I am trying desperately to remember the title of this book. I read it sometime between 1995 and 2004. The protagonist is a female doctor. She starts researching women who get pregnant, miscarry, and then get pregnant again almost immediately. The government gets wind of it all and is trying to track down these women. Oh, and the protagonist is pregnant by the end of the book and is on the run. It was also available as an audiobook.
I want to say it's Darwin's Radio by Greg Bear, where humanity is making a leap up the evolutionary ladder. I'd go further but don't want to spoil it for others just in case.