Navigating a Boyfriend's Ex-Girlfriend's Pregnancy: A Doctor's Perspective

Question
Dr. Rappaport,
This is going to sound like an episode of Jerry Springer.  I apologize in advance.  
I have no children, and the date of the first day of my last menstrual period was august first.  

Now, I met the man I am going to marry.  Yesterday, my boyfriend received a call from a friend who had heard that she has been telling people she knows he knows that she is pregnant with his child.  He called her soon after to see if the rumor was true.  When they broke up, she told him she thought she was pregnant (about two months) and she went to the doctor to find out.  She told my boyfriend after her exam that she was NOT pregnant, that there was NO baby, and he didn't need to worry about it.  They haven't had sex since then.  
By the way, I am 21, My boyfriend is 23, and the ex girlfriend is 19.  I know that birth control isn't always 100% effective, but for what it's worth, she was on birth control (the ring) the entire time they dated.  

She now claims to be 6 months pregnant, but hasn't even said anything to my boyfriend (whom she claims is the father).  If he hadn't called her last night, there would have been no information given to him about the pregnancy.  We still don't know if she is actually pregnant.  She has since moved to Illinois, while we are in Ohio.  My boyfriend of course, wants a paternity test if she is in fact pregnant.  She refused to get a test until the baby was born, which means three months of hell for my boyfriend (not to mention me).  

Technically, it is possible for her to be pregnant by my boyfriend.  That doesn't explain the story that she was pregnant when they broke up.  If she was not pregnant by him then, there is no way she could be pregnant by him now, if there has been absolutely no sexual contact between them since.  Is this correct?

Is there anyway my boyfriend can get a paternity test before the baby is born if she doesn't want to?

Any additional information you could provide us with would be helpful.  I'm doing my best to be supportive, and I know he is not blameless in this situation.  

Thank you very much,
Allison

Answer
Everything you mention is just supposition. It is impossible to tell if  and when your boyfriend had sex with this woman. First you have to find out what the date of the first day of her last period was. A sonogram can tell you exactly how far pregnant she is (if she agrees to it). A paternity test can be done, but she has to agree to it because it involves getting fluid from around the baby as well as from her mouth and your boyfriend's mouth. So if she does not want to have it done, it cannot be done. HOwever, after the baby is born, a paternity test can be done. It may need a court order, but then you will know. There is no way you can prove that your boyfriend did or did not have sex with her.