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,0D27639W,3D
13 1 24635W,1D27138W,5D
13.5 1 28340W,3D27138W,5D
14 1 27339W,0D27339W,0D
14.5 3 26337W,4D27439W,1D
15 8 27138W,5D27539W,2D
15.5 11 27739W,4D27539W,2D
16 22 27639W,3D27539W,2D
16.5 21 27839W,5D27539W,2D
17 54 27639W,3D27539W,2D
17.5 41 27539W,2D27639W,3D
18 56 27339W,0D27639W,3D
18.5 69 27639W,3D27639W,3D
19 94 27739W,4D27639W,3D
19.5 96 27639W,3D27639W,3D
20 99 27639W,3D27639W,3D
20.5 135 27639W,3D27639W,3D
21 136 27739W,4D27639W,3D
21.5 136 27739W,4D27639W,3D
22 152 27739W,4D27739W,4D
22.5 153 27739W,4D27739W,4D
23 156 27539W,2D27739W,4D
23.5 154 27739W,4D27739W,4D
24 149 27939W,6D27739W,4D
24.5 174 27639W,3D27739W,4D
25 170 27639W,3D27739W,4D
25.5 163 27939W,6D27739W,4D
26 170 27739W,4D27739W,4D
26.5 188 27739W,4D27839W,5D
27 236 27839W,5D27839W,5D
27.5 233 27939W,6D27839W,5D
28 220 27939W,6D27839W,5D
28.5 240 27839W,5D27939W,6D
29 258 27939W,6D27939W,6D
29.5 239 27939W,6D27939W,6D
30 233 27939W,6D27939W,6D
30.5 231 27839W,5D27939W,6D
31 214 27839W,5D27939W,6D
31.5 184 28040W,0D27939W,6D
32 205 28040W,0D27939W,6D
32.5 187 27939W,6D27939W,6D
33 165 28040W,0D28040W,0D
33.5 139 28040W,0D28040W,0D
34 151 27939W,6D28040W,0D
34.5 113 27939W,6D28040W,0D
35 84 28040W,0D28040W,0D
35.5 75 28140W,1D28040W,0D
36 68 28140W,1D28040W,0D
36.5 61 27939W,6D28040W,0D
37 55 28140W,1D28040W,0D
37.5 46 28040W,0D28040W,0D
38 53 27939W,6D28040W,0D
38.5 38 28040W,0D28040W,0D
39 34 28240W,2D28040W,0D
39.5 33 27939W,6D28040W,0D
40 33 28140W,1D28040W,0D
40.5 19 28140W,1D27939W,6D
41 47 27839W,5D27939W,6D
41.5 45 27839W,5D27939W,6D
42 33 27839W,5D27839W,5D
42.5 16 28040W,0D27839W,5D
43 23 27839W,5D27839W,5D
43.5 16 27639W,3D27839W,5D
44 10 27639W,3D27839W,5D
44.5 10 28040W,0D27839W,5D
45 8 28340W,3D27839W,5D
45.5 8 27839W,5D27939W,6D

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?
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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Recent Comments

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Braxton Hicks questions

Fri Aug 28 5:10 PM by geerlady in Pregnancy & Parenting

Was just in the hospital for a pre-term labour false alarm earlier this week.

My Braxton Hicks have changed this time around to be sometimes painful, period-like cramps extending to my lower back with contractions that are fairly regular (every 10 to 15 minutes regardless of what I am doing). But they have been medically confirmed to still just be Braxton Hicks :o

As a general comment, my BH have always been symmetric, so symmetry was never a good marker for me.

So... second time around and I still can't tell the difference :)

What new thing did your baby do this week?

Mon Aug 24 5:56 PM by Nachos in Pregnancy & Parenting

It's not my baby, but my sister taught my best friend's baby how to fist bump and I taught her how to say yolo. Heh.

What the Hell just entered my earhole?

Mon Aug 17 11:34 AM by DarkOne in Pregnancy & Parenting

Oh that reminded me of a friend's kid... My friend, her 6-yr old son and her 9-yr old daughter were driving to school in the morning, when the son proudly declared "When I grow up I want to be a racist." My friend said she went O_O and her daughter went on a rant as to how horrible of an idea that was... The son was all sad and confused when he responded "But I really love race cars!"

That cracked me up.

