This graph shows only babies born as a result of spontaneous (non-induced) labor (76% of all participants).
Do babies come on their due dates? Not really. But they seem to come around their due dates. In the survey, only 666 out of 15028 (4.4%) spontaneously arrived on the exact day. But if you look around that date, the numbers get bigger fast... 3696 babies (24.6%) arrived spontaneously between 39 weeks 4 days and 40 weeks 3 days. 7031 (46.8%) arrived spontaneously within a week of their due date. Throwing out inductions makes those percentages even higher: 61.5% of all non-induced babies arrived within a week of their due date.
I also think this graph is important because it shows how meaningless it is to move a due date one or two days. For example I have a chart comparing first time moms to mothers who've had previous births, and it shows about a 1-2 day difference. But based on this graph, who cares about a day?
What I mean is this: a woman who's not induced has a 61.5% chance of giving birth within a week of her due date. Let's say we lie to her and tell her a date that's three days early. Now she has a 60.6% chance of delivering within a week of that "wrong" date. It's not really a huge difference.
|Day||In weeks||Babies Spontaneously Born|
Due Date Survey DataDue 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
Survey input dates
More ResourcesPregnancy Day-by-Day
Fast pregnancy calendar
Baby age calendar
EDD Icon Generator
Jo's Birth Story
Weeks vs. Months Explained
Charts generated by flot