This convention is news to me - though the confusion is not. Months are plain old calendar months in pregnancy (ie about 4.3 weeks).
https://www.verywellfamily.com/how-many-months-pregnant-am-i...
40 weeks is by convention from estimated last menstrual period, which is of course about 2 weeks prior to fertilization - so the actual gestastional period is closer to 38 weeks (that is closer to 9 months than 10 months).
This convention is news to me - though the confusion is not. Months are plain old calendar months in pregnancy (ie about 4.3 weeks).
https://www.verywellfamily.com/how-many-months-pregnant-am-i...
40 weeks is by convention from estimated last menstrual period, which is of course about 2 weeks prior to fertilization - so the actual gestastional period is closer to 38 weeks (that is closer to 9 months than 10 months).