Length of pregnancy by week

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This graph groups the births by weeks. For instance, "week 40" means days 280-286.


Excluding inductions, here are the percentages for each week: These percentages are based on the 5666 babies born spontaneously, excluding the 1853 babies who were induced. As with the graph, "at 40 weeks" means babies born on 40 weeks, 0 days through 40 weeks, 6 days.

Data Table

Total births: 7519
WeekAll births% of totalRunning total %Spontaneous% of totalRunning total %
351041.41.4 821.11.1
362132.84.2 1742.33.4
374956.610.8 37658.4
38101213.524.3 79410.619
39188425.149.4 147319.638.6
40219229.278.6 174923.361.9
41135818.196.7 89611.973.8
422503.3100 1151.575.3
43110.1100.1 70.175.4
The "running total %" basically tells you how many babies have been born by the end of the week. For example, 38.6% of women went into labor spontaneously before they hit week 40.

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.

favorite movie about anyone having a baby

Thu Nov 27 12:38 AM by Meperidine in Pregnancy & Parenting

^ ha!

I had to say Saved!, because I saw it before I had observed and become sick of the "teenager gets pregnant but is eventually happy about it" narrative. (I did a book for work this month about a virgin teenager who gets pregnant through immaculate conception; it's the only book I read for them that made me think "this book should not exist.")

I didn't care for Juno, which came out when I was about 16. It might just have been my perspective at the time, but it all seemed too precious and too much like an adult's obnoxious idea of what teenagers are like.

dealbreaker opinions

Wed Nov 26 5:29 PM by Storage and Disposal in Random Weirdos

really you guys? I unfriend all the time!

why mute someone? that means they're still going to be seeing your posts, commenting on your photos, getting to be "in" your life, and never know anything changed. what good is happening by keeping them around?

My former art teacher is quite conservative, but I still like his comments on my artwork.

I put people I think are otherwise perfectly delightful on mute because they flood facebook with useless crap. I don't want them to get the idea that I hate them, but I don't feel like seeing pages of what they have to say.

I think a lot of people have opinions I don't care for. Rather than offending someone I know and respect in person, I choose to just not see it. Facebook has a knack for showing sides of people I don't want to see, but it's just small sides of them. To me, it's not worth shutting out the person completely. After awhile, I occasionally take them off mute to see if they stopped with their nonsense.

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?

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.

Christmas gifts for small children

Wed Nov 26 10:06 PM by Sonic# in Pregnancy & Parenting

When I was little I remember getting a few toys. My parents didn't have that much money (I learned later), but even getting a few things (some clothes, a bucket of duplos) was plenty. The family gifts were the big ones - things like a computer (OMG a Commodore 128) and two very nice sleds.

Which stereotypes do you completely shatter?

Wed Nov 26 3:46 PM by C-3PO in Random Weirdos

I'm male, but I'm 5'6", I don't like sports, I'm asexual, I have a lousy sense of direction, and I struggle with Mathematics.

I'm from Texas, but I take public transportation, speak English correctly, tend towards agnosticism, and dislike competitive attitudes.

I'm white, but my family isn't wealthy or educated. (I actually kind of wish I fit this one.)


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*

how can we spread the word on the touching thing?

Wed Nov 26 8:02 PM by melsbells in Pregnancy & Parenting

I almost never had to deal with this. I was living in a remote area and not interacting much with others. Also, the culture here doesn't seem conducive of interacting with people by touching them.

One of my spouse's young nieces touched my belly and I didn't know how to tell her not to do it. She was immediately corrected by her mother about not touching people without permission.

Then my parents arrived. I mostly just dealt with their touch, but probably not with much class.

forum suggestion box

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.

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.