Molar pregnancies are an uncommon and very frightening complication of pregnancy. The formal medical term for a molar pregnancy is “hydatidiform mole.” Simply put, a molar pregnancy is an abnormality of the placenta (afterbirth), caused by a problem when the egg and sperm join together at fertilization.
There are two types of molar pregnancy, complete and partial. Complete molar pregnancies have only placental parts (there is no baby), and form when the sperm fertilizes an empty egg. Because the egg is empty, no baby is formed. The placenta grows and produces the pregnancy hormone, called HCG, so the patient thinks she is pregnant. Unfortunately, an ultrasound (sometimes called a sonogram) will show that there is no baby, only placenta. A partial mole occurs when 2 sperm fertilize an egg. Instead of forming twins, something goes wrong, leading to a pregnancy with an abnormal fetus and an abnormal placenta. The baby has too many chromosomes and almost always dies in the uterus. Thus, molar pregnancies are “accidents of nature” that are not anyone’s fault. They are not caused by behavior, but they are more common in older women and in certain geographic locations. Also, although most molar pregnancies occur after a miscarriage, some occur after an ectopic (tubal) pregnancy or even a normal delivery.