If you know when you conceived then doesn’t that tell you your REAL due date?

[Itsnoteasyfeelingqueasy]

Hi, my due date is 6th July based on the date of my last period being 4th October. However I know I conceived/ had sex on 21st October, 17 days later so am I correct in thinking my baby could actually be due 17 days “late”? Or even later as although I had sex on 21st the actual conception could have been a few days later?

I’d be interested in your thoughts. I’m just worried that if I go more than 42 weeks induction will be encouraged when in fact my baby might not even be late

The pregnancy is dated from your last period but assumes that you conceive 14 days after that. So if you actually conceived 3 days later you'd only be 3 days 'late'. However there is no definitive gestation time, and everyone is different, full term is classed as anywhere from 37-42 weeks in the UK and is different again elsewhere. So you can't actually be that specific with it!
You'll get an official due date at your 12 week scan when they use the measurements of the baby to get a more accurate picture than date of last period, but again everyone is different so it doesn't mean baby will come on that date.

Sperm can live for 5 days or so, so although you had sex on the 21st it could have been any of the following four days or so when actual conception took place. It's all a bit of an estimate. At the 12 w scan they date you according to foetal size and that's the due date that sticks!

Sorry, just re-read and seen you mention conception could have been later!

No, that’s not how it works. As PPs have said, they’ll give you your DD at your 12w scan and that will be based on measurements not LMP.

@Lola871 thank you. I didn’t realise they already assumed you conceived around 14 days after the first day of your last period. That makes more sense now!

I have my official due date which is Monday 😬

I have longer cycles and started my period on 6th December. According to the "28 day cycle" I should have conceived on 20th December and I did not, I conceived on Christmas Day which I knew as I temped and tracked ovulation. I just told the midwives I started my period on 11th December so they would match my dates, which it has every time.

So close now! Sorry I completely missed that the due date was already nearly here, just went into a little spiel of explaining. Hope baby doesn't keep you waiting too long, so exciting!

@Chanel05 very smart move! I have short cycles, not sure if that would mean my due date would be sooner or later?

@Lola871 thank you. It’s hard not to get a bit obsessed with dates when it’s so close!

Human gestation is actually 38 weeks. We say 40 weeks to allow for the way dating is done from periods. So 40 weeks from your last period, or 38 from your known conception date

I know what you're saying, but it depends when your body ovulates. So you might ovulate on the day of sex or 5 days later (and the sperm stuck around!) and that's when the egg starts growing from.

40 weeks is such a rough guide anwyay, none of us are exact in how we grow.

With my first they put me a week ahead at my 12 week scan and I was like crap I’ll massively go over my due date. DS came 3 weeks early and was a perfect full term baby . Now I’m pregnant again but I only had sex once at the very end of my period . I figured they would put me a week ( or more ahead) but nope , I’m exactly on track. If this was my first baby I would be freaking out but I really don’t believe in due dates now 😝! When people ask when baby is due I just say this Fall . Baby is officially due November 16th though ! I bet I’ll go 2 weeks past my due date this time 💁‍♀️

If you have short cycles is there any way that you could have conceived earlier - like a lot earlier? Generally you ovulate 14 days before your period so if you have short cycles then you could ovulate very early on indeed.

I have 20 day cycles and we think I ovulate on day 6 as my scan moved my due date by 8 days with dd. She is basically a biological impossibility and yet she seems to be here!