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Date from scan or last period?

(8 Posts)
plentyofsoap Thu 16-May-13 12:11:03

Hi, I had a scan last week that put me at 10+3. She stated in the scan that she would date just in case I decide not to have another scan at 12 weeks. I saw the midwife at booking in on tuesday who stated that she would use the first day if my last period. That is fine, but there is over a weeks difference between the two. I am therefore confused which is currently not difficult to do! What date would you use?

BraveLilBear Thu 16-May-13 12:19:51

As far as I know, scan dates overrule LMP dates.

In my case, mine match 'exactly' - even though I know I ovulated seven days later than usual so my dates are a week out (early) compared to mine. More surprisingly, every scan and measurement has also matched the scan/lmp dates exactly so I'm worried less about it for now (though if it comes to induction I may kick up a fuss then!).

PurplePoppySeed Thu 16-May-13 12:29:19

All of my notes have both dates, LMP is a week earlier than scan estimated dates. MW advised me to go with the later date but no one has particularly held me to either yet - I'm sure that will change towards the end though!

Teaandflapjacks Thu 16-May-13 12:30:55

I have this - my scan puts me a week behind my dates based on my period. However my later scans showed baby was back to my dates. my doctor wont change the due date , my next scan is my 30 week scan (I live in Germany - we have more scans here), if at all necessary - she says there is a room for error each side. I think it is important if you go over and then they start looking at inductions etc, like Brave says. Congrats!

MrsBri Thu 16-May-13 12:34:02

My scan date is 4 days earlier than my LMP / known ovulation. I wasn't given a choice which date was used, as the midwife entered the scan date into my notes for me as the agreed date. I'm happier being moved forwards than backwards, so will accept that as the one we use.

Baby seems to be tall anyway, so I don't want him / her squished in for too long in any event! :-)

plentyofsoap Thu 16-May-13 12:43:43

Thank you. Maybe it will equal out more later on?! Due to bleeding which has thankfully now stopped it was my third scan and they have all been ahead of my dates. With the last baby being early I have not even considered going overdue or an induction grin

MrsBri Thu 16-May-13 13:02:55

Don't count on bump now measures 2 weeks ahead of dates!

I know it's not an exact science, however, and I think baby is just long. Or that's what I'm hoping!

And when you hear how wrong people's growth scans have been in late pregnancy, I'm beginning to think it is all guess work anyhow!

Circaea Thu 16-May-13 13:14:23

It depends on how sure you are about your LMP date and cycle - the closer you are to a 28 day cycle, ovulating 14 days before your period, the more likely LMP is to be accurate, because that's how it's calculated. Some LMP calculators will adjust for cycle length.

Scans in the first trimester are usually +/- 5 days accurate. So you need to average out the two in terms of confidence level and agree a date with your midwife based on the available information.

There's no perfect method that can tell you an exact fetal age, and in any case pregnancies aren't all the same number of days long so even if you knew exactly how far along you are now it doesn't guarantee a due date.

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