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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
0414439W,5D
1118939W,5D
28739W,1D

Daily probabilities of spontaneous labor, by number of subsequent previous births

Day 0 previous births 1 previous birth 2 or more previous births
#% #% #%
245 7 0.2 1 0.1 1 1.1
246 12 0.3 0 0 2 2.3
247 3 0.1 2 0.2 1 1.1
248 12 0.3 2 0.2 1 1.1
249 6 0.1 3 0.3 1 1.1
250 11 0.3 1 0.1 1 1.1
251 8 0.2 3 0.3 1 1.1
252 17 0.4 5 0.4 0 0
253 15 0.4 2 0.2 0 0
254 13 0.3 8 0.7 1 1.1
255 24 0.6 4 0.3 2 2.3
256 14 0.3 7 0.6 1 1.1
257 12 0.3 11 0.9 1 1.1
258 22 0.5 2 0.2 2 2.3
259 26 0.6 12 1 1 1.1
260 28 0.7 6 0.5 1 1.1
261 26 0.6 6 0.5 4 4.6
262 52 1.3 6 0.5 3 3.4
263 47 1.1 14 1.2 1 1.1
264 38 0.9 15 1.3 2 2.3
265 59 1.4 16 1.3 2 2.3
266 58 1.4 18 1.5 2 2.3
267 62 1.5 16 1.3 1 1.1
268 50 1.2 17 1.4 2 2.3
269 85 2.1 27 2.3 5 5.7
270 104 2.5 29 2.4 1 1.1
271 92 2.2 30 2.5 1 1.1
272 103 2.5 40 3.4 1 1.1
273 128 3.1 37 3.1 2 2.3
274 128 3.1 26 2.2 1 1.1
275 120 2.9 36 3 4 4.6
276 155 3.7 57 4.8 2 2.3
277 164 4 52 4.4 1 1.1
278 181 4.4 50 4.2 1 1.1
279 209 5 51 4.3 1 1.1
280 211 5.1 65 5.5 1 1.1
281 226 5.5 49 4.1 1 1.1
282 182 4.4 67 5.6 1 1.1
283 189 4.6 45 3.8 3 3.4
284 178 4.3 36 3 2 2.3
285 177 4.3 46 3.9 1 1.1
286 158 3.8 58 4.9 3 3.4
287 165 4 51 4.3 1 1.1
288 118 2.8 27 2.3 1 1.1
289 96 2.3 30 2.5 1 1.1
290 85 2.1 34 2.9 1 1.1
291 86 2.1 11 0.9 1 1.1
292 49 1.2 25 2.1 2 2.3
293 53 1.3 7 0.6 1 1.1
294 31 0.7 11 0.9 7 8
295 10 0.2 7 0.6 1 1.1
296 15 0.4 4 0.3 2 2.3
297 7 0.2 1 0.1 1 1.1
298 5 0.1 2 0.2 1 1.1
299 5 0.1 0 0 1 1.1
300 1 0 0 0 0 0

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
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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.

How is pregnancy different from when it's shown in TV?

Thu Dec 18 10:48 AM by Aum in Pregnancy & Parenting

Not to mention the water doesn't usually break until active labor.


Visitors soon after birth

Sat Dec 13 6:21 PM by monk in Pregnancy & Parenting

My sister and her husband were glad for mine and our mothers help for limited periods when she just wanted to sleep but we both understood "the look" that said we should go away without her having to actually throw us out. If you don't have that relationship with "S" and can't establish it before the babies born don't guest her at your house.

But it is a really kind offer. Maybe she doesn't know you already have a support system? let her know.


Confessions of an Evil Stepmother

Thu Dec 11 1:15 PM by Nachos in Pregnancy & Parenting

I have no help, but I can offer hugs. *hugs*


Finding out baby's sex before birth

Wed Dec 3 3:54 AM by aka_laura in Pregnancy & Parenting

We found out, it was a fun detail to learn about our baby, it inspired the Wonder Woman nursery theme. My friends and family didn't go too nuts on the pink. There were a number of weird conversations with people who assumed I would oppose pink. I think pink is a lovely color for a baby to wear, alongside all the others, but people associated feminism with some kind of anti-pink venom that I just don't feel. I guess I feel like eventually, my family and friends are going to know the kid's sex. Our culture will ascribe gender roles to her far before she's conscious of them herself, so she'll have to be taught from a very young age that such things are bullshit. Wether she starts being gendered at 3 months or 3 days doesn't stand to change things significantly, in my view, we still have a long road on that one.


Pregnancy Books

Sun Nov 30 2:38 PM by Metcodon1 in Pregnancy & Parenting

For a good pre-conception book with a lot of science in it, I really enjoyed "The Impatient Woman's Guide to Getting Pregnant". All the science is cited and it's an easy read.

I really liked the book "Origins: How the Nine Months Before Birth Shape the Rest of Our Lives". It contained a lot of information a lot of other books didn't and was fun to read.

For a good reference book, I love the 411 series (Expecting 411, Baby 411, Toddler 411). It has really helpful information in an easy to look up format.

