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
13 1 24635W,1D26537W,6D
14 1 27339W,0D27238W,6D
14.5 4 26738W,1D27439W,1D
15 8 27138W,5D27539W,2D
15.5 10 27739W,4D27539W,2D
16 17 27639W,3D27539W,2D
16.5 17 27839W,5D27539W,2D
17 41 27539W,2D27539W,2D
17.5 35 27539W,2D27539W,2D
18 49 27238W,6D27539W,2D
18.5 63 27639W,3D27639W,3D
19 82 27739W,4D27639W,3D
19.5 75 27639W,3D27639W,3D
20 79 27739W,4D27639W,3D
20.5 113 27539W,2D27639W,3D
21 111 27639W,3D27639W,3D
21.5 112 27739W,4D27639W,3D
22 129 27639W,3D27639W,3D
22.5 129 27739W,4D27739W,4D
23 124 27539W,2D27739W,4D
23.5 125 27839W,5D27739W,4D
24 123 27939W,6D27739W,4D
24.5 141 27539W,2D27739W,4D
25 140 27639W,3D27739W,4D
25.5 138 27939W,6D27739W,4D
26 146 27739W,4D27739W,4D
26.5 156 27739W,4D27839W,5D
27 202 27839W,5D27839W,5D
27.5 201 27839W,5D27839W,5D
28 184 27939W,6D27839W,5D
28.5 201 27839W,5D27939W,6D
29 205 27939W,6D27939W,6D
29.5 194 27939W,6D27939W,6D
30 199 27939W,6D27939W,6D
30.5 189 27839W,5D27939W,6D
31 169 27839W,5D27939W,6D
31.5 153 28040W,0D27939W,6D
32 162 28040W,0D27939W,6D
32.5 158 27939W,6D27939W,6D
33 126 27939W,6D28040W,0D
33.5 110 27939W,6D27939W,6D
34 125 27939W,6D28040W,0D
34.5 90 28040W,0D28040W,0D
35 62 28040W,0D28040W,0D
35.5 67 28140W,1D28040W,0D
36 60 28140W,1D28040W,0D
36.5 43 28040W,0D28040W,0D
37 45 28240W,2D28040W,0D
37.5 43 27939W,6D28040W,0D
38 49 27939W,6D28040W,0D
38.5 33 28040W,0D28040W,0D
39 34 28240W,2D28040W,0D
39.5 28 28040W,0D28040W,0D
40 30 28040W,0D28040W,0D
40.5 18 28240W,2D28040W,0D
41 46 27839W,5D27939W,6D
41.5 40 27939W,6D27939W,6D
42 32 27939W,6D27939W,6D
42.5 10 28140W,1D27839W,5D
43 22 27839W,5D27839W,5D
43.5 8 27539W,2D27839W,5D
44 6 27439W,1D27939W,6D
44.5 10 28040W,0D27839W,5D
45 5 28540W,5D27839W,5D
45.5 3 28140W,1D28040W,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.

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Wed Nov 26 2:12 PM by spacefem in Random Weirdos


I fixed the chat pages, sorcery does have a web-based client that's working. next chat day is tuesday!

I forwarded the whole /chat to the wiki so we have one place to edit.

going public with the new pregnancy & parenting forum

Wed Nov 26 9:53 AM by spacefem in Pregnancy & Parenting

I started up this forum very recently - was going to give it some time to flesh out before I announced it to the world but what the heck, let's jump in the deep end.

I wanted to start our own pregnancy forum for several reasons:

- This site is frequented by smarter-than-average, geeky pregnant women looking up statistics, and I think you'd be nice to talk to more.

- I get the nicest emails from visitors and I think it's a shame that I'm the only one who gets to read your feedback.

- The world deserves a pregnancy forum that is not pink.

- The world deserves a pregnancy forum that is not smothered with ads for formula, stretch mark creams, and weight loss ads about "getting your body back"

- Several of us on are parents and might have some good advice to give. It's still kinda early to tell if I've screwed up my kids, but I'm optimistic.

how about it, pregnant lurkers? is this the kind of place where you could come in and say hi?

Christmas gifts for small children

Wed Nov 26 2:13 AM by spacefem in Pregnancy & Parenting

So I realize we should celebrate all that we have, but I was a bit surprised that someone in my babycenter month community plans to spend $2000, so far, on christmas presents for her 18-month-old: ... or_lo_poll

my child basically wants to go through the trash, she's happy with cardboard boxes, am I the only one who wants to keep Christmas a little downplayed at this age?

last year we wrapped up a hand-me-down baby toy that my oldest had forgotten about, just so the older kid would see her little sister get a gift. we spend $0. this year I may dramatically increase this by getting her some clothes.

bigger kids get more fun to buy for - but even then, it's weird for me to see four-year-olds getting their own ipads, right?

what's your shopping list look like this year? how do you keep it under control?

What's up?

Mon Nov 24 9:26 PM by DWH in Random Weirdos

Yooooooooooooooooo I keep forgetting to tell you I'm in LA until next Saturday and we should grab lunch if you're free!

Wait whaaaaaaaaaat, okay, I'm leaving town tomorrow for Thanksgiving but I'm going to move this discussion to Facebook.

And MFS, of course you should be scared. BAHAHAHAHA

books vs. movies the showdown!

Mon Nov 17 6:49 PM by Sonic# in Random Weirdos

Sometimes I try to see whether the film and the book each stand on their own. If they both do, I don't worry as much about which is better.

