Length of pregnancy by week

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This graph groups the births by weeks. For instance, "week 40" means days 280-286.


Excluding inductions, here are the percentages for each week: These percentages are based on the 11949 babies born spontaneously, excluding the 3767 babies who were induced. As with the graph, "at 40 weeks" means babies born on 40 weeks, 0 days through 40 weeks, 6 days.

Data Table

Total births: 15716
WeekAll births% of totalRunning total %Spontaneous% of totalRunning total %
352171.41.4 1691.11.1
364172.74.1 3252.13.2
379886.310.4 7664.98.1
38206213.123.5 164010.418.5
39382524.347.8 302619.337.8
40468429.877.6 379824.262
4129911996.6 197312.674.6
425113.399.9 2391.576.1
43210.1100 130.176.2
The "running total %" basically tells you how many babies have been born by the end of the week. For example, 37.8% of women went into labor spontaneously before they hit week 40.

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

More Resources

Pregnancy Day-by-Day
Fast pregnancy calendar
Baby age calendar
EDD Icon Generator
Jo's Birth Story
Weeks vs. Months Explained
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