compartment; and during the last three months of pregnancy the fetus resides in the upper compartment. And once its time to emerge arrives, it turns upside down and emerges; and this is what causes labor pains…

Here is what actually happens. The fetus does not occupy different parts of the uterus as it grow. Instead, the uterus itself expands to accommodate the fetus. In a woman who has never been pregnant, the uterus is about 7-8cm long, around the size of a fist. It grows as the fetus develops, reaching up into the abdominal cavity. At 24 weeks’ gestation, the top of the uterus is at the approximate height of the umbilicus, and by the end of pregnancy it may be felt a little below the lower end of the breast bone.

In contrast, the Talmudic description of the baby turning is correct. The baby floats in a heads-up position until the very last couple of weeks of the pregnancy, when it does a 180 degree flip. About 4% of babies refuse to undertake these gymnastics, and remain heads-up, in what is called a breech presentation.

3. who causes worse labor pains, boys or girls?(They are equal OFFENDERS)

נדה לא, א

היינו דתנן חבלי של נקבה מרובין משל זכר 

 The labor pains experienced by a woman who gives birth to a female are greater than those experienced by a woman who gives birth to a male…

…מאי שנא חבלי נקבה מרובין משל זכר זה בא כדרך תשמישו וזה בא כדרך תשמישו זו הופכת פניה וזה אין הופך פניו 

…The Gemara asks: What is different about the labor pains experienced by a woman who gives birth to a female, that they are greater than those experienced by a woman who gives birth to a male?The Gemara answers: This one, a male fetus, emerges in the manner in which it engages in intercourse. Just as a male engages in intercourse facing downward, so too, it is born while facing down. And that one, a female fetus, emerges in the manner in which it engages in intercourse,i.e., facing upward. Consequently, that one, a female fetus, turns its face around before it is born, but this one, a male fetus, does not turn its face around before it is born.

It wasn’t just the rabbis of the Talmud who believed girls caused their mothers more pain during childbirth. Here is Aristotle (d. 322 BCE), in his Historia Animalum (Book 7 Chapter 4):

As a general rule women who are pregnant of a male child escape comparatively easily and retain a comparatively healthy look, but it is otherwise with those whose infant is female; for these latter look as a rule paler and suffer more pain…nevertheless the rule is subject to exceptions.

LEFT: Face down (OA) presentation. Right: Face up (OP) presentation. From here.

When a baby is born face down, that is to day facing the mother’s back, it is said to be in the occipital anterior (OA) position. This is the most common presentation. When the baby is born face up, that is to say facing the mother’s front, it is said to be in the occipital posterior (OP) position. That presentation is less common. In 2005 a group from the Departments of Obstetrics and Gynecology at the Brigham and Women’s Hospital and Boston Medical Center conducted a prospective cohort study of 1,562 women to evaluate changes in baby’s position during labor. They reported that 80% of the babies were delivered OA, 8% were OP and 12% were in the in-between transverse position. Now what about the Talmud’s suggestion that girls are not born face down, or as an obstetrician would say, in the OA position, but rather face up? Take a look for yourself at the results of the study:

Demographic and Pregnancy Characteristics of 1,572 births. From Lieberman E. Davidson K, Lee-Parritz A. Shearer E. Changes in Fetal Position During Labor and Their Association With Epidural Analgesia. Obstetrics & Gynecology 2005. 105 (1): 974-982.

As you can see, boys made up 58% of the face down births and only 49% of the face up births. So although the Talmud’s suggestion that all boys are born face down is not correct, it is certainly the case that slightly more boys than girls are born in this presentation, at least according to this study. However a 2017 Israeli study (which looked at babies with large heads) found that boys made up 51% of the face down births, and 49% of the face up births, which was a statistical wash.

What about pain? If the Talmud is correct, then the face-up (supposedly female) presentation should be more painful than the face-down (supposedly male) one. Is it? Well, no. The Boston study found that mothers face up baby at delivery did not report more painful labors. They had a mean pain score of 4.9 out of 10, compared with 5.2 for other positions - a non statistical difference.

4. Is intercourse during pregnancy harmful?(No)

נדה לא, א

תנו רבנן שלשה חדשים הראשונים תשמיש קשה לאשה וגם קשה לולד אמצעיים קשה לאשה ויפה לולד אחרונים יפה לאשה ויפה לולד שמתוך כך נמצא הולד מלובן ומזורז 

The Sages taught in a baraita: During the first three months of pregnancy, sexual intercourse is difficult and harmful for the woman and is also difficult for the offspring. During the middle three months, intercourse is difficult for the woman but is beneficial for the offspring. During the last three months, sexual intercourse is beneficial for the woman and beneficial for the offspring; as a result of it the offspring is found to be strong and fair skinned.

