Niddah 38 - The Term of Pregnancy
The pious ones of old would cohabit only on Wednesdays, so that their wives would not come to cause desecration of the Sabbath by giving birth on a Sabbath. The normal pregnancy term in either 271 days, 272, or 273, so the birth would occur on Sunday, Monday, or Tuesday. But - asks the Talmud - cohabitation on Thursday, Friday, or the Sabbath also cannot lead to a birth on the Sabbath!? - True, understand "only on Wednesdays" as "from Wednesday onward."
What was the reasoning of the pious ones of old? In the book of Ruth it says, "And God granted her pregnancy." Pregnancy in Hebrew is "Herayon", הריון, with the numerical value of 5+200+10+6+50=271, to allude that the term of pregnancy is 271 days.
After giving birth to a girl, and observing the fourteen days of labor-caused ritual impurity, the woman is pure for the next sixty-six days, even if she sees blood. What happens if she became pregnant at the beginning of these pure days, but then had a miscarriage before they were up? Is the blood of this second childbirth also pure? The Sages says that indeed all her blood during those eighty days is pure. Of course, when she actually delivers a fetus, she has a different ritual impurity - that of giving birth. However, Rabbi Eliezer says that only normal blood is excluded, because it is connected to the first birth, but not this blood, which is connected to the second birth.
Art: Alexander Johnston - Sabbath