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,5D27339W,0D
13.5 1 28340W,3D27038W,4D
14 2 27739W,4D27238W,6D
14.5 3 26337W,4D27339W,0D
15 17 26838W,2D27439W,1D
15.5 21 27639W,3D27539W,2D
16 35 27439W,1D27539W,2D
16.5 39 27539W,2D27539W,2D
17 87 27639W,3D27639W,3D
17.5 73 27739W,4D27639W,3D
18 93 27439W,1D27639W,3D
18.5 120 27639W,3D27639W,3D
19 157 27639W,3D27639W,3D
19.5 161 27639W,3D27639W,3D
20 170 27639W,3D27639W,3D
20.5 201 27639W,3D27639W,3D
21 230 27739W,4D27639W,3D
21.5 205 27639W,3D27639W,3D
22 221 27639W,3D27639W,3D
22.5 231 27639W,3D27739W,4D
23 247 27639W,3D27739W,4D
23.5 234 27739W,4D27739W,4D
24 232 27939W,6D27739W,4D
24.5 293 27739W,4D27739W,4D
25 268 27739W,4D27839W,5D
25.5 268 27939W,6D27839W,5D
26 305 27739W,4D27839W,5D
26.5 331 27839W,5D27839W,5D
27 367 27839W,5D27839W,5D
27.5 365 27939W,6D27839W,5D
28 372 27939W,6D27939W,6D
28.5 400 27939W,6D27939W,6D
29 426 27939W,6D27939W,6D
29.5 413 27939W,6D27939W,6D
30 391 27939W,6D27939W,6D
30.5 409 27839W,5D27939W,6D
31 411 27939W,6D27939W,6D
31.5 356 28040W,0D27939W,6D
32 339 28040W,0D27939W,6D
32.5 346 28040W,0D28040W,0D
33 324 28040W,0D28040W,0D
33.5 263 28040W,0D28040W,0D
34 259 27939W,6D28040W,0D
34.5 201 27939W,6D28040W,0D
35 162 28040W,0D28040W,0D
35.5 147 28040W,0D28040W,0D
36 109 28040W,0D28040W,0D
36.5 104 28040W,0D28040W,0D
37 84 28140W,1D28040W,0D
37.5 68 27939W,6D28040W,0D
38 83 27839W,5D28040W,0D
38.5 70 28040W,0D27939W,6D
39 52 27939W,6D27939W,6D
39.5 44 28040W,0D27939W,6D
40 45 28040W,0D27939W,6D
40.5 32 28040W,0D27939W,6D
41 60 27939W,6D27939W,6D
41.5 52 27839W,5D27939W,6D
42 44 27939W,6D27939W,6D
42.5 30 27939W,6D27839W,5D
43 39 27839W,5D27939W,6D
43.5 25 27839W,5D27939W,6D
44 17 27739W,4D27839W,5D
44.5 23 28140W,1D27839W,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

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