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
0585039W,5D
1162939W,5D
29138W,6D

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 0.2 1 1.1
246 13 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 4 0.2 2 2.2
250 15 0.3 4 0.2 2 2.2
251 13 0.2 3 0.2 2 2.2
252 22 0.4 6 0.4 1 1.1
253 20 0.3 3 0.2 0 0
254 17 0.3 9 0.6 1 1.1
255 29 0.5 4 0.2 1 1.1
256 18 0.3 9 0.6 1 1.1
257 16 0.3 11 0.7 1 1.1
258 26 0.4 5 0.3 2 2.2
259 41 0.7 15 0.9 2 2.2
260 38 0.6 12 0.7 1 1.1
261 43 0.7 10 0.6 4 4.4
262 61 1 10 0.6 4 4.4
263 61 1 18 1.1 3 3.3
264 52 0.9 19 1.2 2 2.2
265 77 1.3 24 1.5 3 3.3
266 87 1.5 28 1.7 2 2.2
267 81 1.4 24 1.5 1 1.1
268 79 1.4 24 1.5 2 2.2
269 111 1.9 35 2.1 1 1.1
270 135 2.3 39 2.4 1 1.1
271 115 2 35 2.1 1 1.1
272 148 2.5 54 3.3 1 1.1
273 180 3.1 50 3.1 2 2.2
274 168 2.9 40 2.5 1 1.1
275 184 3.1 52 3.2 4 4.4
276 215 3.7 72 4.4 4 4.4
277 240 4.1 68 4.2 1 1.1
278 245 4.2 63 3.9 1 1.1
279 288 4.9 74 4.5 1 1.1
280 321 5.5 90 5.5 1 1.1
281 322 5.5 76 4.7 1 1.1
282 254 4.3 84 5.2 1 1.1
283 272 4.6 60 3.7 5 5.5
284 245 4.2 54 3.3 2 2.2
285 245 4.2 63 3.9 1 1.1
286 232 4 79 4.8 1 1.1
287 246 4.2 64 3.9 1 1.1
288 185 3.2 38 2.3 1 1.1
289 146 2.5 42 2.6 1 1.1
290 133 2.3 47 2.9 1 1.1
291 115 2 14 0.9 1 1.1
292 69 1.2 34 2.1 3 3.3
293 67 1.1 12 0.7 1 1.1
294 47 0.8 13 0.8 1 1.1
295 13 0.2 8 0.5 1 1.1
296 18 0.3 6 0.4 2 2.2
297 15 0.3 3 0.2 1 1.1
298 6 0.1 3 0.2 1 1.1
299 5 0.1 1 0.1 2 2.2
300 5 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
Charts generated by flot
spacefem.com
spacefem@spacefem.com

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.

How NOT to help parents with a newborn

Wed Jun 29 8:26 AM by codingchemist in Pregnancy & Parenting

Don't overstay your welcome! Bring food (preferably something that is easily frozen and can be taken out in single servings), comment on how absolutely adorable the baby is, and when the baby starts screaming, be prepared to make your exit.

And ditto on bringing your unruly kids over-I don't want your crazy 5 year old holding my newborn baby.

I'm expecting my 2nd baby very soon-I'm sure I'll have a lot more to add to this list in a few weeks :rainbowsmile:


minimalist kids birthday parties

Sun May 15 9:19 PM by melsbells in Pregnancy & Parenting

For the first two birthdays, we tried to make some special food and splurge on interesting fruit. If I lived closer to friends, I would want to throw a get-together as an excuse to see my friends, celebrate our survival of another year. I don't think my kid would actually be into that though. They are turning out to be quite introverted and shy.


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.


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....


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.


it gets better thread for parents

Mon Jun 13 11:16 PM by rowan in Pregnancy & Parenting

Sometimes I think they go through a growth spurt or something weird-ass like that and then when it's done it gets better again. But who knows, kids are weird. It will get better again. We seem to be having night terrors again though not as badly as before. Those seem to correlate with growth spurts (for us). They are tailing off again so hopefully...?


Pregnancy Guidebooks for Cool Moms (humor)

Wed May 11 3:39 PM by rowan in Pregnancy & Parenting

One of my friends is part of this magazine. She didn't write this one but it's pretty hilarious.

http://theoffingmag.com/wits-end/pregna ... cool-moms/

Anyone want to come up with our own "Guidebook" titles?

spoiler:
the one about inducing labor by setting your hair on fire is my favorite


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.


Criminalization of drug use during pregnancy to end in Tennessee

Tue Mar 29 2:48 AM by Amuro in Pregnancy & Parenting

Actually I think it would be better if the penalty was rehab and being sent to a therapist. It's pretty dumb to criminalize it especially because there is an almost certainty custody will be taken away. Why not try and fix the problem with addiction so there is less of a strain on social services. There should be increased awareness but what idiot doesn't know drugs are bad for you and worse if your pregnant. If you are addicted to drugs you obviously are thinking about getting high and that's about it.


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?


Kids are full of LIES

Sun May 22 2:29 PM by rowan in Pregnancy & Parenting

Don't be silly monk, everyone knows a good conglomerate goes better with milk


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.


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.


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.