Accuracy of dating U/S?

xinabride

So I finally had my first appointment at 10w4d by my calculation. The doctor took the babies measurements and said I was at 9w1d but because DH and I were living 500 miles apart in June so I know conception was during a 5 day window we saw each other that would but me around 10.5 weeks about. 

I'm wondering if I should keep track of my date instead of the doctors for myself since I am 100% certain she is off.

ceh789

+/- a week really doesn't make that big of a difference .  My conception date (known to be 1 of 3 days) is a week off of my dating ultrasound - the OB said we could use whichever I wanted.  I used the later date to time scheduling my genetic screening/NT scan so I don't go in and have them say I was too early but in my head I'm using the earlier date that I know is right.

katykatykaty

She's not really off...  she's just going by the measurements of the baby.  Did you tell her that you expected to be farther along and about your husband being gone? 

xinabride

Unfortunately I didn't get a chance. They called me in early so it was a rush, I think she had an emergency or birth. I'm going to ask her during my next appointment which is scheduled to be longer. I'm going to probably go with my end of first tri date to relax instead. Just more peace of mind for myself.

Gamera3000

I know the conception date in a two-day period. I suspected that I got pregnant from ovulating early since it wasnt long after my period. The u/s technician confirmed that was what happened because the baby measured 8w5d instead of 8w1d. I use the earlier date personally since that corresponds with the actual size of the baby but "officially" it's the later date.

amberlynnr7

I'm wondering the same thing. I didn't really have a problem with DD but this one is about 6 days behind. The tech didn't say anything about changing my date but I haven't seen the doctor again yet.

bunniekrissy

Well, you can actually conceive up to 7 or so days after last having sex, if that is when ovulation occurs. It is possible, though unlikely, for sperm to hang around and live that long under the right conditions. If that were the case you wouldn't be as far along as you thought.

However, I was charting and I am pretty much 100% sure of my dates (I have charted 1 year's worth of cycles to avoid pregnancy and 6 month's worth to TTC between this and last pregnancy so I am very familiar with my body's signs) and my LO was measuring 5 days ahead. So I really believe the dating ultrasounds are not completely accurate, especially past 7 weeks or so.