spacefem.com

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
0482239W,5D
1135039W,5D
29639W,0D

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 3.1
247 3 0.1 3 0.2 1 1
248 13 0.3 3 0.2 1 1
249 11 0.2 3 0.2 1 1
250 14 0.3 2 0.1 1 1
251 10 0.2 3 0.2 2 2.1
252 19 0.4 6 0.4 0 0
253 17 0.4 2 0.1 0 0
254 14 0.3 9 0.7 1 1
255 29 0.6 4 0.3 1 1
256 15 0.3 9 0.7 1 1
257 14 0.3 11 0.8 1 1
258 23 0.5 3 0.2 2 2.1
259 33 0.7 12 0.9 2 2.1
260 35 0.7 6 0.4 1 1
261 30 0.6 8 0.6 4 4.2
262 58 1.2 8 0.6 3 3.1
263 53 1.1 17 1.3 3 3.1
264 41 0.9 16 1.2 2 2.1
265 65 1.3 19 1.4 2 2.1
266 68 1.4 24 1.8 2 2.1
267 72 1.5 19 1.4 1 1
268 63 1.3 18 1.3 2 2.1
269 98 2 28 2.1 5 5.2
270 120 2.5 31 2.3 1 1
271 102 2.1 31 2.3 1 1
272 122 2.5 50 3.7 1 1
273 146 3 42 3.1 2 2.1
274 143 3 30 2.2 1 1
275 147 3 43 3.2 4 4.2
276 171 3.5 61 4.5 4 4.2
277 195 4 60 4.4 1 1
278 204 4.2 52 3.9 1 1
279 240 5 59 4.4 1 1
280 245 5.1 70 5.2 1 1
281 259 5.4 57 4.2 1 1
282 205 4.3 74 5.5 1 1
283 219 4.5 50 3.7 5 5.2
284 206 4.3 44 3.3 2 2.1
285 205 4.3 52 3.9 1 1
286 194 4 66 4.9 4 4.2
287 198 4.1 58 4.3 1 1
288 144 3 32 2.4 1 1
289 116 2.4 35 2.6 1 1
290 108 2.2 40 3 1 1
291 103 2.1 13 1 1 1
292 57 1.2 26 1.9 2 2.1
293 55 1.1 10 0.7 1 1
294 41 0.9 11 0.8 7 7.3
295 13 0.3 7 0.5 1 1
296 15 0.3 5 0.4 2 2.1
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 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
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.

What new thing did your baby do this week?

Fri Jul 31 3:04 AM by DarkOne in Pregnancy & Parenting

My just-turned-2 yr old started answering yes/no questions with a most casual1-shoulder shrug and a "Sure..."

- Do you want more milk?
- (half shrug) Sure...
- o_O


RIE parenting

Thu Jul 30 2:37 AM by rosefox in Pregnancy & Parenting

No good-sport-ness needed at all! This is exactly the sort of advice I was hoping for.

I linked to the RIE educator blogs because some of the specific things they've discussed have really hit home for me--the difference between comforting a crying baby and trying to shut them up, for example, or the need to sit on one's hands (I have a terrible problem with doing-for around other adults, never mind kids!), or the videos of actual adults and kids interacting. I definitely find that more (potentially) useful than the more general philosophical/marketing stuff.


for all you moms and future moms

Tue Jul 21 2:28 AM by DarkOne in Pregnancy & Parenting

Eek and here I was about to say this felt like a tame version of Mother Lover.


if you need to breastfeed, please cover yourself

Mon Jul 13 12:32 PM by DarkOne in Pregnancy & Parenting

Sorry to CPR a dying thread, but I came across this, and thought I'd share.

LURZqBig734


Antidepressants during pregnancy

Thu Jun 25 1:03 AM by Aum in Pregnancy & Parenting

http://www.henriettes-herb.com/blog/pos ... ssion.html

Pre and post-partum depression have similar reasons, physically speaking. Check nutrition first.


Newborns are difficult!

Thu Jul 30 8:13 PM by Bork in Pregnancy & Parenting

Already two months old???? When did that happen?? His little outfit is so precious!

Super glad to hear that you're feeling better.


Braxton Hicks questions

Mon Jul 27 2:13 PM by Metcodon1 in Pregnancy & Parenting

In my experience "real" contractions are pretty much the whole uterus (top, bottom and lower back). I remember reading somewhere that the ones that get you dilated from 0-7/8 cm are largely the muscles pulling up, trying to stretch the cervix out. As a result many people largely do feel them most strongly at the top of their belly. Whether you feel them strongly in your back or not depends on how the baby is positioned. If you've heard the term "back labor" that usually happens if the back of the baby's head is pressed up against your spine (less common than when the baby's face is on the spine). The contractions that take you from 7 or 8 cm to 10 - i.e. the ones in the part of labor known as "transition" - do tend to be lower down (and also more painful). That said, I think there is A LOT of variation in experience...


the wonder weeks: practical help for parents or self-fulfilling quackery?

