Niddah 27: Multiple Pregnancies

We learn more about the birth of the placenta today.  Rabban ba Sheila says that Rav Mattana says in the name of Shmuelas that a placenta is considered to be connected to a birth that took place within ten days earlier.  Rabba bar bar Chana quotes Rabbi Yochanan saying that an afterbirth is connected to a birth that took place within twenty-three days earlier.  Rav Yosef said twenty--four days.  Rav Acha ben Rav Avira quoted Rabbi Yitchak saying that he know of a birth of a second child following the first birth after thirty-three (thirty-four, says Rav Yosef) days.  Rabbi Avin bar Adda quotes Rav Menachem ish Kfar She'arim (or Beit She'arim) saying that one incident describes a woman who was pregnant with twins where the birth of the second child took place thirty three days after the first.  This happened to Yehuda and Chizkiyya, the sons of Rabbi Chiyyah.

This contradicts Rav's ruling in yesterday's Mishna.  It also suggests that Rav, Rabbi Chiyya's nephew, did not properly know about the birth of his cousins' births.  Tosafot try to reconcile this by suggesting that Rav knew there were longer times between births but because it was unusual, it should not be used to develop halacha.  The Ran says that Rava's statement applies to situations where both fetuses were fully developed.  If one was not fully develop, it may remain in utero for longer periods of time.

Abaye explains Yehuda and Chizikiyya's births based on a rabbinic idea: normal gestation cycles are either seven or nine months.  Steinsaltz explains that this is not supported by modern science but that superfetation, a double pregnancy where a fetus is formed during an existing pregnancy, exists in rare cases.