Average day of spontaneous labor vs. age of mother at time of birth

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I read somewhere that maternal age has something to do with when labor sets in, so I included it in the survey. I found nothing terribly interesting or conclusive.

This sort of validated my decision to keep the survey simple and not consider every little thing in the world that people are curious about. Could the average day change depending on your age, ethnicity, whether you were on the pill, country of origin, etc? Maybe. But we're talking about something where with a standard deviation of over a week here... about the same number of people give birth on day 279 as on day 287. So if some random thing changes the average by 2 days will that knowledge help make your due date any more accurate? I'm thinking no.


Data table - Average lenth of pregnancy per age

Age# of participantsAverage day of spontaneous laborAverage day including ± 1 year of age
16 20 27439W,1D27639W,3D
16.5 40 27539W,2D27639W,3D
17 88 27639W,3D27639W,3D
17.5 73 27739W,4D27639W,3D
18 100 27439W,1D27639W,3D
18.5 121 27639W,3D27639W,3D
19 164 27639W,3D27639W,3D
19.5 166 27639W,3D27639W,3D
20 177 27639W,3D27639W,3D
20.5 204 27639W,3D27639W,3D
21 233 27739W,4D27639W,3D
21.5 213 27639W,3D27639W,3D
22 224 27639W,3D27639W,3D
22.5 235 27739W,4D27739W,4D
23 250 27639W,3D27739W,4D
23.5 238 27739W,4D27739W,4D
24 242 27939W,6D27739W,4D
24.5 302 27739W,4D27739W,4D
25 274 27739W,4D27839W,5D
25.5 277 27939W,6D27839W,5D
26 309 27739W,4D27839W,5D
26.5 341 27839W,5D27839W,5D
27 380 27839W,5D27839W,5D
27.5 369 27939W,6D27839W,5D
28 384 27939W,6D27939W,6D
28.5 404 27939W,6D27939W,6D
29 439 27939W,6D27939W,6D
29.5 420 27939W,6D27939W,6D
30 408 27939W,6D27939W,6D
30.5 425 27839W,5D27939W,6D
31 422 27939W,6D27939W,6D
31.5 365 28040W,0D27939W,6D
32 350 27939W,6D27939W,6D
32.5 360 28040W,0D28040W,0D
33 333 27939W,6D28040W,0D
33.5 271 28040W,0D28040W,0D
34 271 27939W,6D28040W,0D
34.5 202 27939W,6D28040W,0D
35 168 28040W,0D28040W,0D
35.5 157 28040W,0D28040W,0D
36 113 28040W,0D28040W,0D
36.5 107 28040W,0D28040W,0D
37 85 28140W,1D28040W,0D
37.5 69 27939W,6D28040W,0D
38 83 27839W,5D28040W,0D
38.5 71 28040W,0D27939W,6D
39 53 27939W,6D27939W,6D
39.5 46 28040W,0D27939W,6D
40 45 28040W,0D27939W,6D
40.5 32 28040W,0D27939W,6D
41 60 27939W,6D27939W,6D
41.5 51 27839W,5D27939W,6D
42 44 27939W,6D27939W,6D
42.5 30 27939W,6D27839W,5D
43 39 27839W,5D27839W,5D
43.5 25 27839W,5D27939W,6D
44 17 27739W,4D27839W,5D
44.5 22 28240W,2D27839W,5D
45 15 28040W,0D27939W,6D
45.5 19 27639W,3D27939W,6D
46 4 28440W,4D28040W,0D

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

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Fast pregnancy calendar
Baby age calendar
EDD Icon Generator
Jo's Birth Story
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