Jennifer Merrill Thompson was confident the baby she was carrying -- her second -- was a girl. After all, the mom from Vienna, Virginia, had followed the suggestions in the book How to Choose the Sex of Your Baby, which detailed how to optimally time intercourse in order to conceive a girl. So when the sonogram image left no doubt that her daughter was, in fact, another son, a shocked Thompson burst into tears. "I didn't want to be just a mother of boys," she explains.

Although Thompson says she immediately fell in love with her son, she still felt a void that could only be filled by little frilly dresses. Thompson became a mom on a mission, scouring the Internet for a way to guarantee that baby number three would be her dream daughter.

Her quest landed her at the Genetics & IVF Institute, in Fairfax, Virginia, where a clinical trial is currently under way to test the safety and efficacy of a sperm-sorting process called MicroSort. After three rounds of artificial insemination, Thompson finally conceived her little girl....