Spontaneous labor and due date determination

This survey assumed that all due dates were set at 280 days, or 40 weeks, past last menstrual period (LMP). If LMP wasn't used, 280 was still the due date marker. For example if the baby came one day after its due date, I assumed that was day 281.

The graph & table on this page show how close the different methods of determination were. The closer they were to a 280 day average, the more accurate. So far no method seems to be dramatically more accurate than just counting 40 weeks past LMP.

Method of Due Date Determination	# of births	Average Arrival	Average Error (days)	Standard Deviation
LMP	5341	39W,5D	2	9.4
ovulation	1182	39W,6D	1	9.2
ultrasound	5005	39W,5D	2	9.8
Other	98	39W,5D	2	10.4

Due Date Survey Data Due date statistics: A study on the length of pregnancy Probability of delivery resulting from spontaneous labor after 35 weeks Probability of delivery within x days of a given date Length of pregnancy by week Spontaneous labor and due date determination Length of pregnancy, comparing subsequent births for individual moms Length of pregnancy for first time vs. second & third time moms Length of pregnancy, type of delivery Gestation vs. Birthweight Probablity of Induction after a given day Average day of spontaneous labor vs. age of mother at time of birth Are more babies born during a full moon? What's the most common day of the week for babies to be born? I'm still pregnant at 40W. What's it mean? Do winter babies arrive later? What if I know my conception date? Are boys or girls born later? Subsequent pregnancy date search How do inductions bias the due date statistics? Download the data Birth Stories Survey input dates

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