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 12 0.2 5 0.2 1 1.1
246 16 0.2 1 0 3 3.2
247 9 0.1 4 0.2 1 1.1
248 18 0.2 3 0.1 1 1.1
249 17 0.2 4 0.2 2 2.1
250 17 0.2 5 0.2 2 2.1
251 17 0.2 3 0.1 2 2.1
252 32 0.4 9 0.4 1 1.1
253 25 0.3 3 0.1 1 1.1
254 22 0.3 11 0.5 1 1.1
255 33 0.4 7 0.3 1 1.1
256 19 0.3 9 0.4 2 2.1
257 23 0.3 12 0.6 1 1.1
258 34 0.5 10 0.5 1 1.1
259 57 0.8 18 0.9 2 2.1
260 49 0.7 14 0.7 1 1.1
261 52 0.7 16 0.8 4 4.2
262 73 1 14 0.7 1 1.1
263 77 1 22 1.1 3 3.2
264 68 0.9 24 1.2 4 4.2
265 93 1.2 25 1.2 4 4.2
266 110 1.5 36 1.8 1 1.1
267 99 1.3 27 1.3 1 1.1
268 110 1.5 31 1.5 2 2.1
269 141 1.9 47 2.3 1 1.1
270 187 2.5 51 2.5 1 1.1
271 162 2.2 47 2.3 1 1.1
272 175 2.3 64 3.1 1 1.1
273 232 3.1 67 3.3 3 3.2
274 228 3 48 2.4 1 1.1
275 225 3 62 3 5 5.3
276 276 3.7 92 4.5 5 5.3
277 305 4.1 80 3.9 1 1.1
278 309 4.1 77 3.8 1 1.1
279 356 4.8 89 4.4 1 1.1
280 435 5.8 121 5.9 1 1.1
281 414 5.5 99 4.9 1 1.1
282 326 4.4 106 5.2 1 1.1
283 327 4.4 82 4 1 1.1
284 309 4.1 67 3.3 2 2.1
285 322 4.3 73 3.6 1 1.1
286 308 4.1 95 4.7 1 1.1
287 307 4.1 76 3.7 1 1.1
288 254 3.4 50 2.5 2 2.1
289 178 2.4 57 2.8 1 1.1
290 167 2.2 59 2.9 1 1.1
291 145 1.9 16 0.8 2 2.1
292 86 1.1 38 1.9 3 3.2
293 88 1.2 15 0.7 2 2.1
294 54 0.7 16 0.8 1 1.1
295 18 0.2 13 0.6 1 1.1
296 20 0.3 6 0.3 2 2.1
297 15 0.2 6 0.3 2 2.1
298 8 0.1 3 0.1 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
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.

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).

Just Can't Let It Go

Wed Jul 26 1:18 AM by Taurwen in Pregnancy & Parenting

We didn't find out specifically because we didn't want a lot of pink stuff if it was a girl.

Somehow MIL has still given us a ton of pink clothing that she'll change him into everytime she comes over.

I hate pink.

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.

Happiest Baby on the Block

Wed Jul 12 4:52 PM by antfancier in Pregnancy & Parenting

My mum gave me 'Your Baby and Child' by Penelope Leach, which is what she used when she had me. It covers from birth to five years. I read the first section about newborns in preparation. After having the baby, I realised I have zero time or brain power to do anything so I never got around to the rest of it. In general, I liked the book though. It's a simple overview and has nice color photos.

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. ;)

Another baby stars

Thu Jun 15 6:54 AM by StarsInUrEye in Pregnancy & Parenting

Thanks for the congratulations and encouragement.

I had an appointment with the obgyn today. He seems to think I'm even farther along than he originally thought. I didn't have an ultrasound. He just went by the size of my uterus. It's well over my belly button now. He's sending me to a high risk Dr. Asap and then I'm suppost to see him again on the 29th. By then he said they will have a better idea as to how far along I actually am. So far the pregnancy is going well. I did have complications with my first one and went to a specialist but this time I'm being referred to one because I'm old lol. They automatically send women when they are 35 and older.