Expert: Catherine Beier MS CBE - 9/28/2009

Question
QUESTION: Iam 13 weeks pregnant and as the calculations from my doctor seems I conceived sometime around 06/24/2009, they gave me a due date for 4/1/2010 it makes sence the only problem is that me and my husband were sort of having problems and had separated around a couple of weeks after, I had some sort of sexual contact with another person on 7/10/2009 im scared that the ultrasound may be wrong and this other man may be the father of my baby.

ANSWER: Rosa,

No, it's not possible.  Early ultrasound is the most accurate way to date a pregnancy and is accurate within +/- 3 days.  As those conception dates would be more than 17 days apart, it's not possible for the ultrasound to be off that much.



Best,
Catherine

---------- FOLLOW-UP ----------

QUESTION: let me ask you another question? can a home pregnancy test give positive if im only 2 weeks and a half? or would the hormone level be to low?

Answer
Rosa,

It depends upon how you are coming up with 2.5 weeks - from conception or from the first day of your last period.  


Since pregnancy is typically calculated as 40 weeks from the first day of your last period, you aren't really even pregnant for the first 2 weeks, since ovulation and conception don't typically occur until about 2 weeks before the end of your cycle.



If you mean 2.5 weeks after conception, then yes, it's entirely possible.  This is when most women find out they're pregnant.  Since ovulation/conception typically occurs about two weeks before your next period is to begin, you'd be a few days late.  But, you also wouldn't be consider 2.5 weeks pregnant - you'd again calculate from the first day of your last period, meaning you'd probably be somewhere between 4.5-5 weeks pregnant.


Best,
Catherine