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 0.1 4 0.3 1 1.1
246 12 0.2 1 0.1 3 3.3
247 5 0.1 3 0.2 1 1.1
248 16 0.3 3 0.2 1 1.1
249 13 0.2 3 0.2 2 2.2
250 14 0.2 4 0.3 2 2.2
251 13 0.2 3 0.2 2 2.2
252 22 0.4 6 0.4 0 0
253 20 0.4 3 0.2 0 0
254 17 0.3 9 0.6 1 1.1
255 29 0.5 4 0.3 1 1.1
256 17 0.3 9 0.6 1 1.1
257 16 0.3 11 0.7 1 1.1
258 25 0.4 5 0.3 2 2.2
259 40 0.7 14 0.9 2 2.2
260 37 0.6 12 0.8 1 1.1
261 39 0.7 9 0.6 4 4.4
262 60 1.1 9 0.6 4 4.4
263 60 1.1 18 1.1 3 3.3
264 52 0.9 19 1.2 2 2.2
265 76 1.3 24 1.5 3 3.3
266 83 1.5 28 1.8 2 2.2
267 80 1.4 24 1.5 1 1.1
268 79 1.4 24 1.5 2 2.2
269 110 1.9 34 2.1 1 1.1
270 132 2.3 35 2.2 1 1.1
271 115 2 33 2.1 1 1.1
272 141 2.5 52 3.3 1 1.1
273 176 3.1 50 3.1 2 2.2
274 163 2.9 40 2.5 1 1.1
275 179 3.1 51 3.2 4 4.4
276 211 3.7 68 4.3 4 4.4
277 232 4.1 67 4.2 1 1.1
278 241 4.2 61 3.8 1 1.1
279 280 4.9 73 4.6 1 1.1
280 305 5.4 85 5.3 1 1.1
281 310 5.4 71 4.5 1 1.1
282 241 4.2 84 5.3 1 1.1
283 266 4.7 58 3.7 5 5.6
284 241 4.2 54 3.4 2 2.2
285 241 4.2 63 4 1 1.1
286 229 4 78 4.9 1 1.1
287 237 4.2 61 3.8 1 1.1
288 182 3.2 37 2.3 1 1.1
289 143 2.5 42 2.6 1 1.1
290 132 2.3 47 3 1 1.1
291 114 2 14 0.9 1 1.1
292 68 1.2 34 2.1 3 3.3
293 65 1.1 12 0.8 1 1.1
294 46 0.8 13 0.8 1 1.1
295 13 0.2 8 0.5 1 1.1
296 17 0.3 6 0.4 2 2.2
297 13 0.2 2 0.1 1 1.1
298 6 0.1 3 0.2 1 1.1
299 5 0.1 1 0.1 2 2.2
300 4 0.1 1 0.1 1 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
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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.

young kids, consent and bodily autonomy

Mon May 2 8:46 PM by monk in Pregnancy & Parenting

I think it depends on the child. Do you ask a newborn if it needs it's diaper changed? Obviously no. Do you help a 13 year old get dressed? Obviously no. Somewhere in there the child matures to the point where they should learn that they own their bodies even if they don't have all the privileges an adult does. This age is going to vary wildly between different children (by widly, I would say 3 year range). I would guess that some kids might be ready for this lesson as early as 3 while others not until they're about to go school. Actually that's a pretty good benchmark, because if you're going to put them in a group with other kids they don't know they should know the rules about touching or being touched.

As far as kissing Grandma, maybe they shouldn't have to do it, but making them do this social communcation helps get them ready for all the other social communication that will be forced on them later. Plus, grandma needs that love to help HER be healthy.

Criminalization of drug use during pregnancy to end in Tennessee

Mon May 2 11:14 AM by Lia913 in Pregnancy & Parenting

That's good news! I believe a woman should stop taking drugs or drinking alcohol (or smoking) immediately after she had unprotected sex in case she's pregnant. And a woman can be pregnant even if she had sex during period. So, the actions of the authorities seem a necessary measure.

Umbilical cord

Wed Apr 27 1:26 AM by antfancier in Pregnancy & Parenting

There's a Bulgarian tradition about the umbilical cord my friend told me about. When the dried little stump falls off your baby, you're supposed to throw it in a place that reflects your child's future, or at least the future you want for them. My friend threw his first son's on to the pitch at a Yankees' game and for his second son he threw it at the stage during a concert!

When my son's cord fell off a few weeks ago, I put it on the counter next to his changing pad then promptly forgot about it. I've no idea where it is now.

Sperm Can be Cultivated from Skin Cells

Thu Mar 10 6:56 PM by rowan in Pregnancy & Parenting

Pretty sure this was a spam post but the post itself is kind of interesting. Maybe it could go to Sci & Tech, though it has relevance here as well. I added a link to the Science article, in case anyone wants to read it.

Advice on dealing with a sick baby

Mon Feb 22 5:28 PM by rowan in Pregnancy & Parenting

oh re: diaper rash, we found our kiddo was super sensitive and when things go really bad we got something prescribed from the doc that worked *wonders*. IDEK why that stuff isn't marketed, the pharmacist mixed it all up. The doc called it "poop goop" but I dunno what was in it.

