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
246 12 0.3 0 0 3 3.1
247 3 0.1 3 0.2 1 1
248 13 0.3 3 0.2 1 1
249 11 0.2 3 0.2 1 1
250 14 0.3 2 0.2 1 1
251 9 0.2 3 0.2 2 2.1
252 19 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
255 27 0.6 4 0.3 1 1
256 15 0.3 9 0.7 1 1
257 14 0.3 11 0.8 1 1
258 23 0.5 3 0.2 2 2.1
259 32 0.7 12 0.9 2 2.1
260 35 0.7 6 0.5 1 1
261 30 0.6 7 0.5 4 4.2
262 57 1.2 8 0.6 3 3.1
263 53 1.1 17 1.3 3 3.1
264 41 0.9 16 1.2 2 2.1
265 64 1.4 19 1.4 2 2.1
266 67 1.4 23 1.7 2 2.1
267 71 1.5 17 1.3 1 1
268 62 1.3 18 1.4 2 2.1
269 97 2 28 2.1 5 5.2
270 117 2.5 31 2.3 1 1
271 100 2.1 31 2.3 1 1
272 121 2.6 46 3.5 1 1
273 145 3.1 42 3.2 2 2.1
274 137 2.9 30 2.3 1 1
275 145 3.1 43 3.3 4 4.2
276 168 3.5 60 4.5 4 4.2
277 190 4 58 4.4 1 1
278 199 4.2 52 3.9 1 1
279 236 5 57 4.3 1 1
280 243 5.1 66 5 1 1
281 257 5.4 54 4.1 1 1
282 200 4.2 72 5.5 1 1
283 219 4.6 50 3.8 5 5.2
284 203 4.3 43 3.3 2 2.1
285 200 4.2 51 3.9 1 1
286 189 4 66 5 4 4.2
287 194 4.1 57 4.3 1 1
288 139 2.9 32 2.4 1 1
289 111 2.3 34 2.6 1 1
290 107 2.3 40 3 1 1
291 100 2.1 12 0.9 1 1
292 56 1.2 25 1.9 2 2.1
293 55 1.2 9 0.7 1 1
294 41 0.9 11 0.8 7 7.3
295 11 0.2 7 0.5 1 1
296 15 0.3 5 0.4 2 2.1
297 9 0.2 1 0.1 1 1
298 5 0.1 3 0.2 1 1
299 5 0.1 0 0 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

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you are invited to join our pregnancy forum. We are dedicated to answering complicated questions as logically as we possibly can.

Antidepressants during pregnancy

Fri Jul 3 10:33 AM by Luis87 in Pregnancy & Parenting

Hey, you should never take antidepressants during pregnancy. Instead of that you can do some yoga and other exercises. The acupunctures also help in that. My sister works at a domestic streetsville acupuncture center and she tells all these things to us.

Pregnancy insomnia

Thu Jun 25 9:05 AM by Gnarlbanya in Pregnancy & Parenting

Thanks for the tips. It's not so much getting to sleep that's the problem, it's staying that way that is causing the issue - too many things waking me up. I seem to be in a bit of a pattern now of alternating good and bad nights, which I guess I can live with. Meanwhile, Netflix is getting a damn good workout in the early hours.

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 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.

if you need to breastfeed, please cover yourself

Thu Jun 25 11:40 AM by spacefem in Pregnancy & Parenting

I'm late on this conversation, but yes staring would probably make me feel weird. BUT I've noticed that if you strike up a quick conversation it's less weird, and most women really appreciate it because let's face it nursing can get to be boring as hell.

so I was at this party and a woman was nursing her son and all the chairs were taken except the one right next to her. I wanted to sit down, and I also will confess that the site of a baby getting milk drunk is the best thing to witness, it'll make your day, so I plopped down, but I asked her first too. It was a "Hey, can I sit here? Thanks. I'm spacefem. Looks like somebody's getting some milk! How old? Well let me know if you need a refill on that sprite you've got there because I have been where you are my first daughter would have camped out all day on the boob if I'd have let her..." and we had a nice chat.

that's my advice on how to not make it weird. even a quick nod and a "I miss those days!" (or... "I don't miss those days!" depending on your situation) opens the door and sets the context and provides a reason for why you just can't look away.


Fri Jun 12 4:01 PM by spacefem in Pregnancy & Parenting

Thanks! I was going to put my labor story in Random but never got around to it. I can try to do it soon - it's written out already so just a matter of editing.

Yes you must! I'm happy to hear from you, hope everything went and is going well :)

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.

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.

Diaper bags

Thu Jun 25 9:14 AM by Gnarlbanya in Pregnancy & Parenting

I really liked the look of the 2 in 1 bag at first, but then I thought about all the junk in it that I'd have to strew all over the floor in order to make space for bub in the carry cot, so perhaps not a good idea on reflection. I'm pretty happy with the idea of using a clutch, but my husband really wanted a bag, mostly so that we could pretty much keep it packed and ready to go rather than spending fifteen minutes grabbing stuff every time we want to leave the house. This seemed like a good point, so we bought something cheap with loads of pockets. Will see how much we end up using it.

Can't find my tribe

Fri Jun 5 10:41 AM by maya in Pregnancy & Parenting

The title to your post reminded me of the ending for my novel I'm working on. "Tribe of one?" "Two." her friend corrects her, is as far as I got, LOL. It's hard for lots of people these days to find their 'tribes' in many different areas, mainly dealing with values that differ from the mainstream paradigm. It's even harder, I can only imagine, when children are involved. I don't have children but both my sisters and a few of my friends do, and it's heartbreaking sometimes, how other people react. I think places like baby yoga could also be good for meeting like-minded parents, but gender biases can show up more strongly in people if they think they are protecting their children by making them 'fit in'. Good luck, I hope you find a like-minded community of parents soon! :)

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).