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

[ Survey Results Intro | All Charts | Take the survey ]

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,3D27339W,0D
13 1 24635W,1D26938W,3D
13.5 1 28340W,3D27038W,4D
14 1 27339W,0D27238W,6D
14.5 3 26337W,4D27439W,1D
15 8 27138W,5D27639W,3D
15.5 10 27839W,5D27639W,3D
16 22 27639W,3D27539W,2D
16.5 18 27839W,5D27539W,2D
17 48 27639W,3D27539W,2D
17.5 38 27539W,2D27639W,3D
18 52 27339W,0D27639W,3D
18.5 68 27639W,3D27639W,3D
19 88 27739W,4D27639W,3D
19.5 91 27639W,3D27639W,3D
20 91 27739W,4D27639W,3D
20.5 129 27639W,3D27639W,3D
21 129 27639W,3D27639W,3D
21.5 129 27739W,4D27639W,3D
22 144 27639W,3D27739W,4D
22.5 143 27739W,4D27739W,4D
23 145 27639W,3D27739W,4D
23.5 138 27839W,5D27739W,4D
24 140 27939W,6D27739W,4D
24.5 159 27639W,3D27739W,4D
25 158 27639W,3D27739W,4D
25.5 155 27939W,6D27739W,4D
26 159 27739W,4D27739W,4D
26.5 178 27739W,4D27839W,5D
27 228 27839W,5D27839W,5D
27.5 223 27939W,6D27839W,5D
28 212 27939W,6D27839W,5D
28.5 220 27839W,5D27939W,6D
29 243 27939W,6D27939W,6D
29.5 221 27939W,6D27939W,6D
30 224 27939W,6D27939W,6D
30.5 217 27839W,5D27939W,6D
31 196 27839W,5D27939W,6D
31.5 173 28040W,0D27939W,6D
32 192 28040W,0D27939W,6D
32.5 177 27939W,6D27939W,6D
33 155 28040W,0D28040W,0D
33.5 128 28040W,0D28040W,0D
34 141 27939W,6D28040W,0D
34.5 101 27939W,6D28040W,0D
35 76 28040W,0D28040W,0D
35.5 74 28140W,1D28040W,0D
36 63 28140W,1D28040W,0D
36.5 53 27939W,6D28040W,0D
37 50 28240W,2D28040W,0D
37.5 45 27939W,6D28040W,0D
38 51 27939W,6D28040W,0D
38.5 36 28040W,0D28040W,0D
39 33 28240W,2D28040W,0D
39.5 33 27939W,6D28040W,0D
40 32 28140W,1D28040W,0D
40.5 19 28140W,1D27939W,6D
41 46 27839W,5D27939W,6D
41.5 44 27839W,5D27939W,6D
42 33 27839W,5D27839W,5D
42.5 14 28040W,0D27839W,5D
43 23 27839W,5D27839W,5D
43.5 13 27739W,4D27939W,6D
44 9 27639W,3D27939W,6D
44.5 10 28040W,0D27839W,5D
45 6 28640W,6D27939W,6D
45.5 4 27939W,6D28040W,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?
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
Charts generated by flot

Recent Comments

For more support, encouragement, Q&A,
you are invited to join our pregnancy forum. We are dedicated to answering complicated questions as logically as we possibly can.

if you need to breastfeed, please cover yourself

Fri May 29 3:43 PM by rowan in Pregnancy & Parenting

word to the wise though about summer babies - boob sunburn!!
Ok, THAT is a valid reason to cover up. Ouch!!!

