A molar pregnancy is a rare complication of pregnancy that occurs when abnormal tissue grows in the uterus instead of a normal embryo. This can happen when the fertilized egg has an incorrect number of chromosomes, leading to the formation of a mass of cells called a mole. There are two types: complete and partial, with complete moles containing no normal fetal tissue. Symptoms of a molar pregnancy may include vaginal bleeding, rapid growth of the uterus, and severe nausea. Diagnosis is typically made through an ultrasound and blood tests measuring human chorionic gonadotropin (hCG) levels. Treatment usually involves removing the abnormal tissue to prevent complications.