7th Birthday - Theme Suggestion

Mon May 2 8:18 PM by melsbells in Pregnancy & Parenting

I met a kid about that age who had a geo-caching birthday party and another one who had a roller-skating party. Both sounded awesome. The first one sounded like a whole lot of work to put together.

Advice for surviving the last days of pregnancy?

Mon May 2 11:13 AM by Lia913 in Pregnancy & Parenting

Think about everything you would like to do with your child after birth. How you'll take care of the baby? Who will your baby look like? Think about breastfeeding, maybe (sorry that I suggested this topic if you're not going to BF): it has it's advantages, but it's still not for everyone. Or you can just read a good book! :)

test out my new name picker

Fri Apr 15 11:41 PM by rowan in Pregnancy & Parenting

my neighbor's dog is named Gunner? Makes more sense for a bird dog....

Why have children if you want to work (aka it's 1950!)

Tue Mar 8 9:16 PM by antfancier in Pregnancy & Parenting

I just had a look at your article. :thumbup:
As you say, many comments have been deleted, but that's probably for the best otherwise I'd get mad.

I'm about to have my first child and have had some similarly surprising responses from people when I explain I'm going to be a SAHM; everything from admiration to unsolicited suggestions that a nanny is better than daycare. When I explain that the reason is that I acut ally want to work but my earnings from my two part time jobs would barely cover childcare, it always gets awkward. And then they suggest the whole home daycare/nanny thing again. Even if I could afford it, I'd rather choose the daycare because they have facilities and resources that I don't (I live in a basement apartment, with pretty minimalist furnishings).

I get it. People have strong beliefs about what is 'best', but it's not a one-size-fits-all scenario. And holy crap! If a woman wants and is able to work after having kids, why on earth shouldn't she?

warning: when your baby sleeps through the night...

Fri Feb 19 3:18 AM by rowan in Pregnancy & Parenting

We didn't get the sleepwalking (thankfully) but demonic possession seems about right. It presented a lot like a horrible nightmare with very loud screaming/crying, but we couldn't wake her up from it. She wouldn't remember it at all in the morning, at least. We did find that sometimes we could 'interrupt' it by either singing or telling her stories about something completely random, but what was effective one night often was not effective the next so it was constantly trying something new. Over time the singing seemed to work better and better until they (mostly) went away, but it took a very long time.

I think the hardest was the feeling of complete helplessness to stop it. :( But like I said she never remembered any of it.

it gets better thread for parents

Mon May 2 3:57 PM by rowan in Pregnancy & Parenting

I'll come back to this but at 7 we are into feeding herself stage, she can get waffles out of the freezer and use the toaster and get her own cup of (water,milk,juice,etc) even out of the tall cupboards without dying.

Every year seems to get better (I imagine the teen years will reverse this statement)

stuttering at the end of words

Thu Apr 28 9:21 PM by Sonic# in Pregnancy & Parenting

I don't think it's a cause for immediate concern, but my experience would lead me to talk to a doctor about it. I didn't have a stutter when I was 2. I had language delay. I didn't learn language when kids typically do. Needless to say, I was a very frustrated little kid. When my parents and my pediatrician caught on to it, I had to spend a few years seeing a speech pathologist.

I've read that stuttering is at least partly psychological, but I really can't say more than that. If nothing else, I'd just want to know that his frustration is a necessary part of development like teething and not something that can be avoided.

Pets and newborns

Tue Mar 22 2:34 AM by codingchemist in Pregnancy & Parenting

It's really obvious that the dog is stressed out by the toddler and I'm worried about the times when the kid is showing too much interest in the dog and we're not paying enough attention.

Yeah-stressed out dogs can make for stressful times with toddlers. Toddlers just want to pet and hug, and don't want to listen to pleas to leave the dog alone. We wound up getting an automatic treat dispenser and giving the dog relaxation exercises behind a barrier. So now when the toddler is running the length of the house screaming, the dog can be behind the barrier staring lovingly at her treat dispenser, instead of trying to herd the kid. Of course, it isn't really feasible to keep the dog behind the barriers at all times, but at least it gives us some breaks.

Our behavioralist also recommended Prozac, which took a long time to get the dose right, but has helped the dog be less reactionary and neurotic.

Party For My Mom

Thu Mar 3 10:36 PM by curlybae in Pregnancy & Parenting

Hi! It's a great idea to throw a party for your Mom. So yeah, invite her good friends and those who she hasn't seen for quite some time already. Prepare some healthy food or you can get a caterer for this tell them to prepare your mom's favorite dishes. Set up a good sound system where they can opt to dance or sing their old fav songs. Request her friends to prepare a great birthday greetings and i'm sure she won't forget this event.

Flying while pregnant, Split from Cartoons for Little Girls in Feminism

Thu Feb 18 1:01 AM by trillianastra in Pregnancy & Parenting

Sassquatch, that's what I was wondering too! A friend who has three kids gave me some great advice about being pregnant. She said, "You're going to get advice from everyone. Feel free to ignore it unless it comes from your doctor!" (And she's a nurse, so for her to even exclude herself from the "advice-giving" permission list was crazy, IMO!)