This baby’s due date is 9/24. Or is it 9/29? The 24th is the LMP date—Last Menstrual Period—and everyone accepts this date as truth, it would seem. But that date is entirely based on the mother’s recollection of when the first day of her last period was. The method seems problematic to me. The 29th is based upon an ultrasound taken early in the first trimester. That’s a pretty objective criterion, as long as the ultrasound operator’s hand is steady while drawing a circle around the fetus to measure its size. I trust it more.

But, since natural variation in what each woman’s body will consider “full term” is much greater than the difference between the two due dates…why should I trust either of them, except as an indication that it will happen, with high probability, somewhere within the four week span from late September to early October?

Nevertheless, anticipation will continue (justifiably) to build with passing days because the probability of birth today, given that the birth did not happen yesterday, is greater than the same conditional probability was yesterday.

At any rate, I’ve learned that the mother typically carries the baby for 38 weeks. The standard figure of 40 weeks is counting from the first day of the last menstrual period…and conception typically can’t happen for about two weeks after that.