When Melissa Hiltbrand of Ammon, Idaho, discovered she was pregnant in 1998, her first reaction was one of surprise. "This was an unplanned pregnancy," she says. "But once the initial shock wore off, my husband and I were thrilled to be expecting our first baby."

Like all expectant moms, Hiltbrand started planning and dreaming of the day she would hold her baby in her arms, but her pregnancy was difficult from the beginning. "For 16 weeks, I had extreme morning sickness and fatigue, as well as consistent spotting," she says. These symptoms concerned her doctor, who ordered an ultrasound to find out what was wrong. When Hiltbrand received the results, they were more shocking than finding out she was pregnant. The diagnosis was a hydatidiform mole, also known as a molar pregnancy.

"Molar pregnancy is a very confusing and complicated disease," says Dr. Naomi E. Stotland, an OB/GYN at the University of California, San Francisco. "If you receive this diagnosis, make sure your doctor spends a good deal of time explaining it to you and answering your questions."

There are actually two types of molar pregnancies: complete and partial. In a complete molar pregnancy, there is no fetus, only an abnormal placenta that is large and swollen. "Partial molar pregnancies can occur where a fetus will form," Dr. Stotland says. "But the fetus is usually abnormal and dies early in the pregnancy." It is estimated that, in the United States, molar pregnancy occurs in one of every 1,000 to 1,500 pregnancies.

"[Molar pregnancy] is caused by genetic problems that occur when the sperm and egg come together," says Dr. Stotland, who adds that it is not clear why this abnormal fertilization takes place. And although molar pregnancies are slightly more common in women older than 40, there are no real risk factors, according to Dr. John Repke, professor and chairman of the department of OB/GYN at Nebraska Health System and the University of Nebraska Medical Center.

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