Expert: Dorothy H, LCCE - 12/11/2010

Question
just wondering if a pregnancy test would show postive a week after intercourse?? reason im asking is i had a one night stand on the 8th of june this yr, and tested positive a week after,it was wen me and my hubby were on a break, the last time i had sexuel intercourse with my hubby was on 23rd may i also had a scan on the 23rd of june which told me i was only 5 weeks cud it be the one night stands baby?? also unsure of lmp. many thanks tasha

Answer
Hi Tasha,

I apologize for the long delay in getting back to you; I wound up in the hospital unexpectedly and just got home yesterday.
 
It would be highly unlikely for a pregnancy test to show a positive reading a week after conception. The fertilized egg needs to implant and start secreting HcG, which generally takes at least 10 days.

Now your ultrasound is pointing to a June 2 conception date, which doesn't line up with either one of the dates that you had sex.  Did you have any other 1st trimester ultrasounds - 5 weeks is early and usually a 7-10 week ultrasound is going to be the most accurate for determining due date.

Is it possible that the 5 week ultrasound wasn't really a 5 week ultrasound, but that they said you conceived 5 weeks ago?  If that's the case, it lines up quite well with conception occurring around May 19.

If they told you based on that 5 week ultrasound that your due date is around February 8th, then that 5 week ultrasound was really a 5 week after conception ultrasound, and then it's highly unlikely that the one night stand produced your baby.

However, if they are giving your due date as around February 22, then the only way to tell for sure is going to be to have your husband take a paternity test after the baby is born.

I hope this helped answer your question.

Sincerely,

Dorothy H, LCCE