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 12 0.2 4 0.2 1 1.1
246 15 0.2 1 0.1 3 3.2
247 7 0.1 3 0.2 1 1.1
248 17 0.3 3 0.2 1 1.1
249 16 0.2 4 0.2 2 2.1
250 15 0.2 5 0.3 2 2.1
251 16 0.2 3 0.2 2 2.1
252 27 0.4 8 0.4 1 1.1
253 23 0.3 3 0.2 0 0
254 19 0.3 11 0.6 1 1.1
255 30 0.4 7 0.4 1 1.1
256 18 0.3 9 0.5 2 2.1
257 21 0.3 12 0.6 1 1.1
258 31 0.5 9 0.5 1 1.1
259 53 0.8 17 0.9 2 2.1
260 42 0.6 13 0.7 1 1.1
261 45 0.7 13 0.7 4 4.2
262 67 1 11 0.6 4 4.2
263 71 1 20 1.1 3 3.2
264 59 0.9 20 1.1 3 3.2
265 89 1.3 24 1.3 3 3.2
266 98 1.4 31 1.7 1 1.1
267 91 1.3 26 1.4 1 1.1
268 96 1.4 27 1.5 2 2.1
269 133 2 40 2.2 1 1.1
270 161 2.4 45 2.4 1 1.1
271 142 2.1 41 2.2 1 1.1
272 164 2.4 60 3.2 1 1.1
273 216 3.2 62 3.3 3 3.2
274 195 2.9 46 2.5 1 1.1
275 205 3 55 3 5 5.3
276 252 3.7 86 4.6 5 5.3
277 276 4.1 75 4 1 1.1
278 284 4.2 72 3.9 1 1.1
279 321 4.7 85 4.6 1 1.1
280 392 5.8 106 5.7 1 1.1
281 381 5.6 85 4.6 1 1.1
282 293 4.3 98 5.3 1 1.1
283 305 4.5 70 3.8 1 1.1
284 286 4.2 64 3.4 2 2.1
285 281 4.1 67 3.6 1 1.1
286 274 4 88 4.7 1 1.1
287 280 4.1 70 3.8 1 1.1
288 220 3.2 45 2.4 2 2.1
289 165 2.4 50 2.7 1 1.1
290 150 2.2 54 2.9 1 1.1
291 129 1.9 16 0.9 2 2.1
292 78 1.2 36 1.9 3 3.2
293 79 1.2 14 0.8 2 2.1
294 52 0.8 15 0.8 1 1.1
295 15 0.2 12 0.6 1 1.1
296 20 0.3 6 0.3 2 2.1
297 15 0.2 5 0.3 2 2.1
298 8 0.1 3 0.2 1 1.1
299 7 0.1 1 0.1 2 2.1
300 7 0.1 1 0.1 2 2.1

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

Recent Comments

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you are invited to join our pregnancy forum. We are dedicated to answering complicated questions as logically as we possibly can.

To all Moms: Where do you go for financial concerns?

Tue May 9 4:18 PM by rowan in Pregnancy & Parenting

My father in law does financial advising so we kind of have an in-house advisor? But seriously someone with expertise is great. There are various "how to do finances" through our local community ed, which I'd probably consider if I didn't already have someone to ask. Maybe something like that near you? Libraries also sometimes have programs.

Also I know you can do wills and stuff on your own but honestly I found it super useful to talk through it with a lawyer who does that. She thought of things we never would have. (hm really should revisit now that kid is older) It was a one time fee and not that bad.

We do most of our banking through a credit union. Have been happy with them. We refinanced our mortgage through them when we did that. I remember the big credit union bust ages ago, but there are lots more protections in place now and big banks can be pretty awful.

stuffed animals

Thu Feb 23 1:20 AM by antfancier in Pregnancy & Parenting

My brother's favorite stuffed animal was a thing we called 'gerbil'. I actually don't know what it was because we found it in the street (not sure what my mum was thinking in allowing him to pick it up, let alone keep it) and it had already lost an eye and was unidentifiable, but he became really attached to it. We almost missed a flight once because he dropped it in the airport and we had to go back to look for it.

Today for the first time my 11month old showed interest in a stuffed animal. Just before Christmas we received a box from Amazon with a giant bear inside. No gift wrap, no note. Just a bear the size of my child. It's been sat in his room and ignored completely, despite him exploring literally everything else that is in there. Then, out of the blue, he made a beeline for it and tried to pull its eyes out.

tactile stuff

Wed Jan 4 6:14 AM by Neko in Pregnancy & Parenting

All the pliable/crafty stuff I can think of has been mentioned. ETA: I lied. Bread dough!

