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

[ Survey Results Intro | All Charts | Take the survey ]

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 0.2 0 0 3 3
247 3 0.1 3 0.2 1 1
248 15 0.3 3 0.2 1 1
249 12 0.2 3 0.2 2 2
250 14 0.3 3 0.2 1 1
251 11 0.2 3 0.2 2 2
252 20 0.4 6 0.4 0 0
253 17 0.3 2 0.1 0 0
254 15 0.3 9 0.6 1 1
255 29 0.6 4 0.3 1 1
256 17 0.3 9 0.6 1 1
257 14 0.3 11 0.8 1 1
258 23 0.5 5 0.4 2 2
259 37 0.7 13 0.9 2 2
260 35 0.7 6 0.4 1 1
261 31 0.6 9 0.6 4 4
262 58 1.1 9 0.6 3 3
263 56 1.1 17 1.2 3 3
264 44 0.9 17 1.2 2 2
265 69 1.4 20 1.4 3 3
266 72 1.4 25 1.8 2 2
267 73 1.4 19 1.3 1 1
268 70 1.4 20 1.4 2 2
269 100 2 30 2.1 5 5.1
270 121 2.4 34 2.4 1 1
271 106 2.1 31 2.2 1 1
272 128 2.5 50 3.5 1 1
273 156 3.1 46 3.2 2 2
274 148 2.9 32 2.3 1 1
275 155 3.1 46 3.2 4 4
276 177 3.5 62 4.4 4 4
277 209 4.1 60 4.2 1 1
278 219 4.3 57 4 1 1
279 248 4.9 64 4.5 1 1
280 254 5 73 5.2 1 1
281 269 5.3 61 4.3 1 1
282 214 4.2 77 5.4 1 1
283 231 4.6 52 3.7 5 5.1
284 217 4.3 46 3.2 2 2
285 215 4.2 55 3.9 1 1
286 205 4.1 70 4.9 4 4
287 206 4.1 58 4.1 1 1
288 160 3.2 33 2.3 1 1
289 126 2.5 41 2.9 1 1
290 117 2.3 40 2.8 1 1
291 106 2.1 14 1 1 1
292 59 1.2 27 1.9 2 2
293 57 1.1 10 0.7 1 1
294 41 0.8 12 0.8 7 7.1
295 13 0.3 7 0.5 1 1
296 17 0.3 5 0.4 2 2
297 9 0.2 1 0.1 1 1
298 6 0.1 3 0.2 1 1
299 5 0.1 0 0 1 1
300 3 0.1 0 0 1 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?
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.


Tue Oct 6 3:16 AM by Sassquatch in Pregnancy & Parenting

^ Why did the doctor tell you to forbid visitors who haven't had the vaccine? If you've had the vaccine then you're protected, so it's irrelevant if people bring the virus around.

As you stated above, you understand immunology, so I'm certain you then understand that vaccines don't provide protection at rates of 100% and that a newly immunized person may not have had sufficient time to develop antibodies. Additionally, the infant, the one most in need of protection, hasn't yet been vaccinated.

medicated vs. unmedicated birth

Mon Oct 5 6:47 PM by rowan in Pregnancy & Parenting

I had a plan to have an unmedicated birth, and then I had a 4 hour labor which was REALLY FREAKING INTENSE particularly in transition and I was crying and I'm pretty sure I whimpered "I can't do this" and the nurses were great and so was my husband, but by the time I was like GIVE ME THE FUCKING MEDICATION they couldn't because I had an issue with ...uh something? and they needed to do some bloodwork first to make sure it was ok and then it was too late because I actually was in transition and they don't do that when you hit that point.

Also she got stuck and had to be forceps-ed out.

Moral of the story: if there's any blood work or pre stuff you need done before medication, even if you think you don't want that medication, get the stuff done *before* things get intense. Just in case.

Letting kids use knives (and other dangerous implements)

Mon Sep 28 8:51 PM by ablotial in Pregnancy & Parenting

We didn't have knives at home until I was ... 9 or 10? But they gave us butter knives with school lunch right from the get go, so ... yeah. I never complained about this at home though because I was lazy and liked to be pampered and have my mom cut up my food and spread the butter for me :P

And I did have trouble when they finally gave me real (actually sharp) knives. Steak knives were fine because they were serrated, but I had trouble with paring knives telling which side was the sharp side and often used them upside down trying to saw through something with the dull edge. I finally learned to look closely and learn the difference when my dad got frustrated with how slow it was going for me and slammed his hand down on the knife to push it through (a carrot? celery? can't remember now) and almost cut off his thumb :/

What do you wish you had known?

