My boyfriend doesn't want to claim our child as his because I had sex with my ex last Sept28, 2010. But I had my period right after. We had sex (the dad of my son) last Oct10, 2010. I immediately had transvaginal ultrasound the moment I suspected that I was pregnant, which was last Dec16, 2010. The result shows that I'm on my 11th week and 2days of pregnancy and that I will give birth on July05, 2011. I'm sure about who the father of my son is. However, my Ob said that I was already pregnant last Sept. and that I will give birth on the 30th of June. This got my boyfriend confused, so he left me. This has also made me doubt myself. Isn't the transvaginal ultrasound the most accurate exam? Do I still need to prove to him that he's the father? Please help! :(

This is a case where you will need DNA testing to know for sure.
However, odds are greater that the child is from your boyfriend for a few reasons.

You had a period right after the sex with your ex. While it is possible to become pregnant at that time, it would not be the norm. Your OB dated the pregnancy from the first day of your last period (this is normal practice), however, it would be very unlikely that you were pregnant at that point. The transvaginal ultrasound would be more accurate for dating purposes as measurements of baby are used and, early on, babies tend to develop in a uniform manner. Most often, doctors will adjust due dates from the results on an ultrasound.

It is also important to remember that due dates are not exact. This is because you simply do not know exactly when conception occurred, only a time frame of when it most likely occurred. You have a couple of weeks before and a couple of weeks after the due date which would be considered the norm to give birth. When did you actually have the baby?

Yes, you do still need to find out if he is the father or not. It is unfortunate that he was not interested enough to find out when the baby was born. Your child deserves to receive support from whomever the father is whether you are with that man or not.

I will agree, while the odds are that it is your boyfriend, it is really just too close to tell. But no, there is no way to know till the child is born and a DNA test is done

I had given birth earlier to the ultrasound result, which is last June21. I'm not surprised by the early delivery because I walked to and fro going to the office EVERY SINGLE DAY until the week before I gave birth. About the time frame of the conception, my new OB had it computed for me, and it really fits the time we had sex. She said that I shouldn't worry about it anymore because transvaginal utz never fails (especially when it's done earlier in pregnancy), but I just can't stop thinking about it. :( If you'll see my son, he really looks like my boyfriend, from the eyebrows, nose, lips, dimples, hand, and toes. All that can be proofs that the baby is his, but when my friend talked to him, he's firm enough to say that it really isn't his. He even managed to say that the only way I could make him believe me is to have a DNA test. And yes, I'll have a DNA exam. I just hope that he won't make excuses anymore when I hand him the truth. Thanks, DoulaLC!