When I like the book more: usually it has to do with being so in love with the worldcraft and the descriptions of the book that the film can be entertaining and even moving but just doesn't have the form to develop those things I otherwise loved. See LOTR books (loooove) v. films (love). Sometimes the books are just better, usually because they're in the hands of an author much better than anything the film produced - see Fantastic Voyage by Isaac Asimov, or Dune compared even to David Lynch's version, or the ill-fated attempt to make an Earthsea miniseries.

When I like the film more: when there's something to the film that is brilliant and well-done in its own light. If I come away from the film really liking it, and think the book adds some things but isn't necessary, I like the film more. I'm thinking of Howl's Moving Castle as a good example, since I like the books but love even more its combination with Miyazaki's animation style and storytelling. This also goes for a lot of films that are novelized, like Star Wars. And sorry to the book The Princess Bride, but the film is the first to come to mind.

Which stereotypes do you completely shatter?

Wed Nov 26 10:02 AM by Sheppie in Random Weirdos

I am an American who is not stupid or ignorant. I have a broad knowledge of the world and I don't think we are the smartest. I can admit to a mistake, I have no problems with asking for directions when I need that, I can (and love to) cook and I love being around my girlfriend. I have never cheated, I believe in monogamy and I appreciate others being because of their characters and minds.

favorite movie about anyone having a baby

Wed Nov 26 4:41 AM by cwbyrvr in Pregnancy & Parenting

I voted for Juno just before I realized that Saved was an option. I like both, but I'd have to say I like Saved more.


Wed Nov 26 1:57 AM by Sonic# in Random Weirdos

First, humor me a bit. You see the word code-meshing. What do you think of?
I initially thought of some sort of script that recognizes multiple computer programing languages. So the term is new to me and has led me to more questions.

I have Appalacian English influences that come up in my speech at times without my notice. Then I have British English influence, but it only creeps into my spelling. With Appalacian English, I can seperate out what's "wrong" if asked, but I don't do so well categorizing my American spelling and British spelling. Does code-meshing need to be intentional?

Both questions are excellent. This first one I've been talking through a lot with my staff group. Our answer is that it doesn't have to be intentional, but by practicing it we might become more effective at code-meshing. In that way, it is a little like creative writing, where over time all of the genres and elements of writing you've been practicing come out in new and sometimes unanticipated ways. Of course we mix elements of different forms of speech, elements of genres, sayings and metaphors in our own idiolect (the way each individual speaks); practicing particular points of that mixture enriches what we can do there.


Fri Nov 21 6:37 AM by Storage and Disposal in Random Weirdos

I'm rarely in the mood to organize, but when I do it's really gratifying. The biggest thing is DVD's since I have like a thousand. Last time we organized it, we did so by color. I'm not sure what I'll do next.

The rest of the apartment could definitely use some organizing, but that's less fun.

stars by your name

Sat Nov 15 7:20 PM by rowan in Random Weirdos

*nibbles purple stars*

dealbreaker opinions

Wed Nov 26 10:00 AM by Dawn?Quixotic in Random Weirdos

I don't mind people being ignorant, until you point stuff out.
I flipped out on this guy when he said my theoretical description of a "berserker attacking people with his bare hands" (in the theoretical case it might be okay to pull your gun on someone who wasn't armed) that this described Michael Brown "to a tee".
Same deal with the case of the cosplayer who was murdered and supposedly was swinging the sword at people.
Probably didn't happen.
Do you seriously believe the media? The police? Would you believe anyone else accused of murder if they made up these excuses?
But forget eyewitnesses that say he wasn't doing anything.
We only want the witness that hate black people and will lie/misremember to suit their narrative.

calling obama a worthless moron

Sometimes these days I dunno how far off this is. I wasn't really amused by his response to Ferguson, but I suppose it was the "presidential" thing to say.

how can we spread the word on the touching thing?

Wed Nov 26 2:14 AM by spacefem in Pregnancy & Parenting

did anyone else have to deal with touchy people during their pregnancy? 'cause I did!

and I know they were well-meaning but it was WEIRD, and doubly weird when they'd ask "how's that baby!" and I... had no great response. good I guess? been a while since I called it on the phone?

why do people think it's okay to randomly feel you? and good snarky responses you found that made it stop? or did you just learn to deal?

Profile updates

Tue Nov 25 4:17 AM by cwbyrvr in Random Weirdos

My occupation used to be "college student/bum" which made it an interesting answer to what I wanted to be when I grew up for sure. Glad to see I wasn't the only one. I changed it, but I already forget what to... probably that I still don't know.

Are you prepared?

Thu Nov 20 12:25 PM by Aelwyn in Random Weirdos

No, not at all. I have nothing stocked in my place.
However I do live less than 2 minutes from a subway which doubles up as a bomb shelter. Handy.

when do you have to introvert?

Wed Nov 12 8:33 PM by melsbells in Random Weirdos

I've had a bit of the opposite reversal of Meperidine. I have always been extremely introverted, but for the past two years I have grown to crave social contact. My spouse is the most introverted person I have ever encountered and my primary social outlet. I think he'd like me to make friends just so I'll leave him alone sometimes. I'm in a class to learn the language now and sometimes I think I could be friends with one of the other foreigners. We can barely communicate with each other, but my current standards for friends-in-the-flesh are fairly low.