Fri Sep 18 3:14 PM by rowan in Pregnancy & Parenting

Hm. I dunno, I don't really feel quite as terrified about things as I did for the first several years. Which isn't to say there aren't moments...

Prenatal genetic testing

Thu Sep 17 9:08 AM by rowan in Pregnancy & Parenting

MOD HAT: I have moved the vaccination discussion to a new thread. Please discuss vaccines there.

hospital vs homebirth

Tue Oct 6 3:07 AM by Sassquatch in Pregnancy & Parenting

The numbers don't lie. Home birth is several times riskier. For myself, being a risk averse type, I wouldn't choose it (even if I lived in a place where midwifery was licensed and part of the health care system.)

I'm not a fan of the fearmongering from birth woo proponents. I had a perfectly fine, no intervention, almost unmedicated hospital birth where my biggest complaint was actually not getting treated enough like a patient. Birth may indeed be a natural process, but it's the most demanding and traumatic natural process our bodies routinely undergo, and there's nothing wrong with treating it as a medical situation, because it is -- its a very significant, acute deviation from the normal everyday operation of our bodies. There's nothing shameful or harmful about acknowledging that,

Real stats for C-Sections?

Sun Oct 4 2:18 AM by Gnarlbanya in Pregnancy & Parenting

Thinking about this topic a little more, I think it's important that we remember that statistics just indicate trends and don't actually tell much of a story as far as individual circumstances go. By that I mean that while in some countries the c-section rate is statistically higher than in other places, it doesn't mean that an individual's decision to have a c-section in those countries is necessarily a flawed one. Nor does it mean that all doctors in those countries are scalpel-happy and just want to get babies out so they can take off to play golf or go for lunch, as I've seen it put on other pregnancy forums (not here).

If I do a brief statistical analysis of friends/acquaintances etc who have given birth in the last few years, the majority had vaginal births, everything from quick and uncomplicated to lengthy and forceps delivery. I can't think of any who had c-sections as a personal choice rather than for a medical reason. Those who had c-sections either had scheduled ones for good reason (obstruction due to fibroids, placenta previa, breech after unsuccessful ECV) or an emergency one for good reason (pre-eclampsia, fetal distress, placental abruption etc). Australia apparently has a c-section rate of 20-25% which this sample would accord with. But given the reasons for the c-sections, I do wonder when I read that the WHO recommends a c-section rate of 10-15%, who exactly should have been turned away from this limited sample?

Red Raspberry Leaf capsules - ever helpful for labour or hokum?

Mon Sep 28 3:19 PM by artemiscuous in Pregnancy & Parenting

Oh, this is an interesting discussion and one that I'm finding interesting as I am in the early stages of my second pregnancy.

I really appreciate both perspectives represented here - of modern medicine and of herbalism - and I actually like a middle way of using both, insofar as they are meant to be used (I think both can be and often are misused and misunderstood). I think a well-studied use of herbal remedies can be very complimentary to good medical care. A friend of mine, who is a Western herbalist and clinical researcher, is very evidence-based and really changed my perspective on the place for herbs. It's easy for people to go overboard and claim too many benefits to herbal remedies, to push baseless hokum like homeopathy and chakra balancing, etc., and it's equally easy to denounce it all as unproven, because most clinical studies are not looking at herbs in a double-blind, well-constructed study, particularly in pregnancy, because of the risks if it is somehow dangerous (and many herbs can be, just because they can be quite potent, particularly in a tincture or other concentrated form).

public service announcement: eating lunch with your friend who's a new mom

Fri Sep 18 10:27 AM by Nachos in Pregnancy & Parenting

I honestly love holding other people's babies while they're eating. Did this for a new mum friend who needed to go to the loo and she turned back a few times because the baby was crying, but as soon as she was out of sight, baby was just fine.

let's discuss childhood injuries

Thu Sep 10 3:19 AM by DarkOne in Pregnancy & Parenting

When I was about 7 or 8 I was riding my bike and rode off the curb, flew off the seat, landed on the tube, and somehow managed to get a cut in my vaginal area. Apparently, it bled like a mofo. It turned out to be only a small cut, but I can only imagine what my mom felt like when her 8yo showed up at her door crying hysterically and bleeding profusely from her crotch.

OMG, twins! Advice & thoughts?

Mon Oct 5 6:53 PM by rowan in Pregnancy & Parenting

From watching my friends with twins, I guess the hardest thing is the sleeping. They might not wind up on the same sleep schedule and then they might wake each other up with crying. So uh.... yeah.

