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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
0426739W,5D
1122239W,5D
28939W,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 1 0.1 1 1.1
246 12 0.3 0 0 3 3.4
247 3 0.1 3 0.2 1 1.1
248 13 0.3 3 0.2 1 1.1
249 7 0.2 3 0.2 1 1.1
250 11 0.3 1 0.1 1 1.1
251 8 0.2 3 0.2 1 1.1
252 18 0.4 6 0.5 0 0
253 17 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 2.2
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 2.2
259 27 0.6 12 1 1 1.1
260 30 0.7 6 0.5 1 1.1
261 27 0.6 6 0.5 4 4.5
262 52 1.2 6 0.5 3 3.4
263 49 1.1 14 1.1 1 1.1
264 38 0.9 15 1.2 2 2.2
265 60 1.4 16 1.3 2 2.2
266 59 1.4 19 1.6 2 2.2
267 66 1.5 16 1.3 1 1.1
268 53 1.2 18 1.5 2 2.2
269 86 2 27 2.2 5 5.6
270 106 2.5 30 2.5 1 1.1
271 93 2.2 30 2.5 1 1.1
272 107 2.5 41 3.4 1 1.1
273 129 3 38 3.1 2 2.2
274 129 3 27 2.2 1 1.1
275 126 3 37 3 4 4.5
276 156 3.7 59 4.8 3 3.4
277 171 4 53 4.3 1 1.1
278 181 4.2 51 4.2 1 1.1
279 219 5.1 51 4.2 1 1.1
280 217 5.1 66 5.4 1 1.1
281 232 5.4 51 4.2 1 1.1
282 184 4.3 67 5.5 1 1.1
283 199 4.7 45 3.7 3 3.4
284 183 4.3 37 3 2 2.2
285 180 4.2 47 3.8 1 1.1
286 167 3.9 60 4.9 3 3.4
287 173 4.1 55 4.5 1 1.1
288 122 2.9 30 2.5 1 1.1
289 101 2.4 33 2.7 1 1.1
290 88 2.1 36 2.9 1 1.1
291 87 2 11 0.9 1 1.1
292 50 1.2 25 2 2 2.2
293 53 1.2 7 0.6 1 1.1
294 33 0.8 11 0.9 7 7.9
295 10 0.2 7 0.6 1 1.1
296 15 0.4 4 0.3 2 2.2
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 2 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.

name trends

Mon Jan 26 9:17 AM by Lemon in Pregnancy & Parenting

The popularity of Nevaeh is a sign of the apocalypse. I can't get behind that one. I do love the vintage names coming back though.

Isn't Nevaeh another name for a large freckle? I've also encountered some tragically under-researched names like Candida and Melaena (black faeces). All pregnant women should be issued with a medical dictionary at the booking appointment.


sleep humor

Fri Jan 23 7:13 PM by rowan in Pregnancy & Parenting

Here's a really funny humor bit about sleep, but the same general idea can apply to pretty much any "advice" given to new parents.

"I bought all the top books on baby sleep and development. I read through them all, as well as several blogs and sleep websites. I gathered lots of advice:"

https://chimericalcapuchin.wordpress.co ... babybooks/


Breastfeeding & accoutrements thereof

Mon Jan 19 6:33 AM by Ashenskisla in Pregnancy & Parenting

I have been breastfeeding for the past 10 1/2 years, 1st and 2nd kids until 5 years ish, and currently have a 2 month old. For me it's been very easy.
I think the greatest breastfeeding accessories are the la leche league washable pads, the shape and size makes them invisible under clothes.
http://www.breakoutbras.com/product/La- ... ads-Creams
And bravados body silk bras. Whatever bras you get, make sure they have the easy one hand open and close like these. These bras also come with little matching metal pieces and instructions to turn them into regular bras. Of course with my situation the bras were ready for the trash before I was done using them as nursing bras.
http://www.breakoutbras.com/product/Bra ... rsing-Bras


Why Pocket Diapers Are Better Than Disposables

Sun Jan 11 3:31 PM by Nancy Erick in Pregnancy & Parenting

Hi everyone

A Beautiful article by writer Kathryn McDowell recently I read liked to share with you

Why Pocket Diapers Are Better Than Disposables :


As a young parent, you've no doubt heard of pocket diapers. Perhaps a neighbor or a co-worker told you about them. Or it was your babysitter, who asked you to get them soon. Well, so many families in America are today turning to pocket diapers for their little ones. But a majority still holds on to disposable diapers, while being curious about pocket diapers at the same time.

Why are diapers so great? For a start, pocket diapers come with brand new fabrics and super absorbent pads, are easy to put on, simple to take off, easy to wash and quick to dry. And they are better than disposable diapers.

They are Cheaper
Until your child is potty trained, you'd probably spend something close to $2500 to $3000 on diapers - which is quite a lot. Biodegradable disposable diapers are even costlier. But with pocket ones, you won't have to spend anything more than $350 to $400, till your child is potty trained.


