Patient: I am facing a dilemma. I’m currently 16 weeks and 2 days pregnant and am unsure who the father of my baby is. I’m a married woman, but slept with another man once while my husband and I were having problems. I slept with the other man between April 1st and 4th (unsure of the exact date). On the 4th of June I was told I was 7 weeks and 4 days pregnant with an estimated due date of the 17th of January by having an ultrasound. My periods are very irregular so this was the only way I could find out how far along I was – I had not had my period since around February. I was told at my 12 week scan that the baby’s growth was consistent with this due date. Do you think there is any chance the baby could belong to this other man? Does the fact that I am irregular affect the general timing of conception? Help!
Doctor: I understand that your cycles are irregular and because of that the best test that you could have done was taking the ul trasound and at the same time a blood pregnancy test to estimate your gestational age.According to your ultrasound the most probable day of conception might have been on June 13th, however you must know that this is not 100% accurate, many differences in each woman’s cycle may hinder the accuracy of the conception date calculation using the results form an ultrasound. The viability of sperm varies as well, which means that intercourse three to five days prior to ovulation may result in conception. Ultrasound dating of conception is not reliable for determining paternity because the ultrasound can be off by at least 5-7 days in early pregnancy. Certainly if you also had sex with your husband a week before June 13th, this could increase the chances that your baby belongs to your husband.