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can dating scan dates every be really wrong??

(7 Posts)
sunface Tue 19-Jul-11 13:33:51

i'm 29 weeks this week with my 3rd, but bump is measuring 3cms ahead of where it should be, putting me at 32weeks?! Midwife not remotely concerned, but i have managed to convince myself that i'll now be 2 or 3 weeks before my due date that was given at my scan.

I only had a day long period way back in December but they have worked out my due date in the usual way, using the last day of my period. i'm now thinking what if i was actually pregnant at that point?? sorry, know i am rambling but my next appointment isn't for another 6 weeks and can't think of anyone else to ask! Thanks ladies!

ShowOfHands Tue 19-Jul-11 13:38:19

Did you have a dating scan at around 12 weeks? They are accurate to within about 5 days as in the first trimester babies grow fairly uniformly and by 12 weeks or so are easier to measure than in previous weeks. They should have looked at your lmp date and compared and if there was more than a week's difference they would have changed your due date to tally with the results of the scan. So yes, they're fairly accurate. Dating from LMP however, is not.

It's actually ok to measure a couple of weeks ahead or behind owing to genetic factors and the inaccuracy of measuring the fundal height in the first place.

And none of this changes the fact that the baby will come whenever it's ready anyway. Usually somewhere between 37 and 42 weeks which is the normal gestation period for a baby.

KnitterNotTwitter Tue 19-Jul-11 13:41:26

Bump size isn't the same as baby size... and the fundal height measurement is just a rule of thumb thing, not science...

Apart from that .... what SoH said smile

sunface Tue 19-Jul-11 13:47:54

Thanks ladies, that's a big relief. We did have the 12week scan and it was spot on date wise, so i'm guessing it is just as you have both said rather baby arriving 3weeks early!!!! Thank you!

ShowOfHands Tue 19-Jul-11 13:51:05

Honestly, try and get yourself into the frame of mind where a normal pregnancy lasts 37-42 weeks because psychologically it's MUCH easier when you go past 42 weeks and less worrying if you labour at 37 weeks.

BTW, my fundal height went from measuring behind to ahead in the course of a couple of weeks. Even having a full bladder can fiddle with the measurement. Like Knitter said, it's just a very vague tool and if it indicated anything of concern you'd have been told (and even then there's usually beggar all of note happening).

Try not to worry and congratulations!

sunface Tue 19-Jul-11 13:59:02

Thanks ShowofHands I like that approach of between 37-42 weeks, it's a nice time frame to work with!

KnitterNotTwitter Tue 19-Jul-11 17:33:16

THe other facet to this is that big doesn't equal cooked... My DS was 10lb 6oz but that doesn't mean he was in any way more ready to be born than my neighbours 6lb 4oz baby... They come when they're ready not when they're a set size...

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