Working as due date approaches

Mon Jan 5 6:18 AM by Bork in Pregnancy & Parenting

However long you end up staying at work, once you're in labor, PLEASE GO HOME. Or to the hospital. Because staying at work while you're in labor is hella awkward for everyone involved.


Because judging other parents is absurd.

Sun Jan 25 6:45 PM by spacefem in Pregnancy & Parenting

Yeah honestly guys, I'm torn on this issue too.

While it's a nice idea to say we should have a sisterhood of motherhood, where do you draw the line? What's crazysauce and obviously wrong to you might easily just be someone else's "personal choice" that they say you have "no right to judge".

So I'd like to reserve my right to judge.

Also, think about this... judging me for being judgy is ALSO kinda judgy, right? It's meta-judgy!

I think women get told too often to play nice. We need to be demure, passive, polite, keep quiet. As a feminist, I want to reserve the right to call people out when I want. I'm not going to go stalk your house or punch you in the face or anything. But I do want to say, "hey... I disagree with your parenting and here's why."

See also... "Stop The Mommy Wars" photos: http://herscoop.com/posts/empowering-photo-series/


It takes 13 million calories to raise a child!

Wed Jan 21 4:32 AM by textualorientation in Pregnancy & Parenting

Recently found out how much energy it takes to raise a child. Woah.

I'm pretty infuriated that in Canada it can cost $1,676/month for daycare, when science actually tells us we evolved to help each other raise children. I wrote a blog about this in case anyone is interested! I would really like to see this change for mothers all over Canada.

https://textualorientation.wordpress.co ... ledaycare/


Work

Thu Jan 15 9:17 PM by bigdaddy in Pregnancy & Parenting

I will do cheers but in people's experiences and options I should be ok


some quotes recently I read

Sat Jan 10 4:50 PM by Nancy Erick in Pregnancy & Parenting

i search about these quotes in google


Bringing home a second child - what do you wish you knew/did?

Fri Jan 2 1:27 PM by spacefem in Pregnancy & Parenting

Good topic.

Ya know, I think the one thing I remember is that it wasn't as big a deal as I thought it was. When I was pregnant I'd look at my three year old and think, "What can we do for this delicate little child whose world is about to be upside-down?" Then the baby came home, the three year old suddenly looked like a teenager to me, and I was like eh go fend for yourself kid. And honestly, she did great. She's still really sweet to her little sister.

Here are some notes:
1) New baby really does deserve some new stuff. I went through the things I'd kept from my first... nasty stained onesies, teethers, pacifiers, "pat the fur" type board books that had more than their fair share of patting (and licking, and yakking on...), I have no idea why I kept some of that. Sentimental value, engineer cheapness? Lots of clothes got reused, sure, but the plain white onesies? Splurge on the poor kiddo and spend $6 on another 4-pack.


34 Weeks

Fri Jan 23 11:57 PM by Sonic# in Pregnancy & Parenting

Probably not. As we pointed out in the other topic, 34 weeks isn't even on the chart because it's so rare:
http://spacefem.com/pregnant/charts/duedate1.php

You'd be better off worrying over a car accident.


Maternity Clothes

Mon Jan 19 4:17 PM by Metcodon1 in Pregnancy & Parenting

As a fat person who is currently pregnant with her second child I will say this. OF COURSE you are allowed to reproduce even if you're chubby. You're allowed to and you can even have a totally healthy pregnancy and a wonderfully healthy child (somehow, despite the fact that my husband and I are both chubby, my daughter is SKINNY - go figure).

I will say this on the topic of maternity clothes though as a fat person. Yes you may be able to wear your regular clothing longer. HOWEVER, maternity clothes make you look pregnant instead of just even fatter. For my own mental health/ego/etc. I really appreciated looking pregnant instead of just fat. Mental health is worth something too.


10 things you can leave off the baby registry

Wed Jan 14 9:38 PM by Zeph in Pregnancy & Parenting

I just plan on asking for different types of cloth diapers, although something tells me that nobody will buy off this registry. :)


Keeping your pre-pregnancy/parenthood identity

Tue Jan 6 4:33 PM by Abc123 in Pregnancy & Parenting

Just wanted to say thanks to all of you!! I have been snooping around on this forum ever since I found out I was pregnant a month ago, and these kinds of conversations have been a huge comfort as I take this exciting, but terrifying, step!


bad language + small children

Wed Dec 31 5:38 PM by octarineoboe in Pregnancy & Parenting

I'm not a parent, but I thought it made a pretty entertaining story when my cousin's almost-three-year-old dropped an f-bomb. Her parents were a little embarrassed but also proud of her for using it correctly. It may help that her dad is a linguist and has a theory that most "swear words" are not truly profane/offensive.