Ultrasound Accuracy: Estimating Gestation & Conception Dates - Expert Advice

Question
My finance had an ultrasound yesterday and the results say the fetus is 7 months and two days old putting conception date roughly at May 12 or 13 by our calculations.  Unfortunately I was not in the country then.  I saw her last on April 30 then did not see her again until May 23.  We did not have sex the morning of the 30th but did the night of the 29th.  I was on a ship out of the country the rest of the time.  Is there any chance the baby is mine, or is the test accurate?

Thank you.

Answer
I am assuming you mean 7 weeks and 2 days, not 7 months!

Actually, being 7 weeks and 2 days on July 2 puts the date of conception at May 26.  Remember, the baby is considered 2 weeks old on the date of conception, due to oddities in the dating of pregnancies leftover from before we knew about ovulation.  So you have to subtract two weeks from the figure the ultrasound gives you to find the date of conception.

I hope this puts your mind at ease!