Our Gemara on Amud Beis records an incident of a woman whose husband was away for twelve months delivered a baby.  Obviously, there ought to be a concern that this child was a mamzer, yet the Gemara rules that it is conceivable that her pregnancy lasted for twelve months, and so the child is kosher.

What I find fascinating about Gemaras such as these is that often we must say Nishtanu HaTibiyyim, the medical and physiological realities have changed (which is a well accepted Halakhic principle, see for example Biur HaGra Choshen Mishpat 331:3:1). Yet, we should never underestimate Chazal’s meticulous attention to detail, and medical history. Since the Gemara is based on case law over centuries, many unusual medical phenomena were recorded, which may have eluded ancient and even modern medical practitioners before careful record keeping was standard. In this case, believe it or not, indeed it is possible for a woman to deliver at twelve months!

According to a Time Magazine article (May 5, 1945), and verified medical records, a woman Beulah Hunter gave birth to a child after 365 days of gestation. See https://content.time.com/time/magazine/article/0,9171,797153,00.html )

While we are on the topic of Talmudic medical anomalies, here is another surprising one from Shabbos 53b:

תָּנוּ רַבָּנַן: מַעֲשֶׂה בְּאֶחָד שֶׁמֵּתָה אִשְׁתּוֹ וְהִנִּיחָה בֵּן לִינַק וְלֹא הָיָה לוֹ שְׂכַר מְנִיקָה לִיתֵּן, וְנַעֲשָׂה לוֹ נֵס וְנִפְתְּחוּ לוֹ דַּדִּין כִּשְׁנֵי דַּדֵּי אִשָּׁה וְהֵנִיק אֶת בְּנוֹ.

The Gemara cites a related baraisa in which the Sages taught: There was an incident where one man’s wife died, and she left him a son to nurse, and he did not have money to pay the wages of a wet-nurse. And a miracle was performed on his behalf, and he developed breasts like the two breasts of a woman, and he nursed his son.

And there is a similar Midrash (Bereishis Rabbah 30:8) about Mordechai who actually nursed Esther when she became orphaned.

Apparently, in rare cases, men can spontaneously lactate, see https://www.scientificamerican.com/article/strange-but-true-males-can-lactate/ )

So the lesson is, never underestimate Chazal.