I don’t think using weeks was anything other than following regular practice. Example: https://en.wikipedia.org/wiki/Pregnancy https://en.wikipedia.org/wiki/Pre

I don’t think using weeks was anything other than following regular practice. Example: https://en.wikipedia.org/wiki/Pregnancy https://en.wikipedia.org/wiki/Pregnancy: “Childbirth typically occurs around 40 weeks from the start of the last menstrual period (LMP), a span known as the gestational age. This is just over nine months. Counting by fertilization age, the length is about 38 weeks.” I think that’s because months vary in length, making it relatively hard for people to count with them. Example: 28 weeks isn’t 7 months, it is slightly less than 6½ average months (6 months is a tiny bit over 26 weeks, and two weeks under half an average month)