But if generally tactile surfaces also apply, mermaid sequin pillows are comforting. It was one of my impulse buys at a department store about a month ago. I couldn't stop petting the display. The sequined side seemed like it wouldn't be comfortable to rest on but it hasn't been an issue. My stepdad really likes them so I got him one for giftmas and he said it helps distract him when chronic pain keeps him awake at night. https://www.etsy.com/listing/470423508/ ... _active_40

I haven't field tested them on my nieces and nephews yet. That could be fun.

protective restrictions for children

Tue Dec 6 10:08 PM by melsbells in Pregnancy & Parenting

The Wolfpack, a documentary about six bright teenage brothers have spent their entire lives locked away from society in a manhattan housing project. all they know of the outside is gleaned from the movies they watch obsessively (and recreate meticulously). yet as adolescence looms, they dream of escape, ever more urgently, into the beckoning world. The film is coming from the bias that the parents have wronged their children. We're told that in the past they have left the apartment, only as a group, and up to eight times a year. One year they didn't get out at all. It's unclear what the objective of these outings were. The film leaves a lot unanswered. We know they are homeschooled by their mother, who's a certified teacher, but what the homeschooling looked like is never examined. I can't help but think that these kids all around really healthy, charming, affectionate, considerate, welcoming, really only positive adjectives come to mind.

Sleep Training for Parents and Infants

Sat Oct 1 9:34 PM by antfancier in Pregnancy & Parenting

Thank you! I'm currently stuck under 20lbs of sleeping baby because all day time naps have to be in my arms or they don't happen.

Bilingual Toddler

Wed May 3 10:19 PM by Nachos in Pregnancy & Parenting

Bilingualism! This is something I know a lot about! My last job was to speak English to my class in a partial immersion school and the kids picked up English so fast but spoke back to me in German. We worked on saying different words in German and in English and it meaning the same thing and I read English books to them. They differentiated pretty well but most of them came from a mono-lingual family background.

I can still highly recommend this book: (https://www.amazon.com/Third-Culture-Ki ... 1857885252) for bilingual children. Some very good advice in there.

Also, keep speaking English! Toddlers forget fast when a language is no longer present.

Yay bilingualism!

New parent help/suggestions

Sat Jan 14 10:07 PM by antfancier in Pregnancy & Parenting

I agree with everything lyra211 said and will add a few more.

Things you don't need:
Anything soft, fluffy or furry. My baby couldn't care less about minky blankets and soft toys. Plus they seem more gross to clean when they get covered in bodily fluids.
Clothes that look like adult clothes. It's so difficult to squeeze baby thighs into miniature corduroys or denim jeans which have no give to the fabric.
Baby washcloths. Babies make a disproportionate amount of mess so you need adult size washcloths to clean them up.

Things that were super useful:
A folding changing mat. I have a SkipHop one which has enough storage for wipes and diapers, which was all I needed to carry with me when I had a newborn. Now that he's bigger, I appreciate the larger size of the mat because the one that came with my diaper bag is way too small.
Balls. They were the first thing he played with and still his favourite toys. At the beginning he liked one made by Oball which was easy to pick up, and a soft fabric one which made a crinkly noise. Now he loves throwing a soft rubber ball and watching it bounce.

development balalnce

Fri Dec 16 5:02 PM by rinn in Pregnancy & Parenting

I was proficient in fine/gross motor skills and cognitive development for my age, but I was further behind in speech/language development and social/emotional development. I caught up in them perhaps by ages 5-7, with vestiges of social issues lasting longer (like my temper). There was nothing inherently bad about being a bit off in timing, though in my case my imbalance was severe enough that I did need professional help from a speech pathologist.

....New social situations make me feel somewhat awkward, but I've also learned that many other people feel the same way about novel contexts, so I think I'm with the curve there.

geez, are you my twin, sonic? XD

I grew up with definite lag in speech/language development. I had a speech pathologist in elementary school work on my -L-'s, -r-'s and -th-'s; and when I essentially "graduated" from it I was taken out of the IEP program. my mom and I now see that being a mistake. middle school went decently, but I struggled in language arts; and by the time I went into high school I was struggling in my history/English humanities course and Algebra. I struggled in English classes because of my inability to express myself through language clearly, and I struggled in algebra because I couldn't follow a thing my teacher was saying (we had someone tutor me who literally asked why she was tutoring me because I grasped the concepts five minutes after her explaining it).

