when are babies born relative to their due date?

I'd like to see a graph or some data showing when babies are born relative to the due date that the doctor assigned early on in the pregnancy. Not because I'm worried or anything, I'm just curious about it.

I've read that:
- only 3% of babies are born on their due dates
- first time mums birth later, on average
- caucasians birth later than asians and africans (why??), on average
- up to 10% of babies go as late as 42 weeks (why do they induce then if so many babies are naturally that late how is that a problem?)

I'd like to learn more about it. Does anyone know a source of more detailed statistics?

One thing I'm really curious about is whether the due date falls on average mid-way in the spectrum. If the due date calculations are accurate, you'd expect half of babies to be born before it and half to be born after it. Is that actually right?

Anyone know more about this?

I don't know about accuracy but my DD (who is my first) came 4 days early.

I am a first time mum and my ds was born 40+7 (7days late). Was due to be induced at 41+4wks.

I read in a book recently that the average of pregnancy is 41 weeks and 1 day.

My DD was 11 days late. I was due to be induced at 10 days over but chickened out, went into labour and she was born at 11 days o/d. Labour was augmented, without augmentation she probably would have been born at 12 days over.
It would be interesting to see how many are born before vs after their EDD. I wouldn't think it would be 50/50 though because there is a much longer time in which a baby can be born prematurely (15 weeks or more) as opposed to overdue (eg you never hear of a baby going 15 weeks past their DD).
I think the reason for induction for post dates is that there are some studies that show an increased rate of neonatal death at 41+ weeks of pregnancy.

My Bubba was due on the 21st October but came on the 28th October, we were due to be induced the day she arrived, so thank goodness for that!

Both my girls were born on their EDD!!! and both were the 9th of the month

In saying this I received 2 edds for both girls due to having numerous early scans. I was charting for both pregnancies and was given the 9th as a due date based on my ovulation. Then at both my first early scans the edd was the 9th for both girls so I stuck with this edd. I really hope all that made sense.

HI
Number 1 was 14 days early. No 2 was 10 days early. Number 3 has 10 days to go.All girls.
L.B.

I would be very interested to learn these stats too so will be watching this thread closely. To add to Tenar's questions, I would also like to know: Do some women have naturally shorter pregnancies than others, i.e. is the standard 40 week pregnancy an average and do some women naturally give birth at say 38 weeks, while others naturally wait til 41 weeks, etc? (hope that makes sense.)

My DD was born 4 1/2 weeks early, completely healthy, able to breathe, feed, etc, no need for NICU. Many babies in my family have been born early (e.g. I was about 8 days early, my brother was 10 days early, neither had any complications), so I am wondering if it is normal for some babies to come earlier than others.

Thanks for the replies so far. I'm still hoping that someone will have some statistics on this.

thepixie, that's a good point that there are more weeks available to be born early than late. Hmm, if the due date is the "average" day a baby will be born on, it depends what kind of average.

If it's the median date, then by definition, 50% of babies would be born before then and 50% after then.

But if it's the mean date, then the early babies, since they can be earlier than the late babies, would pull the average earlier, so the due date would be actually a bit early, which seems to be common.

I was also wondering later on, what is it that makes a baby be born? There must be some kind of hormonal trigger in the baby or both that says "I'm ready to come out, let's do this birth thing", or in the Mum that says "I've had enough of carrying you around inside". Do we know what that is and how it works?

Im not sure why.
The figures I read were 5% on EDD, and yeh, first time mums in general, go over their EDD.

38-42 weeks is full term, so a baby isnt "late" til 42 weeks is reached.

I think one of the main reasons would be that not everyone has a 28 day cycle, ovulates on day 14 etc. Drs dates often take this as the basis for their calculations.

Maybe you could ask the Mods if you (or they) could create a Poll that way you can collect stats from the women on here??

