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 14 0.2 5 0.2 1 1
246 17 0.2 1 0 3 3.1
247 10 0.1 4 0.2 1 1
248 18 0.2 3 0.1 1 1
249 17 0.2 4 0.2 2 2.1
250 17 0.2 5 0.2 1 1
251 17 0.2 3 0.1 2 2.1
252 33 0.4 9 0.4 1 1
253 25 0.3 3 0.1 1 1
254 22 0.3 11 0.5 1 1
255 33 0.4 7 0.3 1 1
256 21 0.3 9 0.4 2 2.1
257 24 0.3 12 0.6 1 1
258 35 0.5 10 0.5 1 1
259 58 0.7 20 0.9 2 2.1
260 49 0.6 14 0.7 1 1
261 52 0.7 17 0.8 4 4.1
262 73 0.9 14 0.7 1 1
263 79 1 23 1.1 3 3.1
264 70 0.9 25 1.2 4 4.1
265 95 1.2 25 1.2 4 4.1
266 115 1.5 36 1.7 1 1
267 106 1.4 27 1.3 1 1
268 115 1.5 31 1.5 2 2.1
269 146 1.9 50 2.4 1 1
270 190 2.4 53 2.5 1 1
271 168 2.2 50 2.4 1 1
272 184 2.4 68 3.2 1 1
273 242 3.1 68 3.2 3 3.1
274 232 3 50 2.4 1 1
275 234 3 63 3 6 6.2
276 285 3.7 95 4.5 6 6.2
277 311 4 82 3.9 1 1
278 320 4.1 82 3.9 1 1
279 368 4.7 93 4.4 1 1
280 455 5.9 125 5.9 1 1
281 429 5.5 103 4.9 1 1
282 341 4.4 108 5.1 2 2.1
283 334 4.3 86 4.1 1 1
284 321 4.1 70 3.3 2 2.1
285 342 4.4 75 3.5 1 1
286 318 4.1 98 4.6 1 1
287 327 4.2 83 3.9 1 1
288 259 3.3 55 2.6 2 2.1
289 187 2.4 60 2.8 1 1
290 175 2.3 62 2.9 1 1
291 153 2 16 0.8 2 2.1
292 91 1.2 38 1.8 3 3.1
293 92 1.2 16 0.8 2 2.1
294 56 0.7 19 0.9 1 1
295 20 0.3 14 0.7 1 1
296 20 0.3 7 0.3 2 2.1
297 15 0.2 6 0.3 2 2.1
298 8 0.1 3 0.1 1 1
299 7 0.1 1 0 2 2.1
300 7 0.1 1 0 2 2.1

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?
Download the data
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
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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.

housemates + newborn = ?

Wed Jul 18 6:31 PM by octarineoboe in Pregnancy & Parenting


I admit I haven’t been around here a ton lately but I didn’t know babySonic had arrived! Congrats!!!!

Alas I don’t have any actual advice. My college besties (a married couple) and I fantasize about sharing a house, and they are actively trying to have kids, so we talked about that possibility a little bit, but right now we live in different cities and they don’t have a kid yet so it’s all speculation. But I think it could probably work - as the prospective non-parent I would want to make sure I had my own kid-free space in the house and we were really clear about responsibilities ahead of time, eg, I’m a roommate not an all-purpose babysitter, how will this affect the split of other housework, etc.

My Ectopic Pregnancy

Tue Jan 23 8:47 PM by rowan in Pregnancy & Parenting

FYI we have a general culture in the pregnancy forum here about sharing similar stories as a way to offer support, and also about giving any medical knowledge that we've come across, since pregnancy is generally not talked about as much as it should be and you find information in random places. Since you haven't been around until now you probably didn't know that, and mels' post is well in line with forum guidelines and norms. Please don't go all mod martyr on us now that you're only just back. This is me as a friend speaking here, not with my modhat on.

I'm sorry for your loss. Ectopic pregnancies are scary, and I would like to go punch that first doctor in the face for you.

PPD is awful too. :( I hope you can get through it.

gender recognition

Thu Nov 2 1:03 PM by Nech in Pregnancy & Parenting

You can continue discussing with him the difference of a boy and a girl. Have him socialize too with the same gender. There's nothing wrong if you have go with opposite sex as long as he understands what/who he is.

So do you feel hanging out with the opposite gender at a young age can confuse a person's gender identity?

leftist parenting and gender [split from gender recognition]

Sat Sep 23 11:52 AM by Unvoiced_Apollo in Pregnancy & Parenting

gender recognition.">

If a boy who has a penis asks if he's a boy and you don't just say yes, then that's straight up lunacy.

What he decides to do with that boyhood or how he dresses is up to him. But if you're born with a penis you're a boy.

Making it airy fairy when, statistically, scientifically, less than 1% of 1% of children born have true gender dysphoria, is immoral and wrong. It's also a sign of our troubled times.

This is just my anecdotal experience but...

