Probability of delivery within x days of a given date

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This graph shows only babies born as a result of spontaneous (non-induced) labor (75% of all participants).

Do babies come on their due dates? Not really. But they seem to come around their due dates. In the survey, only 290 out of 7527 (3.9%) spontaneously arrived on the exact day. But if you look around that date, the numbers get bigger fast... 1820 babies (24.2%) arrived spontaneously between 39 weeks 4 days and 40 weeks 3 days. 3458 (45.9%) arrived spontaneously within a week of their due date. Throwing out inductions makes those percentages even higher: 61% of all non-induced babies arrived within a week of their due date.

I also think this graph is important because it shows how meaningless it is to move a due date one or two days. For example I have a chart comparing first time moms to mothers who've had previous births, and it shows about a 1-2 day difference. But based on this graph, who cares about a day?

What I mean is this: a woman who's not induced has a 61% chance of giving birth within a week of her due date. Let's say we lie to her and tell her a date that's three days early. Now she has a 59.5% chance of delivering within a week of that "wrong" date. It's not really a huge difference.

Data Table

DayIn weeksBabies Spontaneously Born

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

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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.

favorite movie about anyone having a baby

Fri Nov 28 6:44 AM by Meperidine in Pregnancy & Parenting

I think the only one of these I've seen is Juno. It was a good movie but I'm not sure it counts as my favorite if it's the only one I've seen?

zomg, this whole forum is worth it if we get more people exposed to SAVED!

It seems pretty successful already! But still, I agree. That movie was really funny.

My brief opinion on Ferguson and all that

Fri Nov 28 6:11 AM by Storage and Disposal in Random Weirdos

I agree about the body cams.

Yeah, to understand I'd have to live it. I don't want to be in a mindset that causes me to use violence against the person standing next to me when the people causing and allowing the horrible atrocities are out of reach. A big part of me wants to say that I'm incapable of that, but no one can say that with certainty.

Maybe we should bring to light the similar events by starting their own topics here.

Christmas gifts for small children

Fri Nov 28 4:18 AM by aka_laura in Pregnancy & Parenting

My baby needs diapers, since pooping is currently her favorite activity. An 18 month old in no way needs $2000 worth of gifts.

For older kiddos, I kind of like the "something you want, something you need, something to wear and something to read" thing. It's cheesy, but helps focus the holiday a bit.

I also like books, because I feel like someone really can't have too many books. They're easy to store, good for baby brains, and make good donation items if you do end up with a surplus.

how can we spread the word on the touching thing?

Wed Nov 26 8:02 PM by melsbells in Pregnancy & Parenting

I almost never had to deal with this. I was living in a remote area and not interacting much with others. Also, the culture here doesn't seem conducive of interacting with people by touching them.

One of my spouse's young nieces touched my belly and I didn't know how to tell her not to do it. She was immediately corrected by her mother about not touching people without permission.

Then my parents arrived. I mostly just dealt with their touch, but probably not with much class.

Profile updates

Tue Nov 25 4:17 AM by cwbyrvr in Random Weirdos

My occupation used to be "college student/bum" which made it an interesting answer to what I wanted to be when I grew up for sure. Glad to see I wasn't the only one. I changed it, but I already forget what to... probably that I still don't know.

pick an art museum

Fri Nov 28 6:40 AM by Storage and Disposal in Random Weirdos

I often go to art museums whenever I travel. The problem is I hardly ever travel to new places.

One of the more interesting exhibits I've seen was one involving mummies. It might have even been the Nelson-Atkins museum. A lot of museums kind of blur together in my head. I think I had the most fun at the Minneapolis Institute of Art, but that might have been associated with how much fun I had in that city in general.

Babyproofing the House

Fri Nov 28 4:46 AM by monk in Pregnancy & Parenting

So how far do you take the babyproofing experience.

