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Pregnancy

Talk about every stage of pregnancy, from early symptoms to preparing for birth.

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Original poster

dating scan put conception during week of no sex?

24 replies

wildpoppy · 14/04/2015 22:33

So the scan today said I am a bit further on than I thought - just three days, but if I was that far on then it's immaculate as dh was away that week so the earliest we could have conceived even if sperm met egg the second he walked in the door would mean I am two days less pregnant than the dating scan. Are they ultra accurate?

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HoppityVoosh · 14/04/2015 22:40

I can't comment on how accurate the scans are but I think it's meant to measure how big the baby is rather than how many weeks since conception. They won't always match.

WannabeLaraCroft · 14/04/2015 22:44

They always date from the first day of your last period. I definitely didn't have sex while on my period! It's more to do with size and growth of baby, not really accurate on when baby was conceived, iyswim?

I totally didn't understand when I was pregnant with my first, but I get it this time round. I'm just over 10 weeks, but logically I know that conception occurred after then so really only about 8 weeks. Sorry if that doesn't make much sense!

TobyLerone · 14/04/2015 22:51

That's not how it works. It all depends on when you ovulated etc.

Fattycow · 14/04/2015 23:01

My OH and I had sex on a Wednesday and on the next Sunday, as I was abroad on the days between. I conceived on the Friday I was abroad. This is very possible, as sperm can live up to a week. I know I ovulated on the Friday, due to keeping track of ovulation for a while. So you would probably have gotten pregnant from sperm that entered before your DH went away.

The dating scan measures the baby. In the early weeks (until 13 weeks), they grow at a predictable rate, so all babies of for example 8 weeks are the same size.

happygojo · 14/04/2015 23:03

I was put a full week ahead at my 12 week. If that had been exactly right it would have meant I conceived on a Monday on my period, before we had agreed to 'try' Babies just grow at different rates, I know I conceived the weekend after

HoneyDragon · 14/04/2015 23:06

According to my dating scan I conceived when dh was in Italy for two weeks

anxiousannie10 · 14/04/2015 23:19

My dating scan and Lmp have put me a week and a few days further on than I actually am. I know when I ovulated and had sex, according to them I got pregnant whilst on my period ! Which is of course wrong. their dates are wrong but all they say is, we have to go by your last period. Frustrating.

TobyLerone · 14/04/2015 23:20

You don't conceive 12 weeks before your 12 week scan. You conceive roughly 10 weeks before. Your pregnancy is dated from approximately 2 weeks before ovulation because they go from day 1 of your cycle. Ovulation usually happens around day 10 - 15. You can't get pregnant until you've ovulated.

MrsRossPoldark · 14/04/2015 23:30

I shouldn't let it worry you. They're never 100% accurate! Even further on, scan with DS1 said I was having a big baby, but he was only 7lbs 1! Earlier on, I was never led to believe it was that accurate. What's a few days?!

toohardtothinkofaname · 15/04/2015 06:49

What happens if they date you later and it's incorrect? Would you get induced even if technically you're not over or would they move it back once they see size of baby? Or panic you saying it hasn't grown enough?

Ie. Ovulate CD40 so only 2 weeks since conception but they put you as OVing CD14 & think you're 3+5 since conception.

S2b16 · 15/04/2015 07:01

I concieved while I was in another country without My partner according to scan.....but baby had caught up to our original date by 20 week scan.

Flossieflower01 · 15/04/2015 07:04

Someone I know who had ivf twice had her date moved by a week at the 12 week scan both times and she knew to the minute when she'd conceived! Bonkers.

Minitant · 15/04/2015 07:15

You can conceive up to three days after you have sex...

hestialou · 15/04/2015 07:25

My dating scan put me a week ahead, I had been dating from LMP, but due to charting knew when ovulated and dates of sex, none of these tie back to dating scan so I think just a slightly bigger baby.

Littlemisssunshine75 · 15/04/2015 07:38

Dd was always a few days ahead of dates from the very earliest scan. However, we knew the moment of conception as she is an ICSI baby - she was just growing well

Number3cometome · 15/04/2015 11:19

I've had my date changed twice and I know for a fact it is still wrong as I had a progesterone test which showed I did not ovulate at the time they say I was pregnant. It's only an estimate, just go with it, it won't make much difference in the long run.

NakedBaby · 15/04/2015 11:22

For historic reasons, pregnancy is counted from the first day of your last period.

Hence the scan will quote: time baby has been growing + 2 weeks.

Additionally - sperm and eggs can hang around before conception - so sex day doesn't have to match conception day.

RugBugs · 15/04/2015 11:30

Mine was based on femur length. Past two pregnancies (both delivered early) due date was brought forward by 3 days from lmp which is about right, I have slightly shorter cycles and know when I ovulated. This time I was put forward by six days.
I noticed at 20wk scan that based on femur length it was back to same as lmp.
This baby had better be early too or I run the risk of being induced on DD2's birthday.

Original poster

wildpoppy · 15/04/2015 16:49

Yes I know you can conceive after sex depending on ovulation but according to 12 week scan (based on crown to rump measurements) I conceived before I had sex!

OP posts:

TobyLerone · 15/04/2015 17:28

But the dating scan doesn't tell you anything about when you conceived

NakedBaby · 15/04/2015 17:33

It just means your cycle is off - or their measurements were a bit off.

LadyCatherineDeTurd · 15/04/2015 19:08

Unless you have IVF, you don't actually know when you conceived. You may know when you had the sex, but not necessarily when sperm met egg. It can take a few days.

newbian · 16/04/2015 03:28

Obviously the scan is wrong wildpoppy, I wouldn't unduly worry about it. We tend to think that living in 2015 science has all of the answers. It doesn't. You obviously conceived at some point when it was possible for you to do so, regardless of the fetal measurement that appears on the scan.

earlytwentiesmama · 05/03/2021 16:33

Do ultrasounds in the UK add 2 weeks on to the feral age? So if your scan says you are 10 weeks pregnant did you actually conceive about 8 weeks ago? TIA. X

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