I also have enjoyed reading some essays about motherhood including "Waiting for Birdy" about a woman's second pregnancy while raising a toddler, "The Good Mother Myth: Redefining Motherhood to Fit Reality" which is a collection of essays about motherhood, and "Bringing Up Bebe" for a travelogue while parenting.


Keeping calm in new pregnancy after a loss

Sun Dec 14 4:25 AM by ladyhawk in Pregnancy & Parenting

I haven't had to go through anything that is this (I imagine) traumatic. However, I have been pregnant five times, and I do only have two children. During my two successful pregnancies (I miscarried very early in the other three) I pretty much had to just stop reading anything at all, because, for me personally, it wasn't reassuring. It just made it worse. No news, baby books, articles, no online communities, nothing. Just made me more paranoid.

After the 3rd miscarriage, I went to grief counseling, and I continued therapy through my pregnancy with my second child, which seemed to help a lot.

I will tell you, if it gives you any peace of mind whatsoever, that I was told after my second miscarriage, when I was only 20 years old, that I would need a hysterectomy and probably never have children. Five years later, I have all my reproductive organs and have two healthy children.

I know what works for me won't for everyone, but you could maybe try some of these things?


First trimester nausea and keeping it together at work

Sat Dec 13 3:00 PM by aka_laura in Pregnancy & Parenting

Ladies, I am so sorry you're feeling so awful. Do talk to your doctors about this, and expect them to take is seriously. I delayed getting help for way too long because I thought I was just having normal morning sickness and it was NOT normal morning sickness. Once you've tried the usual round of crackers, ginger everything, sea bands, teas, etc. there are prescriptions that can help you stay healthy so you can nurture your growing baby. I had to take enough Zofran and Phenergan to put a horse to sleep and had a healthy, happy baby born to a healthy, happy momma. If things really persist check out http://beyondmorningsickness.com for more options.


The madness of modern parenting

Sat Dec 6 2:27 PM by spacefem in Pregnancy & Parenting

kaybee that is a great write-up, thank you for sharing! do you mind if I split this off to its own topic? because it's worth it!

I especially admired the conclusion:

There is no broad responsibility to create a healthy environment for children (because mothers who were concerned would live in some other environment), and no social imperative to look after children who were born in ill-health or some other misfortune (because mothers who behaved responsibly would have prevented this outcome).


Food restrictions in pregnancy

Wed Dec 3 3:44 AM by aka_laura in Pregnancy & Parenting

Pretty much the only helpful comment I got from a member of the general public while I was pregnant was this super sweet woman at a lecture. We were chatting, I told her I was expecting my first baby, and a few minutes later I mentioned my friends and I had just gone out to a local sushi place. She got this big smile and said "I didn't have sushi until my third kid, GOOD FOR YOU! You'll be a great mom!"

Bless that wonderful woman.


favorite movie about anyone having a baby

Sat Nov 29 4:31 AM by Sonic# in Pregnancy & Parenting

When I was little I was wild about Look Who's Talking. I think the novelty of a narrating baby wore off sometime after I saw Milo and Otis.


pregnancy and anxiety

Sat Dec 13 6:54 PM by Wilde83 in Pregnancy & Parenting

This is my second pregnancy, with unfortunately no children. This statistics page has given me comfort both times even though no one could have predicted the oddball birth defect that ended my last pregnancy in the second trimester. I suppose I was just one of the unlucky 1% last time, and am so hopeful this time. Thank you for posting it!


fired pregnant worker takes it to the supreme court

Thu Dec 11 7:03 PM by jen4knits in Pregnancy & Parenting

The place I work at did the same thing to a temporary type employee when she was pregnant. She had let them know when she was hired that she was pregnant and would be needing a c-secition. But then when the time came she hadn't been at the job for a full year so they said she didn't qualify for FMLA (family medical leave something) and emailed her... (email yes) to say her options were: 1) resign and reapply or 2) call off and get fired after missing work for 4 days.

Needless to say it worries me about my options even though I'm in a different department, with different job type. It will be interesting to see what the ruling is for this and how it affects current policy.


pin it: pocket guide to fish

Sat Dec 6 10:27 AM by spacefem in Pregnancy & Parenting

I have a whole big pregnancy board on pinterest that's kinda fun. There's an infographic version of my due date statistics that a lot of folks have appreciated. So today I added this pocket guide to fish recommendations:

http://www.pinterest.com/pin/135671007500096368/

Totally grabbed from other sources (http://www.fda.gov/Food/FoodborneIllnes ... 393070.htm & http://www.nrdc.org/oceans/seafoodguide/page4.asp) but it mimics a little card that I literally printed out and folded up in my wallet while I was pregnant.


Babyproofing the House

Mon Dec 1 4:16 AM by MFS in Pregnancy & Parenting

We locked down the universe with the first, still pretty tight with the 2nd, but by the time we had #3 and 4, things got a lot looser. We also had so much more stuff that certain areas that were "dangerous" were now totally inaccessible and irrelevant (yay piles of blankies?)


going public with the new pregnancy & parenting forum

Fri Nov 28 7:03 PM by rowan in Pregnancy & Parenting

OMG AKA_LAURA CONGRATULATIONS!