A question about dating scans and early/late ovulation..?

[AllTheYoungDoods]

So, if your pregnancy is counted from the last day of your period, and roughly based on a 14 day ovulation, what happens if at your dating scan it's shown that you conceived earlier (or later) than then?

Say I trot in at '12' weeks and am told that I'm a week further along because I ovulated earlier (a theory I'm brewing here!) then do I go up to 13 weeks, even though that would mean I was nominally pregnant during my last period, IYSWIM?

Yes, they would use your dating scan to calculate. I think if it's just a couple of day's difference they keep with your calculation.

yes they do change it,

i went for my '12' week scan expecting to be about 12+4 and was told I was 10+4!!

I don't believe it and say im 39 weeks monday (they say im 38)

but they go by the scan. even though it makes no sense to when i concieved!

I'm not sure if I'm misunderstanding what you've written - gestation is usually estimated from the first day of your last menstrual period (LMP), not the last day of your last period.

Whether or not they adjust your EDD from LMP to your EDD from scan depends on how different they are and the policy in your PCT - round here they only adjust if the difference is 7 days or more. Best logic is to remember that they E stands for Estimated - and that "term" is a period from 37 to 42 weeks rather than a 24 hour day.

The only time its likely to be a problem is if you go much beyond 40 weeks - either because you think you're a week further along and are getting uneasy at going towards (by your dates) 43 weeks but they won't do anything as policy says 42 weeks before induction, or if you're being pushed towards an induction "because you're 42 weeks" when you think you're not that far along and don't see the need. That's a long way away yet, though, so not worth worrying about too much at the moment, especially until you know whether they want to try and move your EDD...

The scan date will be the one used, regardless of your own calculations. As said previously, it is the first day of the lmp that you count from. Also it isnt unheard of for people to carry on having periods even when pregnant.

Your pregnancy is dated from conception. Your estimated due date is 38 weeks from conception. But because the average cycle is 28 days with ovulation happening on day 14, as a preliminary date to work from they count 40 weeks from the beginning of your last period. It's a rough guide and the dating scan (which is accurate to within 5 days either way) provides a better picture of your actual situation.

It's dated from the first day of LMP so calculations from this method mean that the first few days of all pregnancys are spent having a period (unless of course there is a wildly irregular cycle involved), you then have a bit where you aren't pregnant. Put together this roughly equates to around 14 days. But because ovulation and time it takes sperm to reach egg can vary by a few days there is a reasonable margin of error in this method. Although as someone else said you're only ever going to get an estimated due date.