Expert: Catherine Beier MS CBE - 12/21/2008

Question
I took a pregnancy test July 9th. It said no, then I took another one July 14th. It said yes. On July 21 I went to the ER and they said I was 5 weeks and 2 days. My LMP was roughly around 16 or 17 of June.(possibly). How far off could that ultrasound be? I never gave them my LMP because I wasn't exactly sure. Me and my boyfriend broke up and around July 2 or 3 I was with someone else. Could it be possible I've gotten pregnant right before my period? What about Right after..which would be around the 23rd of June? (He left about the 29th or 30th). If thats so ...then the ultrasound is off almost by two weeks! ...right? October 23rd I had another ultrasound that said 19 weeks and 2 days. What do you think? Should I be secure on the first ultrasound and say I got pregnant before July?

Answer
Early ultrasound is the most accurate way to date a pregnancy and is usually off by no more than 3 days in either direction.


Based on the information you gave, you most likely conceived around the 28th of June.


Pregnancy dating, even with ultrasound, adds two weeks (typically the time before ovulation).  This means that at the time of your ultrasound, the baby was measuring 3 weeks, 2 days (gestational age), but the pregnancy duration would be 5 weeks, 2 days.


So, it looks like you conceived soon before he left.  If you had intercourse in any of the few days prior to this, that would have resulted in your conception.



Best,
Catherine