תנא המשמש מטתו ליום תשעים כאילו שופך דמים מנא ידע אלא אמר אביי משמש והולך (תהלים קטז, ו) ושומר פתאים ה' 

The Sages taught in a baraita: With regard to one who engages in intercourse with his wife on the ninetieth day of her pregnancy, it is as though he spills her blood.The Gemara asks: How does one know that it is the ninetieth day of her pregnancy? Rather, Abaye says: One should go ahead and engage in intercourse with his wife even if it might be the ninetieth day, and rely on God to prevent any ensuing harm, as the verse states: “The Lord preserves the simple” (Psalms 116:6).

Contrary to the Talmud’s assertion, there is no association with the frequency of intercourse during pregnancy and the danger of a miscarriage. Here is what the Mayo Clinic tells patients:

Your developing baby is protected by the amniotic fluid in your uterus, as well as by the strong muscles of the uterus itself. Sexual activity won't affect your baby, as long as you don't have complications such as preterm labor or placenta problems…

Having sex during pregnancy won't provoke a miscarriage. Most miscarriages occur because the fetus isn't developing normally.

“יש ניהגיס כשנכנסה אשתו בחדש ט׳ לעיבורה לעשות בחדש ההוא מצות פתיחת ההיכל והוא מנהג יפה

There is a custom during the ninth month a woman’s pregnancy to give her husband the mitzvah of opening the ark. And this is a good custom”

— כף היים ס ׳ קלד, יב By Rabbi Yaakov Chaim Sofer, (1870-1939).

You may have heard about a Jewish folk remedy (a segulah) believed to help start the process of labor in a woman ready to give birth. It is to give her husband the honor of opening the ark during the service in the synagogue. I am not aware of any randomized clinical trial of the belief, but there have been randomized trials of another claim, this one perhaps a little more widespread. That claim is that intercourse late in pregnancy will induce labor.

It goes way back to Aristotle in the fourth century BCE, who wrote that “women who have a connection with their husbands shortly before childbirth are delivered all the more quickly.” However Soranus, another Greek physician who lived in the third century CE (and about 500 years after Aristotle) believed that any intercourse during pregnancy was harmful. Here is what he wrote in his textbook of gynecology:

Sexual intercourse however is always harmful to pregnant women both on account of the tossing motion and because the uterus is forced to submit to a movement which is contrary to the progress of pregnancy. And even more so in the last months lest because of it the chorion burst and the fluid which has been prepared for use in parturition be evacuated before the proper time.

“It is important to find a scientific answer to this issue” wrote a team of researchers in Portugal, “because if it is proven to be true, a decrease in the number of medical interventions for post-term pregnancy can occur.” So they randomized pregnant women to two groups: “vaginal intercourse at least twice a week or abstinence.” Yes, you read that correctly. 63 women and their lucky partners were assigned to the intervention group and 60 to the control. And there were no significant differences between the rates of spontaneous onset of labor in the two groups. A 2019 review from the School of Medicine in Naples Italy concluded that “in women with singleton [i.e. not twins], cephalic [head down], low-risk pregnancies, sexual intercourse at term does not significantly increase the incidence of spontaneous onset of labor.” So that myth is now officially busted.

Next time, on Talmudology: The Zov and Gonorrhea.

Niddah 31a ~ When is a Woman Most Fertile?

Today's daf stays with the theme of gynecology. The Talmud describes a dispute about when a  woman is most fertile. One opinion is that "a woman only conceives close to her period"  (אין אשה מתעברת אלה סמוך לווסתה), and a second opinion is that "a woman only conceives close to her immersion in a mikvah" (אין אשה מתעברת אלה סמוך לטבילתה).  

Medical students spend many hours learning the hormones whose rise and fall causes ovulation.  But understanding the ovulation cycle is the key to understanding this passage in the Talmud, so let's spend a paragraph on...

Ovulation in Humans

There are two important hormones that regulate ovulation in a human. One is called Follicle Stimulation Hormone, or FSH. This is produced in the pituitary gland deep in the brain and it acts on the ovaries to produce follicles, which are little groups of cells that may produce an egg. Under the action of FSH, the ovaries produce many follicles, but usually only one will go on to produce and release an egg. (If more than one follicle releases and egg, and both are fertilized, the result is non-identical twins.)  

