The lunar month and gestation

[mgansten at sbbs.se]

Luis Gonzalez-Reimann writes:

>>The progress through the various embryonic stages is
>>denoted by weeks, and the total gestational period is, if memory serves (I
>>don't have the text at hand) 38 weeks.
>
>The average duration of pregnancy is about 280 days, or 40 weeks of 7 days.

Well, no, not if you mean the actual period of gestation; the average would
actually be about 38 weeks, as reckoned from the time of conception (though
there is plenty of scope for individual variation). The 40 week average
refers to the time of pregnancy as reckoned from the first day of the
mother's last period, which is more easily discernible; conception is
supposed to take place two weeks thereafter.

Martin Gansten