Due date - what is the best way to calculate

[Em1984]

I've been looking around to see the best way to work out due date, apart from ultrasound, of course. Seems highly variable. THoughts ?

I always thought your dd was worked out from the first day of your last period.

I think the date calculated from the size at the 12-week scan is supposed to be the most accurate, as up to that point babies all grow at about the same rate - after that there's a lot more variation.

Calculating from your last period depends on having regular periods - if we went by mine I should be giving birth last week! (I'm at week 30).

Although our NCT tutor is at great pains to emphasise that there is a 5-week window during which babies are considered bang on time, and we ought to completely ignore our 'due dates' from now onwards!

The window is massive on the variable due date, I used due date calculators and went with my twelve week scan but was never told this, I found it out on the red baby book (www.redbabybook.com I think) where they show the chances of giving birth on your due date and its only something like 5%!!!!!

They also show all the chances of giving birth for about 2 weeks before and after.
Plus they have a pretty good due date calculator, which takes loads more stuff than anything else I have seen on the web and they give you loads of information about your date, like star signs without the need to sign up to anything or lots of annoying ads all over the place

I agree that 12 week scan is best predictor, but it should be useful to have a 'traditionally' predicted date, as if there is a discrepancy between the two it could be because the baby is not growing normally. Baby is then smaller, less developed, and the ultrasound will wrongly think it is younger. I don't want to worry unnecessarily if there is a big discrepancy so I want the most scientific way possible. Thanks for the www.redbabybook.com link. Methods look fancy. Let's see how it compares when I get scanned !

LOL Em

I am really grateful for the www.redbabybook.com link. It is the best due date calculator I've found. Loved it. Thanks.

12 week scan confirms(ish) the previous calendar/lmp dategiven only 4% of babies are born on due date... i am now thinking of things in terms of a window....eg any time between 37 and 42 weeks...

I found that site didn't work - it kept thinking my due date was my LMP date and when I put my LMP date in it gave me a due date 11 days later than it actually is!

The problem with all of these calculators is that they assume a regular cycle, which I didn't have for a few months before I got pregnant. Hence I am waiting for a dating scan to give me a more accurate date. I do know the ovulation date but I can't find a way of calculating a due date from that. Even my midwife didn't know.

tbh, i know what date the dirty deed was done and would have thought this would give a fairly accurate due date +/- a few days but can find anything which would use this.

cathym , if you know the ovulation date, just count 14 back from that and put that date in to one of the 'traditional' LMP calculators. I have PCOS and the same problem, my cycles were weird, luteal phase too short, etc., so that's the way I calculated it. My GP agreed with my method when I told her. Traditional LMP calculators assume you ovulate on day 14 of a 28 day cycle, and the ovulation day is really the only day that matters (not the day you BD). Really surprised your at midwife not knowing this!

Wombleprincess
www.amazingpregnancy.com/timeline/ allows you to put in conception date

My midwife did it by using my LMP, adding a week then counting 9 months from then. I was quite impressed with it as She came up with the date i'd been given on 2 scans and the one all the online calculators had given me.

My midwife did it by using my LMP, adding a week then counting 9 months from then. I was quite impressed with it as She came up with the date i'd been given on 2 scans and the one all the online calculators had given me.

www.amazingpregnancy.com/timeline/

They are really useless though to be honest. My ultrasound scan dates are wrong (I had fertility treatment, so I could tell you to the hour when I conceived ), and a term baby is anything from 37 to 42 weeks anyway... I drove myself nuts with EDDs last time around, and everyone else drove me even more nuts. I have been much more cagey with the EDD this time around. I'll let you know if it stops the "have you had it yet?" phone calls from irritating relatives when I hit 8 months-ish.