I had unprotected sex in a 1 night stand

Patient

Q: I had unprotected sex with a 1 night stand on 24/8/14. I had the morning after pill on the 25/8/14. I got my period on 3/9/14 and it lasted 5 days. I slept with my partner numerous times during the month of September, I tested positive via a in home pregnancy test on 4/10/14. I had a scan on 6/10/14 and they told me I was around 5-6 weeks pregnant, no further. Does that make it certain that I am pregnant to my partner and not the one night stand? As I have been told you are pregnant from the 1st day of your last period. If I was pregnant to the 1 night stand, wouldnt I be pregnant from the period before that incident? Which was the 7/8/14? I had another scan at 8 weeks and again at 12 weeks and they were all in line with my last period in September. I've also been told u can't get ur period if ur pregnant but that I could have had implantation bleeding, however my period was regular, not light, and lasted 5 days as usual. I'm paranoid that even thou I got the morning after pill and had a period that there is still a chance the 1 night stand could be the father, as I heard sperm can stay inside you for a few days. Any help would be great. :)

Doctor

A:   Hello,
Thanks for the query,

It is clear that once a withdrawal bleed is seen after the morning after pill, pregnancy is ruled out completely. It was not an implantation bleed because it is in form of spotting and lasts only for 2-3 days but you had a full fledged period, hence the chances of you being pregnant from the 1 night stand is negligible.
However the scan cried that the growth was in line of pregnancy acquired in September, so all the more reason that it's your husband's. However, the best way to confirm would be to undergo an amniocentesis at 15-18 weeks period of gestation and check the foetal cells in amniotic fluid withdrawal for foetal DNA paternal matching.
I hope I have answered your query in detail,

Wishing you good health,
Regards

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