Parents Warned they Could Lose Custody of Fourteen-Year-Old Over This

Mon Nov 7 3:33 AM by garbage videos in Pregnancy & Parenting

It is wrong to lock horses in cages and breed them as if they are slaves.
I sincerely hope that you aren't condoning slavery with that implication that it isn't wrong to keep humans in cages and force them to "breed". It's probably just an unfortunate word choice.
I said it is wrong to put horses in cages and breed them as slaves. So I don't know how you read things. Frankly you are irritating me because I shouldn't have to explain how I said 2+2=4 when you are accusing me of saying 2+2=5. In this age people should have mastered how to read clearly and I shouldn't have to micromanage my text and clear what I have already layed out clearly for you.

To be fair, if the girl is a Female to Male transsexual, her hormones are not so important, at an old age Male hormones will mutate her body and have the same effect. But with boy's its more tragic and serious. Boys who want to be girls, must stop their toxic T at an early age, or else their face will be permanently ugly and bony

bringing children up naturist

Sat Sep 24 1:18 AM by filmmakingally in Pregnancy & Parenting

It's about teaching children to make love so that they do it themselves. Love has no age or genetic requirement. It's healthy for young siblings to make love, and it's unhealthy if they don't. Sexual repression of children fucks them up as adults. Because the parents are secretive about it, children get the idea that it's bad, which starts the process of sexual repression.

Gross. Yuck. Eww. I've run out of ways to express how disgusted I am with what you've said here. Ewwwwwww!!!!!!!

No, siblings should not make love. It is in our genetic interest that we don't do this. Ever. This is a cultural universal.

What did I just say?

Wed Mar 15 12:25 PM by mariareese in Pregnancy & Parenting

Looking to know about the system and biology :D hehe ..

Activities for 1-3 yo's

Sat Jan 14 7:07 PM by antfancier in Pregnancy & Parenting

I find theimaginationtree.com has lots of inspiring ideas. Some look like they take quite a bit of prep, but if you're doing it for a whole class then it might be worth it. You can sort activities by age as well so it's easier to search.

Academic redshirting

Wed Dec 7 8:22 PM by Nachos in Pregnancy & Parenting

I'm on the fence about this. I was always the youngest in my class because I was born 2 days before the cut off. I started school JUST after my 5th birthday (Go England.... not...) and this made a huge gap between me and the oldest kids in the class who were almost a whole year older. However, even though I might have struggled more then I'm ok now, you know? It might have even been helpful for me, pushing myself to learn more and try and be smarter. My sister was held back for a year in preschool in Germany because she didn't speak German well enough for the first grade and so she has always been the oldest in class and she's not really as academic as me. This is all anecdata of course, but interesting to ponder over.

kids' obsessions

Sat Oct 15 8:08 PM by melsbells in Pregnancy & Parenting

I could see saunas becoming an obsession for a number of very social reasons as well, depending on your family's sauna practices. I honestly can't think of any common themes or rituals shared by all branches of my U.S. family, other than like eating together, but that seems too banal(/essential for survival) to really become an obsession. My Finnish family, on the other hand, all sauna as a social ritual. Whether or not you allow your kid in saunas yet, if there's a lot of exposure to the ritual, they could probably pick up on the social importance. It might make sense that kids are probably wired to pick up on things that the adults in their life think are important (**not a child psychologist**).
<...> I know I was super into the instant evaporation of water and associated *hissssss* the first time I was in a sauna at like age seven.
This is an excellent point. And although I know they exist, I haven't encountered any Finns who don't like sauna. There are a lot of steps to it. The kid gets to help their grandfather build the fire when we're together, knows that wood burning saunas are better than electric saunas, and absolutely loves the sound of the water hitting the hot stones. I can't imitate the sound as well as the kid does.

Don't give your kids antidepressants.

Thu Sep 15 9:13 PM by Nachos in Pregnancy & Parenting

Mental health issues will never start to hurt, therefore no preemptive treatment is needed.

Mental health issues hurt, take it from me. There are many psychosomatic disorders out there which affect your body even though the real problem is in your mind. But to get better, you HAVE to treat both. Pre-emptive treatment also can stop some disorders from becoming too bad. And yes, sometimes drugs can be very very helpful.

I don't think you know what you're talking about and all this "I know because of divine intuition" bullshit is starting to piss me off. if you ask others for sources, be kind enough to provide some yourself.

If this thread continues to be shit-slinging, I will lock it.