I think for twins just plan on more of everything - more diapers, more clothes (anything interchangable is good) etc. I think the "stuff" angle is true for pretty much anyone, you don't need as much as you think (but more with twins). I used to have a list but the site I kept it on disappeared suddenly. :(

Altering my mind about pregnancy

Mon Sep 28 9:09 PM by ablotial in Pregnancy & Parenting

My mom was 39 when I was born and 42 when my younger brother was born both naturally with no drugs or complications, and both of us were healthy and happy. The only thing I will say is my mom was noticibly "less fun" (read: less energy) than my friends' moms, who were often in their early-to-mid 30s when my mom was 50.

As others have mentioned though, there is this (overblown) line in many minds about age 35, so they will probably want to monitor the crap out of you. And there is a bit of a higher risk for chromosomal problems, like Downs. But if you are ok with that and unlikely to have a super early menopause, I say you know yourself best and it is better to wait until you are at a point where you are capable and mentally ready to support a baby. 40s are definitely not too late!

that time I got food poisoning when I was pregnant

Sat Sep 19 12:34 PM by spacefem in Pregnancy & Parenting

We have topics and questions all the time about what to eat when you're pregnant, so I wanted to share this charming story of an experience I had while pregnant with my second daughter.

I was only 10 or 11 weeks along and had been dealing with a "managable" level of morning sickness. This means that I could throw up at any time without warning, but in a cute pregnant way, not a dibilitating one. Most times, as long as there was food on my stomach I'd be okay, so I was careful to keep healthy snacks around - my favorite being cheetos, because you know, cheese is dairy right?

I was following all the good internet advice of not eating raw or uncooked foods, no deli meat, no salad bars, no soft cheeses, only low mercury fish, no food out of trunks of cars, etc.

We went to a wedding at a nice hotel. There was a buffet. I was one of the first people in line at the buffet because I had a two year old who looked like she might be hungry so I played that card, you know how it is. The food was delicious - salad with fresh lettuce, rice, beef strogonoff, mixed veggies. Everything that was supposed to be cold was cold and everything that was supposed to be hot was steaming hot.

sleep deprivation

Thu Sep 17 3:26 PM by robichek in Pregnancy & Parenting

Apparently there is a new book out called The Rabbit Who Wants to Go to Sleep and it is ALL THE RAGE.. http://www.amazon.com/Rabbit-Wants-Asle ... 149617951X

If you are still breastfeeding, that may be an issue (not that I recommend that you stop breastfeeding). Topping up before they sleep could be warranted.

For my kid, we keep his room permanently dark and have a white-noise soundmaker outside his door and it works well. Also, although we didn't do a pure "cry it out" method, there were times at the beginning of his "sleep through the night" nights that he would wake up and whimper and we just would wait 2-10 minutes and he'd go back to sleep. That went away and now we don't expect a peep until at least 11 hours have passed. I think we as worried mothers are sort of complicit in creating their "need" for us.. If my boy knows I'll come in within 30 seconds of him making a sound, he'll want me to come in. If he's not sure how long it'll take, he'll go back to bed... Please take the preceding advice as something I might recommend only after the kid is 1 year old. Before then I would never just let him be... I used to rock him to sleep until my arms gave out.

non-religious parents raise okay kids after all

Wed Sep 2 3:37 AM by AndrewZealand in Pregnancy & Parenting

However, one thing I remember clearly from my childhood is being very afraid of death.

I remember when I first realized that we die when we get old. I told my best friend at the time and he got really upset. I never quite had the need for an afterlife, though I remember at about 10 I conceived that when we died maybe we came back again as someone else. This was before I knew that someone else had already thought of that :P

Presently I'm still open to the idea of some sort of afterlife when we die. One thing I find inspirational when I'm depressed is the thought that there might be some sort of new and interesting afterlife when we die. It can give me energy to keep on with this life. But the idea of eternal punishment for our sins in the afterlife? I'd say to the average man that's the same as "Life's a bitch and then you die and then you go to hell and suffer". The idea that we MIGHT get punished for our sins when we die, for most of us, only serves to make our lives more fearful and miserable and then of course when we die we may well find that no such punishment exists. Like the saying goes "Cheer up, it might never happen". The only usefulness I think of for the idea of afterlife retribution, is something with which to scare a tyrant who is so powerful that apparently nothing in this life can stop him or her abusing people and nature. By telling them that there might be something in the afterlife holding them to account, you might actually scare them into reconsidering their behaviour. But I'd say that for most people, hell or other afterlife punishment, is an unnecessary fear.