Are dating scans accurate to date of conception?

[YOLO1985]

Are dating scans accurate to date of conception or do they add 2 weeks on like the doctors do? i've read so much different stuff online and im confused!

 

[ticking.clock]

no they are a guide and can be up to a week wrong either side of your actual conception date

 

[Ran]

The 2-weeks-added thing is pretty constant. Any time someone says you're X weeks pregnant, the baby's been in there for X-2. This is a useless dating mechanism for people with long cycles, especially if you have a doctor that doesn't believe long cycles exist, but you just have to roll with it.

 

[susan_1981]

They would add the 2 weeks. So they add the 2 weeks before you ov x

 

[PG5K]

I've just had an early scan at 6+5. My sonographer said she thought 5+5 but only because where it was she couldn't measure.
I know for definite that it can't be a week out as we inseminate.
I think they know better at the 12 week scan.

 

[Jac.]

Count from the day of your last period. ei, my last period was January 2nd so I am about 6 weeks and 2 days pregnant.

 

[YOLO1985]

I've just had an early scan at 6+5. My sonographer said she thought 5+5 but only because where it was she couldn't measure.
I know for definite that it can't be a week out as we inseminate.
I think they know better at the 12 week scan.

Iv had my 12 week scan and its confused me even more. And google is not a good tool to get an answer!x

 

[josephine3]

I want to know whether its from conception OR implantation!!! (+2 weeks of course!)

 

[ticking.clock]

conception

 

[TheSmpsns]

They do count it from the day of your last cycle, so not the day of conception. I know my exact date of conception (because we were NTNP that month to take a break after 11 months TTC) and we only DTD once. But all of the scans I have had say I am a little further along. Doc says it is likely because the baby is measuring longer than normal. I figured my baby will always measure long (DH is 6'9").

 

[Jac.]

6'9"!!!! Are you tall? I'm 5'11" and I think my husband is short at 6'2" haha...but 6'9"!!! geez.

 

[josephine3]

I also know the day of conception but my dating scan says +2 days on top of that.. which is why i ask is it from conception or implantation as maybe if its from implantation we could have caught from a much earlier bd, maybe taking 5 or 6 days to implant... but if its from conception itself (+ the 2 weeks) then my baby is 2 days big! x we only dtd twice that cycle so it has to be one or the other, and im pretty darn sure its the second.

 

[TheSmpsns]

I'm only 5'3". So... I'm very short in comparison!

 

[daydreaming22]

Its actually 2 weeks from Ovulation (conception). Implantation varies but the baby (cells at this point) is still growing at the same rate. Late implantation does not cause the dates to be off, contrary to what some women have posted in 1st tri.

 

[ticking.clock]

yes the cells start to divide well before the blastocyst implants, which is roughly around 5/7 days later but can happen later....
so by the time of implantation your baby is already about a week old, and you are around 3 weeks pregnant

hope that makes sense.

anyway scans are only a guide on gestation, i know the EXACT date i ovulated (as i used a donor) so i was charting my temps and scans can be 5 days out either side.

 

[josephine3]

brilliant i finally got an answer to this!! So the scan measures from conception + 2 weeks. xx

 

[chocolatecat]

Conception + 2 weeks. Mine's an IVF one, so we know to the day (hour even!). I've been measuring 2 days ahead for 4-5 weeks now. So although it's not far off, it's not perfect!

 

[moments]

What does the conception + 2 weeks mean?
If i wa 13 weeks at dating scan does this then mean baby only really 11 weeks old?
Do scans not go from conception + 40 weeks?

 

[ticking.clock]

What does the conception + 2 weeks mean?
If i wa 13 weeks at dating scan does this then mean baby only really 11 weeks old?
Do scans not go from conception + 40 weeks?

Yes baby will be 11 weeks, but you are 13 weeks pregnant,
Pregnancy is 38 weeks from ovulation x

 

[moments]

Is this also in UK ultrasound dating?