getting along while doing things differently

Wed May 20 9:11 AM by Gnarlbanya in Pregnancy & Parenting

I'm finding it interesting that some people I've encountered (online) presume that if they know one of your pregnancy or parenting preferences or opinions, they can extrapolate them all. For example, in discussing pain relief options recently, after expressing my desire not to have an epidural it was also assumed that I would forego vaccinations for my child and would be automatically pro home VBAC. When I made it clear that this wasn't the case, people were more annoyed than they would have been had I just said I wanted an epidural. There seems to be a really odd sort of tribalism around many of these choices, and a strange playground mentality whereby you can't deviate from the 'norm' (made harder to navigate because different groups have very different norms). For me, my preference to go without an epidural is not out of any desire to have a more natural experience but more because I want to be able to walk around and I find the idea of having a catheter just horrible. That doesn't mean that I judge anyone else's choices or motives that differ from mine, though. I do think it's worth remembering that people may make identical choices for very different reasons.

the worst first birthday invite ever

Wed Apr 29 7:52 PM by melsbells in Pregnancy & Parenting

the understanding that when people buy gifts, it's their way of saying "hey, this says something about me, I want your kid to have it because we have a relationship." two ways.

Except sometimes those gifts are inappropriate. Part of me feels a lot of sympathy for these parents because what can I do with gifted clothing that is already too small for my kid except pass them on? What can I do with gifts that conflict with my personal beliefs, like a racist book that I don't want to inflict on anyone else either?

Tips and pitfalls for gender-neutral parenting

Mon Mar 30 9:25 PM by rowan in Pregnancy & Parenting

^I agree with that! :)

Part of "gender neutral" parenting is supplying the side of things that doesn't get given by other people.

How did you decide how many kids to have?

Fri Feb 27 2:42 AM by MFS in Pregnancy & Parenting

First 2 were on purpose, 3rd kinda not so much, 4th was totally an oops (when you think things are broken, they have this habit of fixing themselves). Made sure we were done after that. Aside from that, we knew we'd have at least 2, likely 3, but the timing was not at all what we thought we were "planning". Such is life.


Fri May 29 3:42 AM by ablotial in Pregnancy & Parenting

I'm fully prepared for all plans to go out the window - the ultimate goal will be sleeping (for everyone) so if we have to add the 'co', so be it.

Seconding this!

Can't find my tribe

Sat May 9 9:25 PM by Nedra in Pregnancy & Parenting

We've found relatively like-minded parents in the following ways:

-We went to undergrad at a liberal arts college and most of our alumni friends live in town still.
-I worked for 5 years at a charter school that was "girl-focused" (meaning, it was a girls school and any student who identified as a girl -- either biologically or socially -- could attend as long as they were cool with being part of a community of girls). Deconstructing sexism, heterosexism and racism was part of our mission and so the staff was very like-minded in this regard.

That's where virtually all my local, like-minded parents came from. Our church is pretty open-minded too. I don't know that I've ever seen a boy in a dress there, but I can't really imagine anyone batting an eye if we did. Certainly lots of boys playing with dolls and girls with trucks in the nursery.

When my own parents were in this position, they started a "non-sexist parenting group." Basically, they found ONE family who felt the same way, that family knew another, etc. They built a community intentionally by voicing out loud that that was what they wanted and spreading the word. They also found a lot of like-minded people through church. We are hippy-church and hippy-daycare/school people, so that helps.

Bilingual Babies

Mon Apr 13 11:41 AM by sakooon in Pregnancy & Parenting

Spacefem's husband no longer speaking Spanish and Nachos no longer speaking Dutch, I think are great examples of lacking motivation. Likewise, I had mentioned that my kid is unlikely to pick up Swedish, despite 10% of the population being native Swedish speakers, Swedish being one of the offical languages and therefore alongside Finnish everywhere, and having a Swedish speaking uncle.???

Interacting with parents whose choices you don't trust

Thu Mar 26 3:08 PM by rowan in Pregnancy & Parenting

How can you tell who has been vaccinated or not?
That's the tricky part, you can't really. So unless the parents say something you never actually know.


Fri Feb 6 4:35 AM by Zeph in Pregnancy & Parenting

Bonding with my future infant is a concern of mine, because my depression is debilitating. I'm relieved to know that normally functioning women don't feel that head-over-heels mushy baby love.

