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
12 1 29041W,3D27739W,4D
12.5 1 28741W,0D27739W,4D
13 2 26437W,5D27439W,1D
13.5 1 28340W,3D27138W,5D
14 2 27739W,4D27339W,0D
14.5 4 26738W,1D27339W,0D
15 19 27038W,4D27439W,1D
15.5 26 27639W,3D27539W,2D
16 35 27439W,1D27639W,3D
16.5 40 27539W,2D27539W,2D
17 88 27639W,3D27639W,3D
17.5 76 27739W,4D27639W,3D
18 98 27439W,1D27639W,3D
18.5 125 27639W,3D27639W,3D
19 162 27639W,3D27639W,3D
19.5 166 27639W,3D27639W,3D
20 176 27639W,3D27639W,3D
20.5 203 27639W,3D27639W,3D
21 233 27739W,4D27639W,3D
21.5 216 27639W,3D27639W,3D
22 230 27639W,3D27739W,4D
22.5 239 27739W,4D27739W,4D
23 254 27639W,3D27739W,4D
23.5 240 27739W,4D27739W,4D
24 243 27939W,6D27739W,4D
24.5 307 27739W,4D27739W,4D
25 277 27739W,4D27839W,5D
25.5 276 27939W,6D27839W,5D
26 314 27739W,4D27839W,5D
26.5 342 27839W,5D27839W,5D
27 385 27839W,5D27839W,5D
27.5 374 27939W,6D27839W,5D
28 385 27939W,6D27939W,6D
28.5 412 27939W,6D27939W,6D
29 443 27939W,6D27939W,6D
29.5 422 27939W,6D27939W,6D
30 408 27939W,6D27939W,6D
30.5 424 27839W,5D27939W,6D
31 426 27939W,6D27939W,6D
31.5 369 28040W,0D27939W,6D
32 351 28040W,0D27939W,6D
32.5 351 28040W,0D28040W,0D
33 332 28040W,0D28040W,0D
33.5 272 28040W,0D28040W,0D
34 269 27939W,6D28040W,0D
34.5 204 27939W,6D28040W,0D
35 166 28040W,0D28040W,0D
35.5 155 28040W,0D28040W,0D
36 116 28040W,0D28040W,0D
36.5 104 28040W,0D28040W,0D
37 84 28140W,1D28040W,0D
37.5 70 27939W,6D28040W,0D
38 84 27839W,5D28040W,0D
38.5 71 28040W,0D27939W,6D
39 57 27939W,6D27939W,6D
39.5 45 28040W,0D27939W,6D
40 48 28040W,0D27939W,6D
40.5 36 28040W,0D27939W,6D
41 61 27939W,6D27939W,6D
41.5 54 27939W,6D27939W,6D
42 44 27939W,6D27939W,6D
42.5 31 27939W,6D27839W,5D
43 41 27839W,5D27939W,6D
43.5 26 27839W,5D27939W,6D
44 19 27739W,4D27839W,5D
44.5 23 28140W,1D27939W,6D
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

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