A molar pregnancy is a rare type of abnormal pregnancy caused by errors in fertilization that result in an incorrect number or origin of chromosomes. There are two main types: complete moles, which have two sets of paternal chromosomes and no maternal DNA (usually due to duplication of a single sperm in an empty egg), and partial moles, which are typically triploid (three sets of chromosomes) and result from fertilization by two sperm. Molar pregnancies do not develop into a viable fetus and are associated with abnormal placental growth. While rare, they can pose health risks and require monitoring after treatment.