Flying during third trimester

Wed May 27 2:03 AM by ablotial in Pregnancy & Parenting

Thanks, I love the part about not being able to lower the tray table all the way :) I never would have thought of that.

Normally, my doctor said not to do aspirin or ibuprofen for pain relief, but only tylenol (acetemenophen) and even that only if -absolutely- needed after trying other remedies (like heat pack, cold pack, resting with lights closed eyes shut, etc). But the directions for flying specifically say to take one baby aspirin (81mg) a day for three days before the flight as well as the day of the flight to prevent blood clots. My guess is the risk of such a small dose is outweighed by the benefit of not getting blood clots for this particular situation.

The responsibility of choosing a name

Wed Apr 29 8:02 PM by melsbells in Pregnancy & Parenting

I fretted way too much about this.

Finland is one of the countries in the world with an approved name list. People can deviate from the list, but then they need to participate in bureacracy. Foreigners often get approval for names from their home culture, but as someone from the U.S., I'm not sure how straightforward it is to say "this cultural name appropriately represents my culture". Do I pick the cultures of my ancestors or modern U.S. conglomeration?

We went with approved names, but not the Swedish ones because my spouse felt weird giving a Swedish name without Swedish heritage. The Swedish names would have been most easily recognizable for my family.

Our main criteria ended up including:
I could pronounce it
we didn't hate the way Americans would pronounce it

We had to eliminate one contender because I sometimes mispronounced it, turning the name into a word that meant "failure".

Advice for non-parents?

Tue Apr 7 8:56 PM by Nedra in Pregnancy & Parenting

I definitely agree on the flexibility of where to meet. It makes a huge difference when you aren't stressed about your kid in a public place. Recently, I went to a tea shop with my daughter. Not only was the layout of the seating area very conducive to letting a toddler walk around a bit while still keeping a close eye on her, but there was plenty of room for my stroller and plenty of available tables. That is rare! It wasn't a huge space, but it was just laid out well for what we needed. I will definitely be suggesting it the next time a friend asks if we can get together. Let your parent friends choose the location! They know which places have changing tables and room to park a stroller.

How Good Parents Miss Child Sexual Abuse and 5 Questions to Change That

Tue Mar 24 3:20 AM by rowan in Pregnancy & Parenting

And that includes parents too - I try to always ask "can I have a hug/kiss" rather than "give me a hug/kiss" and that she can always always say no if she doesn't want to, even with me. (She's old enough now that I've had enough practice that even writing "give me a hug" sounds weird to me)

Also I think on a more general level it's good to practice asking these kinds of questions anyway. Not just for abuse, but in general if you want to know what's going on in their life. Asking "how was school" gets an "I dunno" even now, but asking more specific things like "What was something funny that happened today" or "What did you do at recess?" really gets her talking more. Not sure where I read that, but the kinds of questions above made me think that sometimes just asking a better question will help get at what you want to know more than asking generalities.

The other thing is definitely definitely not making judgment on those things that they're saying. Instead try "What did you think about that ?" or "What did you do when happened?" "What would make you feel safe?" "What could you try if that happens again?" "Is there anything you'd like me to do?" These are things that I've asked wrt other kids on the playground (pushing etc) but I think it's the same idea in terms of empowering the child to talk about things that happen and letting them help come to the conclusions. Which isn't to say you can't help them get there by suggesting actions they could do, etc, just that if you get them talking about things that happen on a daily basis then if something weird happens then they'll likely be more comfortable telling you, especially if you've already shown them what boundaries there are and respecting those boundaries (like not tickling if they say they don't want to be tickled etc).

34 Weeks

Fri Jan 23 11:57 PM by Sonic# in Pregnancy & Parenting

Probably not. As we pointed out in the other topic, 34 weeks isn't even on the chart because it's so rare:

You'd be better off worrying over a car accident.