Molar Pregnancy
On this page
Direct answer
Molar pregnancy (hydatidiform mole) is a gestational trophoblastic disease in which abnormal trophoblast proliferates and converts chorionic villi into grapelike vesicles, with excessive human chorionic gonadotropin production. The complete mole is diploid, entirely androgenetic and father-derived with no fetus, whereas the partial mole is usually triploid with fetal tissue and focal villous change. Painless bleeding with a uterus large for dates, very high hCG, hyperemesis or pre-eclampsia before 20 weeks and a "snowstorm" ultrasound lead to suction evacuation, then serial hCG surveillance because a minority progress to neoplasia.
What you must remember
- Complete mole: diploid karyotype (most often 46,XX) with entirely paternal nuclear DNA, no fetus or fetal red cells, diffuse villous oedema and trophoblastic hyperplasia; progression to persistent trophoblastic disease in roughly 15-20 per cent.
- Partial mole: usually triploid (69,XXY or 69,XXX) after fertilisation by two sperm, with fetal tissue, focal villous swelling and focal trophoblast proliferation; post-molar neoplasia is uncommon (under about 5 per cent).
- Risk factors: extremes of reproductive age (especially 40 and above) and previous molar pregnancy.
- Clinical features: painless vaginal bleeding is the commonest symptom; uterus large for dates in roughly half of complete moles, hyperemesis, pre-eclampsia before 20 weeks (a red flag), hyperthyroidism from hCG and passage of vesicles; theca lutein cysts may be large and bilateral.
- Diagnosis: transvaginal ultrasound — a complete mole shows an echogenic "snowstorm" uterus without fetal parts, a partial mole a fetus with cystic placental spaces; histopathology confirms; beta-hCG is typically markedly raised (often above 100,000 mIU/mL).
- Treatment: suction evacuation is the method of choice; medical induction is generally avoided for fear of trophoblast dissemination and haemorrhage; hysterectomy is an option for older women not wishing fertility; prophylactic chemotherapy is not routine; Rh-negative women receive anti-D.
- Follow-up: serial beta-hCG every one to two weeks until undetectable, then monthly for six months, with reliable contraception; pregnancy is deferred for six months to a year per protocol.
Common confusion
The complete versus partial contrast is the perennial stem: diploid androgenetic without fetus versus triploid with fetal tissue, diffuse versus focal villous change, high versus lower risk of neoplasia. The clinical trap is pre-eclampsia or hyperthyroidism before 20 weeks — both should trigger an ultrasound looking for a mole, not treatment of blood pressure or thyroid alone. Bilateral theca lutein cysts are benign hCG-dependent cysts that regress after evacuation and must not be operated upon.
Exam-focused takeaway
Expect karyotype-and-histology matching, the snowstorm ultrasound and the association of very high hCG with hyperemesis, early pre-eclampsia and hyperthyroidism. Management questions centre on suction evacuation, anti-D for Rh-negative women and the serial hCG follow-up protocol with contraception. The 15-20 per cent versus under 5 per cent progression figures separate complete from partial moles in one-liners.
Frequently asked questions
How do complete and partial moles differ?
Complete moles are diploid and androgenetic without fetal tissue and carry a 15-20 per cent risk of persistent disease; partial moles are usually triploid with fetal tissue and rarely progress.
What is the classic ultrasound of a complete mole?
An echogenic "snowstorm" or "bunch of grapes" pattern filling the uterus with no fetal parts, confirmed histopathologically after evacuation.
Why can a mole cause pre-eclampsia before 20 weeks?
The trophoblastic mass produces disease through its size and hCG output; pre-eclampsia before 20 weeks is distinctly unusual in normal pregnancy and should prompt suspicion of a mole.
How is a molar pregnancy treated?
By suction evacuation of the uterus (with anti-D for Rh-negative women), reserving hysterectomy for selected older women; prophylactic chemotherapy is not routine.
What follow-up is needed after evacuation?
Serial beta-hCG every one to two weeks until undetectable, then monthly for six months, with reliable contraception during surveillance.