fertilization Date - Help needed.

[hayls9335]

I had an early scan today, they measured me at 5 weeks. 5 weeks doesnt add up because my partner was away on business (no there isnt any infidelity involved)
anyway, to the date he came home and we had sex it would make me 4 weeks 4 days pregnant today.
However my last period was on the 8th of july, and my missed period was on the 6th of august which would mean that if i am 4 weeks pregnant that i conceived 2 days before i was due on my period, the period that i missed.... is that even possible??!!
it would make alot more sense that i am 6,7 or 8 weeks pregnant im so confused and i really had my hopes up that i was nearly out of "danger zone" week 12 and that i could announce it, but ive just been knocked back im heartbroken.
i have another scan in 2 weeks which should tell us more, but im worrying now that my partner thinks the baby isnt his because the doctors might have screwed up the dates, i know theres no way to be 100% certain on dates but this just totally does not add up at all and he doesnt understand that.

Implantation and fertilisation can take several days after you have sex. The sperm can float around for a few days, then meet the egg, then float around a while more before burying into the womb lining.
If you were ttc did you not realise this? I don't think I've ever heard of someone being suspected of infidelity for being a few days one way or the other on an early scan!

I think It's entirely possible that in the month you got pregnant that you ovulated late and that you could be 4w4d & they've not been that accurate in the measurements?

Last time I had a friend who had such irregular cycles that over the pregnancy she was given 2 due dates a month apart!

Tell your partner women's bodies are strange things & also that semen can oddly hang around for what seems like a crazy amount of time waiting for an egg to fertilise too. Last time when I showed my oh the positive stick he said "but we've not done it enough" Well that baby is now 3 & is very clearly his product! Conception is a marvellous thing!

If they're measuring you at 5 weeks, the measurements are so tiny (millimetres) that it's easy for them to be out date wise.

You can have sex and get pregnant up to 7 days later due to lifespan of sperm.

They will measure the size of the baby at this point and give you a date. This could be changed at the 12 week scan as baby will be easier to measure.

Its perfectly possible that you got pregnant from sperm left "waiting around" from before your dp went away (some strong sperm can hang around for upto 7days, then sperm could have met egg and they may have floated around for a few days before implantation and thus actual conception).

Equally you can get pregnant directly before a period (its even possible whilst your actually on a period).

Plus id expect youre dates to move by 3/4days easily by the 12 week dating scan (they can only acurately date in the few weeks surrounding 12w).

Also, just to make sure you know that you concieve 2weeks into the pregnancy (based on the average womans ovulation from last period - dating scans still add on these 2weeks before actual conception). So 5 weeks pregnant would mean 3 weeks since conception.

Ovulation varies from woman to woman and if you never tracked yours you might be a late ovulator- I have a 36d cycle and usually ovulate around 20d. Using the date of your last period is an arcane practice that the medical profession should really give up on! Even with my 12 week scan the dates they have given me must be wrong as I know when I ovulated- and actually (despite the sonographer saying 'it was really accurate') at that point the scan is only accurate to within 5 days. I am telling everyone when my baby is due based on my ovulation date, not when the scan said! Could account for why do many women go over on their dates! And is also why I will be resisting induction when they say I am due :)

Kitty week 12 is done on the development/size of your embryo. No one bar those who have ivf can tell exactly when their embryo implanted - 4-10 days after conception variation each time. Not all pregnancies last the exact same time, which has far more to do with why most (80%) are born 39-41 weeks. The fortnight leeway is nothing to do with conception in most cases: just as with everything bodies and babies vary.

Lmp is very useful in early pregnancy as a rough "ball park figure" and no hcp use it as anything more significant.

My dates were off, 8+6 scan dated exact then 12+5 scan dated me 13+5 which is impossible as a week before I had period, anyway that's the date the nhs based my EDD on, the 20+5 scan (my dates 19+5) dated me at 21weeks so another few days added on, since then I've measured on 90th line fundal measurement wise so just tells me he's always measured big.

I don't think measurements can be exact, they do it based on clicking a computer mouse from point to point, so much variation.

Now 39+6 needless to say I'm expecting to go overdue

squizita my point really was that the more variables you take out the more accurate things become. There is less variation for ovulation date than from LMP and even less for ultrasound but it's still not 100% accurate (which is what my sonographer said!) I also had a friend whose EDD put her conception 2 weeks before her husband was in the country- not great for marital harmony! For this reason the OP should not get stressed out if her 'dates' are wrong for her.
I read up on this at the time of scan and 5 days is what I found for accuracy of scan. I have just done another search and could only find 7 days!

Predicting delivery date by ultrasound and last menstrual period in early gestation.

AuthorsTaipale P, et al. Show all Journal
Obstet Gynecol. 2001 Feb;97(2):189-94.

Cereal - you can still bleed though - I had what I thought was a light period for me (and my AF was usually a heavy one) when I was 5-6 wks pregnant. It was only my feeling that something wasn't quite right that made me POAS at 7 weeks to come back with a BFP.

But yes OP - you don't conceive until roughly 2 weeks pregnant, the first 2 weeks (approximately) from LMP are body gearing up for egg being released, etc.