Confused on dates, anyone help?

[licoriceGreen]

I've just had my dating scan and I'm 11 +1 but someone said that means I'm actually only 9 +1 because they always add 2 weeks on to the date. Anybody have any idea if this is true? And if so why they do it?

Yes it's because the date they use in all maternity notes etc is weeks / days from your last period, whereas in fact you will have conceived in the middle of your cycle (normally about 2 weeks later). But when you're reading stuff about 12 weeks being a 'safe' point re miscarriage, or how big the baby is at 10 weeks etc, they are using the same weeks as your midwife / the scan - so for all intents and purposes you are 11+1 and that is the date you should use when reading up on your pregnancy etc.

Does that make sense?

No, you are 11+1 don't worry. When you first fall pregnant, you are already classed as 4 weeks pregnant when you find out. But really, you are only 2 weeks as its 2 weeks since you ovulated, but they date a pregnancy from your last LMP, as they don't know exatly when you ovulated. Becuase of that they can adjust by 2 weeks either way, but mostly they don't need to

I don't think I explained that very well so I hope you understand what I mean

It is true but whether your 'real' date is x or y is a bit irrelevant. I was confused about exactly the same and it boils down to - they say you are 11+1 when you are 9+1 from conception, on the assumption that most people's cycle in which they become pregant starts about 14 days before they conceive (not true if your cycle is long of course). So the convention is to use this date as the start point not the date of conception. So pregnancy lasts 38 weeks but at 38 weeks your dating will be 40 weeks. Does that make sense? No, not really, but any dates you see will refer to conception date minus 2 weeks as the notional start point.

Dates in pregnancy are measured from the last menstral period, assuming the average women ovulates (and at this point concieves) two weeks later. So the first two weeks of the 40 weeks of pregancy are prior to ovulation and conception, but it is tradition to measure from the first day of the last menstral period. So you are (assuming scan is right and that you ovulated at the average 14 days later) 11 weeks and 1 day from your last menstral period, 9 weeks and 1 day from ovulation (and conception - although intercourse may have been up to a week beforehand).

So you are 11 weeks pregnant.

Thank you chessy I think I understand. So I actually conceived 9 weeks ago but when I'm looking for info on development I look at 11 weeks?

yes, first 2weeks of teh pregnancy you are not actually pregnant as counted from the first day of your period, but, althugh a bit odd, this is the convention used everywhere, so you are 11 weeks!

Whoops - I see others beat me to replying¬!!!

Thank you all, I get it, this being pregnant stuff is a whole world of learning. Thanks for making it clearer

Yep OP that's exactly right, development wise your baby is 11 weeks. - congratulations by the way!