I have experienced bullying based on simply engaging in normal children's play with girls. Insults were attacks on both me and the girls. But I NEVER questioned my gender as a male. So if a child asks me if he's a boy and was identified biologically as one, I am going to question what influences are on the child before I answer.

Postpartum issues: things that can go wrong after

Wed Aug 9 5:24 PM by rowan in Pregnancy & Parenting

ugh that totes doesn't just happen during c-section. I had a friend who found out when she was having (other) surgery years later and they stitched her up since "they were in there anyway". Honestly I think I also have it but it doesn't cause problems *most* of the time (sometimes stabby pain but no one takes it seriously so idk).

Unplanned, polyamorous pregnancy situation

Sun Apr 29 12:18 PM by metawidget in Pregnancy & Parenting

I'm glad you have been communicating and working things out. I wish you lots of health and love as you wrote the next chapter of this story.

I might be pregnant...

Fri Jan 5 3:16 AM by Aum in Pregnancy & Parenting

Aum, my partner and I were just discussing this. He was surprised by my taking the hard line that stopping BC or poking holes in condoms or something like that is rape, making the woman a rapist. Which should result in jail time, so she should lose custody, which should go to the father and now he has the choice of keeping the baby or putting them up for adoption.

It's unfortunate that you can't prove such a thing, but hopefully if it was actually taken seriously women would be less likely to do it because it would at least be explicitly called rape.

I understand how the justice system and the family courts would look at it. They see it as the man's sperm made it to the egg so somehow he wasn't protecting himself, he made the choice, yada yada. There's no way to prove that the woman was manipulative, withdrew BC, or "poked holes in the condom" (I think that's unheard of, but anyway).

When do you outsource parenting?

Sat Oct 14 7:47 PM by rowan in Pregnancy & Parenting

yeah I do a ton of supplemental history... :(

It might be time for a baby.

Sat Sep 16 1:59 PM by Sonic# in Pregnancy & Parenting

I got curious on the question of single parent families. Definitely, I think financial stability or having some sort of support network (family, friends) is better than not having it.

I found this article ( https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4886836/ ). The article does point out that several factors adjust child adjustment, like finances and parental stress. Merely being a single parent? Not a factor:
The findings suggest that solo motherhood, in itself, does not result in psychological problems for children.

The lit review at the beginning of the article adds some specificity here. What seems hard on kids is not single parenthood itself; it's often the divorce that results in a single parent being involved. These studies have consistently shown that children whose parents divorce are more likely to show emotional and behavioral problems than are children in intact families (Amato, 2000, 2001, 2005; Coleman & Glenn, 2009; Hetherington & Stanley-Hagan, 1999; Pryor & Rodgers, 2001). However, the children’s difficulties appear to be largely associated with aspects of the divorce, rather than single-parenthood, in itself. Then there are people who become single parents, but not by choice. That's also rough, often because these parents lack the financial stability and stability to do well. So the article is really looking at single parents by choice. They can raise children as well as two-parent households.

How to deal with opinionated toddlers (or babies or kids)

Tue Aug 1 1:57 AM by rowan in Pregnancy & Parenting

Ooof. My kid is very social, needs to be around someone all the time. It's ... challenging, as you've found. It does get better as they gain their own interests. But it took a long time to get past clingy.

Not having read your post, but just the heading, my response was "wine." But after reading your post, I thought "wine."

Yes. After bedtime.

Also, honestly the only way we made it through was we would take turns being the center of focus. We still do this, divide and conquer (and she's only one kid, hell). Also, I know people are like really limit screen time BUT if you really need to get something done one episode of e.g. Daniel Tiger or Paw Patrol or whatever isn't gonna be too bad. I think DarkOne has some good ideas too.

Good luck.

posting pictures of kids and privacy

Wed Apr 25 7:29 AM by juliabonl17 in Pregnancy & Parenting

Usually, we don't share photos of our children in social media. Sometimes I can send some photos to close friends. I keep my personal life in quiet. Share with family only.

I had my 2nd baby!!!!

Wed Jan 3 8:21 PM by MFS in Pregnancy & Parenting


I am still dealing with the fact that your 11 year old is an actual 11 year old.

on being semi-pregnant

Tue Oct 3 7:18 PM by geldofc in Pregnancy & Parenting

congratulations!! i've never been pregnant but i'm jealous. i'm having baby fever lately.


Wed Sep 13 6:58 PM by geldofc in Pregnancy & Parenting

my clock started ticking in my 20s and i would love a child at 30 now but i want to live how i want for a few more years, and have my career established. i don't see parenthood for another 5 years.

egg freezing seems like a good option esp if you have extra time and money.

bad reasons for having a baby

Tue Aug 1 1:47 AM by rowan in Pregnancy & Parenting

but I take them to restaurants so I know they end up hating 90% of the things they ask for.

- kid would like a sibling

- maybe people are right about end of life stuff

That's about it. I hated being pregnant, the last time I was pregnant the hormones were... really awful. Plus kid is now pretty big so another one would be weird and we gave away all our stuff. ;)