What causes a partial molar pregnancy?
A partial molar pregnancy is a genetic accident. In a normal pregnancy, the egg receives one set of 23 chromosomes from the father and one set of 23 chromosomes from the mother, for a total of 46 chromosomes. In a partial molar pregnancy, the egg receives two sets of chromosomes from the father, usually because two sperm have fertilized the egg. The egg now has 69 chromosomes, instead of the normal 46. Molar pregnancies occur approximately once every 1,000 pregnancies. They are more common in women who are older than 40 years and in women who have had two or more miscarriages. Partial molar pregnancies occur less frequently.