Kids books we hate

Mon Aug 3 1:10 PM by Sonic# in Pregnancy & Parenting

I absolutely loved at least one of the Berenstain Bears books (one based off of the Tortoise and the Hare), but I also hate at least one of them. The Berenstain Bears and the Trouble With Chores features a Mama Bear exasperated that no one is doing chores, with the kid bears and Papa Bear keep excusing themselves out of doing them. Rather than coming to some equitable distribution of labor by the end, the house gets really bad and the kids and pop finally binge clean. The situation didn't seem solved; Mama Bear just seemed pacified.

for all you moms and future moms

Tue Jul 21 2:28 AM by DarkOne in Pregnancy & Parenting

Eek and here I was about to say this felt like a tame version of Mother Lover.

Body Betrayal

Thu Aug 27 8:44 PM by mathnome in Pregnancy & Parenting


I'm currently 37 weeks, and while almost all my immediate coworkers have been super supportive of my being at work (and planning to continue being at work), I got a "tsk tsk" from another woman the other day about not taking my leave yet, and she hasn't been the first one. (Interestingly, so far it's only been the women who seem to think I'm supposed to leave already.)

Anyway, my line has been, "I'm really enjoying my project right now. I might as well enjoy it while I can!" (Which is true, and also generally shuts them up.)

Good luck! I hope the BP stays under the magic threshold.

What did you hate hearing when you were pregnant?

Mon Aug 24 11:52 AM by DarkOne in Pregnancy & Parenting

3. I think you're putting on too much weight. You know it''s going to make it harder to get your body back. (I'm 6 months post baby today, so now the comments have turned to "I told you!")


let's list our favorite children's books

Tue Aug 11 3:49 AM by DarkOne in Pregnancy & Parenting

As a grade school kid, I spent a lot of time perusing dictionaries, atlases and world almanacs. I blame it on my Big Bird's Sesame Street Dictionary, which was awesome:


Did anyone else own these? I have the full set stashed somewhere for when my kid is old enough.

RIE parenting

Sat Aug 1 2:09 AM by ohbonobogirl in Pregnancy & Parenting

I encountered this randomly the other day. Now I need to go dig some more into it...

the wonder weeks: practical help for parents or self-fulfilling quackery?

Mon Jul 20 2:29 AM by geerlady in Pregnancy & Parenting

I am actually a big fan of the wonder weeks. I found it better than most popular level books looking at infant development. My son was right on the clock for the fussy/happy times, and it was interesting to look for the new skills that I might not have noticed if I hadn't been watching for them.

On the other hand, I stumbled upon this accidentally, so didn't have any hype surrounding it. I also read the author biographies before picking up the book, so took everything with a grain of salt knowing that 1) the authors specialized in chimpanzees, not humans, and developed their theories based on chimps; 2) the bulk of the research is greater than 20 years old and so much of the book is out-dated; and 3) given #'s 1&2, incidental parenting advice had to be filtered.

That said, I still found the book useful and regularly recommend it to people.

Happy Birthday, Baby Bird!

Thu Aug 27 12:57 PM by ablotial in Pregnancy & Parenting

Cute kids, and I love the cupcake theme!

mom guilt bingo

Sun Aug 23 11:06 AM by ohbonobogirl in Pregnancy & Parenting

Adding to the newborn edition:
Knowingly fell asleep on the couch with baby on your chest because...sleep...
Used a tablet or phone to surf net or play games while nursing rather than cherishing every moment
Took baby out in public solely because it's really great to hear strangers compliment your adorable little being.

teething necklaces

Tue Aug 4 7:12 PM by DarkOne in Pregnancy & Parenting

They'll chew on anything and everything. And I think you may have the scale wrong. These are large silicone beads. Think of it as a teething/chewing toy that is long enough to be worn around mom's neck. This isn't a string of pearls that will break if you tug on it and you'll and up with a mess of pearls on the floor or in baby's mouth. Google images for "babies and chew beads".
And these are not at all related to those dumb amber necklaces...

do you have a parenting goal?

Sun Jul 26 5:16 PM by rosefox in Pregnancy & Parenting

I'm definitely in the "happy healthy child is my only goal" camp. I know some people who are superstars in their chosen fields. From what I can tell, being a superstar is completely exhausting and often really psychologically taxing. So if my kid isn't naturally inclined that way, I certainly don't intend to push them.

If I'm hoping for anything, I hope they'll end up being a quirky artsy/techy type like just about everyone else in the family. But my brother's a corporate lawyer and I love him anyway, so even if our kid turns out to be a white sheep, they'll just bond with Uncle A and it'll all be fine. :)

Spacefem's homemade playdoh recipe

Mon Jul 13 3:01 AM by Zeph in Pregnancy & Parenting

A parent in my Kindergarten class would bring us homemade purple play dough that smelled like grape!