Conception date help

[Annonymous24]

I need help trying to figure out when I most likely conceived.

I have irregular periods with my last one being 20th September, this would give me and EDD of 26th June however my ultrasound has given me the due date of 3rd July.

Is the ultrasound based from the likely conception date? As this would mean I conceived around 27th September which is only a few days after my LMP ended. Or do I need to add the standard 2 weeks on to that and then I most likely conceived around 11th October?

Either way am I going to be 41 weeks pregnant rather than the standard 40 as I at least know for certain the date my LMP was and that’s 41 weeks exactly from my given due date.

Very confused any advice would be appreciated as do not have another midwife appointment for a while to help clear it up

The ultrasound dates you from the 'start' of the pregnancy (i.e. two weeks before ovulation / presumed LMP). So you would hit 12wks at 10wks post-ovulation.

Once you've had a scan the LMP becomes irrelevant. The scan dates the foetus in terms of it's growth and development. So your due date should be wk40 according to your dating scan, not your lmp. That's why people's EDDs often change at the 12wk scan because there is now a more accurate way to date the pregnancy. Hope that makes sense?

In my case, I wasn't tracking the month I fell pregnant with my current pregnancy as it was straight after a loss and I wasn't bothered about trying straight away. I've had to give the date of my miscarriage bleed as my LMP and I wasn't tracking ovulation. However, since early scans at 6 and 8 weeks baby has been a week behind the dates according to my 'LMP/bleed'. This makes sense to me as I know from when we DTD that I must have ovulated later than usual that cycle.

Good luck with it all! 😊

As PP said, once you've had your dating (12 week) scan, your last period date is disregarded, as they go on the measurements of the baby as that's more accurate than last period. And always based on 40 weeks of pregnancy. There's a lot of variables around dating your last period, like noone can know for sure when they ovulated or implanted.

Using last menstrual cycle as a guide for pregnancy dating is old fashioned, inaccurate (and in my opinion ignorant) by medical staff unless you have a very textbook 28 day cycle

it sounds like you ovulated around day 21 therefore your conception date would be around October 11 like you say.

Majority of women don’t ovulate on day 14.
When my midwife asks me LMP I actually tell her an incorrect date as I know they will say I should be measuring further along if that’s the case (very frustrating part of medical appts when you have irregular cycles!)

Dont worry at all :)