Length of pregnancy for first time vs. second & third time moms

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Cumulative Distribution

This graph shows the percentage of births that'd occured on or before a given day, like a running total.

There's a popular rumor out there that first time moms are very likely to go past their due dates... sometimes even way past. I had people tell me to expect to go a week overdue. Here's what I found in the survey. Considering only births resulting from spontaneous labor:

So why the rumor about first time moms going late? There are articles all over the web that say the average first time mother goes eight days overdue and doesn't have her baby until 41 weeks, 1 day. I say hold off, people. There's only one study that suggested this median: The length of uncomplicated human gestation (Mittendorf et al). The study was simply a record of a few hundred women at one private practice. Only 31 of those women were first time mothers. The study itself calls for further research. You can read it here. Given the small sample size and drastic deviation from the large-scale studies cited in my introduction, I'd suggest we dispell the rumor a bit and calm everybody down. And teach bloggers to read medical studies. Due date statistics are much better looked at as an epidemiology topic than a medical one, anyway.

Average length of pregnancy, by number of subsequent previous births

# of previous births# of birthsAverage Arrival

Daily probabilities of spontaneous labor, by number of subsequent previous births

Day 0 previous births 1 previous birth 2 or more previous births
#% #% #%
245 8 0.2 3 0.2 1 1.1
246 12 0.3 0 0 3 3.3
247 3 0.1 3 0.2 1 1.1
248 13 0.3 3 0.2 1 1.1
249 10 0.2 3 0.2 1 1.1
250 14 0.3 1 0.1 1 1.1
251 9 0.2 3 0.2 1 1.1
252 18 0.4 6 0.5 0 0
253 17 0.4 2 0.2 0 0
254 14 0.3 9 0.7 1 1.1
255 27 0.6 4 0.3 1 1.1
256 14 0.3 7 0.5 1 1.1
257 14 0.3 11 0.8 1 1.1
258 23 0.5 2 0.2 2 2.2
259 31 0.7 12 0.9 1 1.1
260 33 0.7 6 0.5 1 1.1
261 29 0.6 7 0.5 4 4.4
262 56 1.2 8 0.6 3 3.3
263 52 1.1 16 1.2 2 2.2
264 40 0.9 16 1.2 2 2.2
265 62 1.3 19 1.5 2 2.2
266 65 1.4 23 1.8 2 2.2
267 68 1.5 17 1.3 1 1.1
268 59 1.3 18 1.4 2 2.2
269 93 2 27 2.1 5 5.5
270 117 2.5 31 2.4 1 1.1
271 99 2.1 31 2.4 1 1.1
272 118 2.5 46 3.5 1 1.1
273 143 3.1 41 3.2 2 2.2
274 135 2.9 29 2.2 1 1.1
275 141 3 41 3.2 4 4.4
276 167 3.6 59 4.5 4 4.4
277 184 4 58 4.5 1 1.1
278 196 4.2 52 4 1 1.1
279 234 5 56 4.3 1 1.1
280 233 5 64 4.9 1 1.1
281 249 5.4 53 4.1 1 1.1
282 196 4.2 72 5.5 1 1.1
283 211 4.6 50 3.8 4 4.4
284 198 4.3 42 3.2 2 2.2
285 197 4.3 50 3.8 1 1.1
286 186 4 66 5.1 3 3.3
287 191 4.1 57 4.4 1 1.1
288 136 2.9 31 2.4 1 1.1
289 110 2.4 34 2.6 1 1.1
290 105 2.3 39 3 1 1.1
291 98 2.1 12 0.9 1 1.1
292 55 1.2 25 1.9 2 2.2
293 55 1.2 8 0.6 1 1.1
294 41 0.9 11 0.8 7 7.7
295 11 0.2 7 0.5 1 1.1
296 15 0.3 5 0.4 2 2.2
297 9 0.2 1 0.1 1 1.1
298 5 0.1 3 0.2 1 1.1
299 5 0.1 0 0 1 1.1
300 2 0 0 0 0 0

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.


Wed May 27 10:34 AM by Gnarlbanya 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.

Now I'm expecting my second baby (31 weeks along).
31 weeks here, too!

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.

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.

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.

I would Just like some femnist thought on this

Tue May 26 12:30 AM by Wolf in Pregnancy & Parenting

Hello just to start and get this out of the way. I am a Male, and I don't agree with.....well just about anything with modern feminism today, mostly because of what I have seen, and a lot of the article I read. However I am here to try and hopefully find out that these stories I here and articles I read are not true feminist, and that actual feminist are capable of seeing logic, and not intentionally misrepresent anything that disagrees with them. So I was hoping a few of you could answer some question I have, about some things I have come across.

The first thing I would like you thoughts on are this articles I found from a few year back by Melanie McDonagh Titled Paternity Tests Rob Women Of Their Hold Over Men here's the source, I believe it may be behind a pay wall though. ... 183263.ece

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.