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 94 27439W,1D27639W,3D
18.5 119 27639W,3D27639W,3D
19 158 27639W,3D27639W,3D
19.5 162 27639W,3D27639W,3D
20 172 27639W,3D27639W,3D
20.5 201 27639W,3D27639W,3D
21 230 27739W,4D27639W,3D
21.5 209 27639W,3D27639W,3D
22 222 27639W,3D27639W,3D
22.5 231 27639W,3D27739W,4D
23 247 27639W,3D27739W,4D
23.5 235 27739W,4D27739W,4D
24 233 27939W,6D27739W,4D
24.5 295 27739W,4D27739W,4D
25 268 27739W,4D27839W,5D
25.5 271 27939W,6D27839W,5D
26 305 27739W,4D27839W,5D
26.5 335 27839W,5D27839W,5D
27 371 27839W,5D27839W,5D
27.5 367 27939W,6D27839W,5D
28 373 27939W,6D27939W,6D
28.5 400 27939W,6D27939W,6D
29 429 27939W,6D27939W,6D
29.5 416 27939W,6D27939W,6D
30 393 27939W,6D27939W,6D
30.5 409 27839W,5D27939W,6D
31 416 27939W,6D27939W,6D
31.5 358 28040W,0D27939W,6D
32 340 28040W,0D27939W,6D
32.5 346 28040W,0D28040W,0D
33 326 28040W,0D28040W,0D
33.5 265 28040W,0D28040W,0D
34 261 27939W,6D28040W,0D
34.5 201 27939W,6D28040W,0D
35 163 28040W,0D28040W,0D
35.5 148 28040W,0D28040W,0D
36 111 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 71 28040W,0D27939W,6D
39 53 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 50 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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