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 306 out of 7659 (4%) spontaneously arrived on the exact day. But if you look around that date, the numbers get bigger fast... 1864 babies (24.3%) arrived spontaneously between 39 weeks 4 days and 40 weeks 3 days. 3529 (46.1%) arrived spontaneously within a week of their due date. Throwing out inductions makes those percentages even higher: 61.1% 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 61.1% 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 59.6% 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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How is pregnancy different from when it's shown in TV?

Wed Dec 17 10:48 PM by C˙glas in Pregnancy & Parenting

I have been binging on Call the Midwife. While they show a lot of the realistic ugly side of labor (although with quantitatively less fluids and blood, I'm sure), one thing that I find missing from this show and many others is weight gain on a pregnant woman other than in her belly. Perhaps the calorie intake in 1950s East End London was small enough to warrant a distinct lack of arm-chub and second chins, so I'll give it a pass, but I almost never see it elsewhere. I was surprised to see in How I Met Your Mother that not only did the petite Lily gain a second chin with her pregnancy, but it didn't immediately disappear after birth, either! I find myself surprised, when friends and family become pregnant, at how puffy their face gets and how the rest of the body grows, even if they gain a safe amount of weight, because of course on the screen the svelte actresses just get a belly harness.

You aren't instantly big and pregnant the day after you pass the test, in fact you might not feel pregnant at all.My goodness, yes. I didn't really believe I was pregnant until after an ultrasound, and even then I kept a suspicion that there was some kind of sonogram mix-up going on. I only had a bit of nausea which wasn't out of line with GI troubles before, so none of that Hollywood quick-and-easy vomit-once "oh! I'm pregnant!" stuff. I actually found the increased sense of smell a lot more tangible of a symptom, but I suppose that's not as easy to play on screen.

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 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:

Totally grabbed from other sources ( ... 393070.htm & 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