Mon Jul 20 2:29 AM by geerlady in Pregnancy & Parenting

I am actually a big fan of the wonder weeks. I found it better than most popular level books looking at infant development. My son was right on the clock for the fussy/happy times, and it was interesting to look for the new skills that I might not have noticed if I hadn't been watching for them.

On the other hand, I stumbled upon this accidentally, so didn't have any hype surrounding it. I also read the author biographies before picking up the book, so took everything with a grain of salt knowing that 1) the authors specialized in chimpanzees, not humans, and developed their theories based on chimps; 2) the bulk of the research is greater than 20 years old and so much of the book is out-dated; and 3) given #'s 1&2, incidental parenting advice had to be filtered.

That said, I still found the book useful and regularly recommend it to people.


Spacefem's homemade playdoh recipe

Mon Jul 13 3:01 AM by Zeph in Pregnancy & Parenting

A parent in my Kindergarten class would bring us homemade purple play dough that smelled like grape!


cosleeping

Fri Jun 12 4:01 PM by spacefem in Pregnancy & Parenting

Thanks! I was going to put my labor story in Random but never got around to it. I can try to do it soon - it's written out already so just a matter of editing.

Yes you must! I'm happy to hear from you, hope everything went and is going well :)


teething necklaces

Thu Jul 30 11:41 AM by DarkOne in Pregnancy & Parenting

A few of the more enterprising/crafty moms in my old parent group got together with a group of friends and bought beads in bulk from alibaba or some other site like that. Some sold the necklaces locally, some made really affordable gifts for friends; I almost jumped in, because a couple of years ago these were still hovering at the $30 mark, but at ~$15, they're much more affordable now, methinks.

They babies I witnessed munching on these were really going to town on them, too.


do you have a parenting goal?

Sun Jul 26 5:16 PM by rosefox in Pregnancy & Parenting

I'm definitely in the "happy healthy child is my only goal" camp. I know some people who are superstars in their chosen fields. From what I can tell, being a superstar is completely exhausting and often really psychologically taxing. So if my kid isn't naturally inclined that way, I certainly don't intend to push them.

If I'm hoping for anything, I hope they'll end up being a quirky artsy/techy type like just about everyone else in the family. But my brother's a corporate lawyer and I love him anyway, so even if our kid turns out to be a white sheep, they'll just bond with Uncle A and it'll all be fine. :)


Diaper bags

Wed Jul 15 3:46 AM by geerlady in Pregnancy & Parenting

We used/still use our diaper bag quite a lot.

For our little guy's first year of life we were urban dwellers and I would often go out for half a day at a time. I would take a diaper for every hour I planned to be out of the house plus one, which was too much for the clutch. I needed a change pad, since he was often changed in nasty places, wipes, hand sanitizer (for changes away from running water), Kleenex, and disposal bags. He needed spare clothes, I needed a spare shirt (discovered after an emergency, useful many times afterwards), and it was useful to have a plastic bag for clothes which were victims of a diaper explosion. For longer days out I would bring two spares for him (and did have days where I used both). I would also have a nursing cover and a blanket in there. We also had a stroller cover for napping which was quite handy when we were taking the stroller as opposed to a carrier. And then there was my stuff, like my wallet, phone, lip balm, keys, granola bar, etc... I did pack the camera, and was often glad for it. Nearly all of our first year pics were from our little excursions.


Pregnancy insomnia

Thu Jun 25 9:05 AM by Gnarlbanya in Pregnancy & Parenting

Thanks for the tips. It's not so much getting to sleep that's the problem, it's staying that way that is causing the issue - too many things waking me up. I seem to be in a bit of a pattern now of alternating good and bad nights, which I guess I can live with. Meanwhile, Netflix is getting a damn good workout in the early hours.


Flying during third trimester

Wed May 27 2:03 AM by ablotial in Pregnancy & Parenting

Thanks, I love the part about not being able to lower the tray table all the way :) I never would have thought of that.

Normally, my doctor said not to do aspirin or ibuprofen for pain relief, but only tylenol (acetemenophen) and even that only if -absolutely- needed after trying other remedies (like heat pack, cold pack, resting with lights closed eyes shut, etc). But the directions for flying specifically say to take one baby aspirin (81mg) a day for three days before the flight as well as the day of the flight to prevent blood clots. My guess is the risk of such a small dose is outweighed by the benefit of not getting blood clots for this particular situation.