Unless there is something somewhere else of course :redface:

NaeNae - the "Who's due" thread has a section at the start with figures form births reported on BB, for gender, c/s-vb, and early, EDD or post EDD births :)

Its one of those things that there will never be a quantative answer for. I know you have a scientific background, but not everything can be answered scientifically kwim? There are several thoughts about this, somewhat like the 'chicken or the egg' question. Some say that the baby instigates the labour and others say the mother, and some say both together. It's true that even if a baby is ready that the mother can delay the process by not letting go emotionally - many women who've gone past dates go into labour on their own once an induction or c/s date has been booked - almost signalling that it's *safe* to give birth. I personally believe that our mind plays a huge role and we have to stop thinking with our 'concious' brain when it comes to birth and think with our 'primative' one (there is something on here about it that Kelly posted some time ago).

The giving of an EDD is just that - an ESTIMATED date that baby should arrive, but it is accepted that term is anything from 37 to 42 weeks (some women even go to 44) so as long as your baby is born within that time frame then there is no cause for concern really, baby will come when it's time to come. And even then the giving of an EDD would only be a recent thing that I would assume would coincide with when birth became medicalised and hospitals and Drs had to be booked ;) . Decades ago a woman didn't even acknowledge the pg till she had felt the 'quickening' (first movements) and only worked on a rough guide for when the babe should be born. Many factors can alter your EDD too - length of cycles, day of ovulation and then implantation. Some babies need to gestate for longer to be fully developed and others need a shorter time. There's really no science to it, its just one of those things that is completely beyond prediction.

i was given so many due dates for my daughter - two by my last period (one Chinese dr and one Caucasian); 3 different dates by scans and she was born on a different date to all of them. The first date I was given was September 1st and by my first scan at 8 weeks the date was September 19th (other dates were 3rd, 10th, 14th), the first scan is supposed to be the most accurate date but she was born September 7th (went into labour 12:30am on the 6th and she was born just over 38 hours later). The last scan I had at 35 weeks said that she was going to be born the 10th. The only regular periods I have had in my life were 2-3 cycles before she was born that seemed to have some kind of pattern so maybe this was of influence??

I love statistics! and I too was curious about this. this is the best I could do with 10 mins of surfing:

http://en.wikipedia.org/wiki/Pregnancy#Duration

^ Dr Sally Tracy, Having a Great Birth in Australia ed. David Vernon, Australian College of Midwives, 2005, p22

Fewer than 5% of births occur on the due date; 50% of births are within a week of the due date, and almost 90% within two weeks.[16] It is much more useful to consider therefore a range of due dates, rather than one specific day, with some online due date calculators providing this information.

I think with some more surfing and changing search terms etc one could find the answer to this. Some of this scientific stuff can't even really be found on the internet, it's in jouranls and whatnot, so if you're really keen on it you can look in a book or a journal at the library or university library near you.

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the mother can delay the process by not letting go emotionally - many women who've gone past dates go into labour on their own once an induction or c/s date has been booked - almost signalling that it's *safe* to give birth.

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I firmly believe this after DD - I was due on the 30th and because DS was 6 days late I told my Mum not to bother coming down to Melbourne till the 29th. She was very nervous about this and I was fine, the OB said that if it took my body that little bit longer to "bake the baby" LOL that was probably the way I would go again. Every woman is different and some have longer pregnancies than others and different labours etc etc.

Anyway, I went into labour the day Mum was due to come down, and I truly believe it was because I knew she was coming so DS was going to be looked after so it was "safe" to give birth. And I know the first time around I was quite apprehensive and not looking forward to labour at all and the day I did go into labour it was Saturday and DH was home. I wasn't by myself therefore it was "safe".

In terms of stats and graphs, my OB said that 5% of babies come on their due date so that means that 47.5% come between 38 and 40 weeks and the other 47.5% come between 40 and 42 weeks and there would be a peak around the 40th week, giving or taking a few days because the average pregnancy is about 40 weeks, hence the EDD they give you.

As for what triggers labour, I have read they still don't know.

DS was 2 days late, DD was 3 days late.