molar pregnancy

Molar pregnancy arises from abnormal fertilization events leading to trophoblastic hyperplasia. A complete mole results from fertilization of an empty egg by one sperm that duplicates its DNA (46,XX, entirely paternal genetic material) or by two sperm (46,XY); there is no fetal tissue, diffuse villous edema, and diffuse trophoblastic proliferation. A partial mole results from fertilization of a normal egg by two sperm (69,XXY triploidy), with some fetal tissue present, focal villous edema, and focal trophoblastic proliferation.

Clinical features include first-trimester vaginal bleeding, uterine size greater than dates, markedly elevated β-hCG (often >100,000 mIU/mL), hyperemesis gravidarum, early-onset preeclampsia (before 20 weeks—should raise suspicion for molar pregnancy), and theca-lutein cysts due to hCG stimulation. Ultrasound classically shows a 'snowstorm' or 'cluster of grapes' appearance without a fetus (complete mole) or with an abnormal fetus (partial mole).

Management involves suction curettage (D&C) with serial β-hCG monitoring until undetectable to ensure resolution and detect malignant transformation. Complete moles have a significant risk (~15-20%) of progressing to invasive mole or choriocarcinoma, whereas partial moles have a lower risk (~5%). Contraception is recommended during the monitoring period to avoid confounding a new pregnancy with persistent/recurrent disease. Chest X-ray may be performed to screen for choriocarcinoma metastasis (lungs are the most common site).

Key associations for boards: complete mole = 46,XX or XY, purely paternal, no fetal parts, higher malignant potential, higher hCG levels; partial mole = triploid (69,XXY), fetal parts present, lower malignant potential.