A sudden spike in FSH and another hormone called Luteinizing Hormone (LH) cause the winning follicle to release its egg, which floats down the Fallopian Tube and into the uterus. If the egg meets a sperm cell, they unite and start down the pathway to producing a baby. But if no sperm cell is encountered, there is a drop in the level of two other critical hormones, progesterone and estrogen (also known as oestrogen for our British readers). This causes the lining of the uterus to slough off, and menstrual bleeding begins, until the whole cycle begins again.

Diagram from here.

Assuming a twenty-eight day cycle, the FSH-LH peak that trigger ovulation just before or around day fourteen, and ovulation - the release of the egg from the ovaries - occurs soon after.

“Scholars of the ancient world thought that menstruation represented an excess of blood from which the woman must periodically rid herself in order to cleanse her body from noxious substances. Only during the twentieth century has the scientific basis for the menstrual cycle and its hormonal relationships been clarified.”

— Avraham Steinberg. Encyclopedia of Jewish Medical Ethics. Feldehim 2003. Vol II p650.

Counting the Days to Mikveh

As outlined in the Torah (Leviticus 15:19), a menstruating woman is ritually unclean - Niddah - for seven days. After that she undergoes a ritual bathing in a mikveh, and she may resume physical and intimate contact with her husband. However the biblical seven day period was transformed in talmudic and later rabbinic tradition. The result was the addition of another (minimum) of five days to the length of time that a couple must abstain from physical intimacy. As a result, if we assume that day one of the onset of menstruation is the first day of the 28 day average menstrual cycle we discussed above, then the earliest day for a woman to immerse in the mikveh is on day twelve, or two days before ovulation is likely to occur.

The length of the menstrual cycle varies to a remarkable degree among different populations and in different age groups. In women age 19-41 in the US it varies from about 23 to 38 days (with a mean of 31 days.) In Danish women aged 20-35 however, the cycle is about 26-31 days, with a mean of 28 days. And each different cycle length will have its own ovulation day, and each varied ovulation day will effect the day on which conception is most likely.

Cycle length distributions for selected samples from various human populations. The numbers at the far left of each sample identify the corresponding sample and data. From Amy L. Harris & Virginia J. Vitzthum. Darwin's Legacy: An Evolutionary View of Women's Reproductive and Sexual Functioning, The Journal of Sex Research 2013. 50:3-4, 207-246.

The Timing of Sexual Intercourse and the Probability of Conception

The next issue in deciding which of the two opinions in today's page of  Talmud might be correct is this:  on which days around ovulation is a woman most fertile?  This question was addressed in a study published in the esteemed New England Journal of Medicine in 1995. The authors followed 221 healthy woman who were trying to become pregnant (for a total of 625 menstrual cycles!!).  The women kept records of when they had sexual intercourse, and their urine was tested for hormone metabolites to estimate the day of ovulation.  The study found that  "conception occurred only when intercourse took place during a six-day period that ended on the estimated day of ovulation." The authors note that couples who abstain from sexual intercourse until they have evidence of ovulation may miss the opportunity for conception.   

Probability of Conception on Specific Days near the Day of Ovulation.
The bars represent probabilities calculated from data on 129 menstrual cycles in which sexual intercourse was recorded to have occurred on only a single day during the six-day interval ending on the day of ovulation (day 0). The solid line shows daily probabilities based on all 625 cycles, as estimated by a statistical model. From Wilcox A. et al. Timing of sexual intercourse in relation to ovulation. N Engl J Med 1995;333:1517-21.

As you can see in the graph below, the day on which women are most likely to conceive is two to three days before ovulation. This is independent of their age.

Fertile window for four age groups. Probability of conception is highest for an act of intercourse occurring two days prior to ovulation. Redrawn from Dunson et al. (2002). Changes with age in the level and duration of fertility in the menstrual cycle. Human Reproduction, 17(5), 1399–1403, and cited in Amy L. Harris & Virginia J. Vitzthum. Darwin's Legacy: An Evolutionary View of Women's Reproductive and Sexual Functioning, The Journal of Sex Research 2013. 50:3-4, 207-246.

The chances of conception on a random day

In a review of the variability in ovarian function, Amy Harris and Virginia Vitzthum from Indiana University note that although it is the case that the fertile window is fairly narrow (about six days, ending within 24 hours after ovulation) “it does not follow that the fertile window occurs during a narrow range of days during the menstrual cycle. To the contrary, because the timing of ovulation during a cycle is quite variable, women have a 10% or greater probability of being in their fertile window on every day from cycle days 6 through 21, and more than 70% of women are in their fertile window before cycle day 10 or after cycle day 17.”