You obviously move hazardous chemical to secured cabinets and put away electric cords that can pull stuff off tables and counters. But what about sharp edges? do you foam rubber the corners of your coffee table? do you put those little covers over every electrical outlet? Do you put a high latch on your doors for when they can reach the knob? Where do you draw the line between protecting your child and this is ridiculous?

Disclaimer, I am not a parent, just a very concerned Uncle who sees parents that are on both ends of the child safety spectrum.

Food restrictions in pregnancy

Thu Nov 27 10:51 PM by rowan in Pregnancy & Parenting

Monterey Bay Aquarium has some seafood recommendations, and they'll have information about mercury.

Herbal teas - what spacefem says about "weird" ones is true. There is one that can cause premature contractions, but it sure as hell isn't mint.

I think the rec was to very strongly avoid St Johns Wort, if I recall correctly. I'll go dig through the info I have from my doctor friends.

dealbreaker opinions

Wed Nov 26 5:29 PM by Storage and Disposal in Random Weirdos

really you guys? I unfriend all the time!

why mute someone? that means they're still going to be seeing your posts, commenting on your photos, getting to be "in" your life, and never know anything changed. what good is happening by keeping them around?

My former art teacher is quite conservative, but I still like his comments on my artwork.

I put people I think are otherwise perfectly delightful on mute because they flood facebook with useless crap. I don't want them to get the idea that I hate them, but I don't feel like seeing pages of what they have to say.

I think a lot of people have opinions I don't care for. Rather than offending someone I know and respect in person, I choose to just not see it. Facebook has a knack for showing sides of people I don't want to see, but it's just small sides of them. To me, it's not worth shutting out the person completely. After awhile, I occasionally take them off mute to see if they stopped with their nonsense.

What's up?

Mon Nov 24 9:26 PM by DWH in Random Weirdos

Yooooooooooooooooo I keep forgetting to tell you I'm in LA until next Saturday and we should grab lunch if you're free!

Wait whaaaaaaaaaat, okay, I'm leaving town tomorrow for Thanksgiving but I'm going to move this discussion to Facebook.

And MFS, of course you should be scared. BAHAHAHAHA

Hello friends!

Fri Nov 28 6:31 AM by Storage and Disposal in Random Weirdos

Welcome back! It's been awhile.

going public with the new pregnancy & parenting forum

Fri Nov 28 4:35 AM by monk in Pregnancy & Parenting

In the process of slowly killing her, according to The Internet.

According to the internet we're all dying, now. In fact I'm typing this post with my cold dead fingers.

It seems to me that the kids today are way more protected than I was as a kid and way way more compared to what my own parents have said about their childhood.


Thu Nov 27 8:11 AM by Mathmo in Random Weirdos

We've been decluttering / organising gradually for months now (and have got rid of lots of things! Lots have been recycled, or cleaned up and donated). I kind of like organising but only when there is enough space to actually put everything in. We've just moved house, so getting the volume of stuff to move down as low as possible for that was a big motivator. I read "The life-changing magic of tidying" by Marie Kondo a couple of months ago and rather liked it. She has a whole philosophy about tidying that I think makes a lot of sense (a practical approach which involves actually handling each item and seeing how you feel about it and saying goodbye gracefully to things).

I find it hardest to get rid of things I no longer want/need but that aren't in great condition - i.e. where I can see that there's still a lot of potential wear in them, but I don't think anyone would buy them from a charity shop. I really don't want to send things to landfill when they could still be used - but I can't keep all of them (current example: slightly stained but otherwise totally functional drawstring cotton laundry bag that I'm not super-fond of and don't need - bought in 2007 when I did need it for Uni ...).

forum suggestion box

Wed Nov 26 2:12 PM by spacefem in Random Weirdos


I fixed the chat pages, sorcery does have a web-based client that's working. next chat day is tuesday!

I forwarded the whole /chat to the wiki so we have one place to edit.

Are you prepared?

Thu Nov 20 12:25 PM by Aelwyn in Random Weirdos

No, not at all. I have nothing stocked in my place.
However I do live less than 2 minutes from a subway which doubles up as a bomb shelter. Handy.