How do they determine the date of delivery?

Question

I happened to be observed by two OBs in two different countries. Though I gave the same info to both like the date of my last period, they determined different delivery dates (1 week difference). I just wonder how do they figure out and if the system is different in different countries?

Answer 1

No, it isn't different in different countries; one of them made a mistake. If you know the exact date of ovulation, you add 38 weeks. Otherwise, the *estimated* due date is the first day of your last period (LMP) plus 40 weeks.

You can figure out which is correct yourself by counting, or by using this shortcut. 9 calendar months is almost exactly 39 weeks. Go forward 9 months from either the date of ovulation or LMP, then go back one week (if you used ovulation) or forward one week (for LMP). Move to the nearest date that is the same day of the week as ovulation/LMP to make it precisely 38/40 weeks.

Answer 2

I always counted back 3 months from the day my last cycle started then ad 7 days, and I've been real close. Of course they say give or take 2 weeks.

Answer 3

Other factors in your pregnancy might make the due date different. And, some docs like to add one week to the date if it's the first baby.

The reality is that we never really know when babe will arrive, from very early to weeks late.

Answer 4

count back 3 months and add a week from the first day of your last period..

Answer 5

Still 95% is wrong in guessing the date. That's why you can get this fabulous offer of bithdaycards if you guess the date correctly.