So they plotted the probability of conception on each cycle day then calculated the mean probability of conception (i.e., clinical pregnancy following a single act of unprotected intercourse on a random day. What they found was that the average probability during cycle days 7-14 was 25% higher than that during cycle days 14-21. The average probability during the first two weeks of the cycle was 16% higher than that during the next two weeks. “Furthermore, in that subset of women who reported having irregular cycles, a not uncommon pattern, length and menses duration), the average probability during cycle days 7-14 is less than half of that during cycle days 14 to 21.”

“Among healthy women trying to conceive, nearly all pregnancies can be attributed to intercourse during a six-day period ending on the day of ovulation. ”

— Wilcox A. et al. Timing of sexual intercourse in relation to ovulation. N Engl J Med 1995;333:1517-21.

This is important.

Panel A: The probability of ovulation by cycle day. Normal variation in the length of the follicular phase of the menstrual cycle: effect of chronological age.

Panel B: Daily probability of conception on each cycle day; mean probability of conception during cycle days 7 to 14= 6% and during cycle days 14 to 21 = 4.8%

Panel C: Daily probability of conception on each cycle day for women reporting regular cycles (thick line) and for those reporting irregular cycles (thin line); in latter sample, the average probability of conception during cycle days 7 to 14 is 2.5% and during cycle days 14 to 21 it is 5.8%.

Halakhic Infertility

Sometimes, as woman may be biologically fertile, but unable to conceive because of halakhic considerations. If a woman has a menstrual cycle that is shorter than the average 28 days (and about 20% of women have just that), or if a woman bleeds for more than 5 days (resulting in a longer Niddah time, in which the couple may not have intercourse) then  - and pay attention to this - then ovulation takes place during the Niddah time. And if that happens, as we noted above, then conception is all but impossible. This might be called halakhic infertility, and it is more common than you might have thought.    

In a study of the prevalence of halakhic infertility in a population of ultra-orthodox Jews seeking help from a fertility clinic, a group from Hadassah Hospital in Jerusalem studied 45 infertile women.  They found that precoital ovulation was prevalent in one-fifth (21%) of the patients.  "Since not obeying the halachic code of conduct is non-negotiable, and in view of the void of halachic solutions, most couples (68%) seek medical advice and treatment."  Fortunately such treatment is available: taking an an oral estrogen can delay ovulation to after the time of mikveh, and allow intercourse to take place at a time when conception is more likely.  

“A fifth of infertile couples were diagnosed as suffering from infertility due to a religious rather than biological cause...This significant proportion of infertile couples who suffer from sociocultural infertility mandates special attention, primarily of the Rabbinate [sic] authorities.”

— Haimov-Kochman R. et al. Infertility associated with Precoital Ovulation in Observant Jewish Couples; Prevalence, Treatment, Efficacy, and Side Effects. Israel Medical Association Journal 14 (2011): 100-103.

Back to the Daf - Which Opinion is Correct?

Let's now return to the question with which we opened; which of the following two opinions is correct?

1. A woman only conceives close to her period(אין אשה מתעברת אלה סמוך לווסתה).

2. A woman only conceives close to her immersion in a mikvah (אין אשה מתעברת אלה סמוך לטבילתה).

The first opinion is most certainly not supported by modern medicine. The second opinion is often likely to be true, but - and this is a BIG BUT - only for women for whom both the menstrual cycle is not short and menstrual bleeding is not long. For a sizable number of women, conception is no longer possible when they are ready to go to the mikveh.

It is a remarkable fact (and one I have never seen addressed or even acknowledged) that orthodox Jewish practice has evolved to permit intercourse only in that part of the menstrual cycle which has a lower chance of conception. As a result, orthodox Jews have become in this respect, halachically subfertile. Fortunately that doesn’t seem to have made much of a dent in their rates of reproduction. “Being Orthodox” wrote Michelle Shain of the Center for Modern Jewish Studies at Brandeis, '“ increases the odds of having any births by a factor of 7.18 and, among women who have given birth, increases the expected number of births by a factor of 6.14.” Remarkably, this is in spite of, and not because of, the laws of ritual impurity that are a foundation of Jewish practice.

Mean expected number of births by age, education and Orthodoxy. From Michelle Shain, Understanding the Demographic Challenge: Education, Orthodoxy and the Fertility of American Jews. Contemporary Jewry 2019. 39: 273.

“Consultation with a Rabbinate [sic] authority was reported by 64% of women, but no halachic solution was provided to any of the applicants. ”

— Haimov-Kochman R. et al. Infertility associated with Precoital Ovulation in Observant Jewish Couples; Prevalence, Treatment, Efficacy, and Side Effects. Israel Medical Association Journal 14 (2011): 101.