Molar Pregnancy (Hydatidiform Mole)
Summary
A molar pregnancy (hydatidiform mole) is a type of gestational trophoblastic disease (GTD) involving abnormal proliferation of trophoblastic tissue (placenta) following abnormal fertilisation. Complete moles have no fetal tissue and are entirely paternally derived (empty egg fertilised by duplicated sperm, 46XX). Partial moles have some fetal tissue and are triploid (egg + 2 sperm, 69XXY). Molar pregnancies present with vaginal bleeding, excessively high hCG, uterus large for dates, and classic "snowstorm" ultrasound appearance. Treatment is suction curettage. Importantly, there is a risk of persistent GTD or choriocarcinoma, requiring follow-up with serial hCG monitoring until levels normalise and registration with a specialist centre.
Key Facts
- Complete Mole: 46XX (paternal only); no fetus; higher malignancy risk
- Partial Mole: 69XXY (triploid); may have some fetal tissue; lower risk
- Ultrasound: "Snowstorm" or "Bunch of grapes" appearance
- hCG: Excessively high (can cause hyperemesis, thyrotoxicosis)
- Treatment: Suction curettage (evacuate uterus)
- Follow-up: hCG monitoring; register with specialist centre
Clinical Pearls
"Snowstorm on Ultrasound": The classic appearance of complete mole — multiple echogenic vesicles filling the uterus.
"Excessively High hCG": hCG levels are much higher than expected for gestational age (often >100,000). This can cause hyperemesis and even thyrotoxicosis (hCG stimulates TSH receptors).
"Must Follow Up hCG": After evacuation, hCG must be monitored until normalised and for months afterwards to detect persistent GTD or choriocarcinoma.
"No Oxytocin Before Evacuation": Avoid uterotonics before suction curettage as they may embolise molar tissue.
Incidence
- 1-3 per 1000 pregnancies (UK)
- Higher in Southeast Asia
Risk Factors
| Factor | Notes |
|---|---|
| Age extremes | <16 or >5 years |
| Previous molar pregnancy | 1-2% recurrence |
| Asian ethnicity | Higher incidence |
Types
| Type | Genetics | Fetus | hCG | Malignancy Risk |
|---|---|---|---|---|
| Complete Mole | 46XX (all paternal) | None | Very high | 15-20% |
| Partial Mole | 69XXY (triploid) | Some fetal tissue | Moderately high | 1-5% |
Mechanism
- Complete: Empty ovum (no maternal DNA) fertilised by single sperm that duplicates (46XX) or two sperm (46XY) — purely paternal
- Partial: Normal ovum fertilised by two sperm → Triploid (69 chromosomes)
Why High hCG?
- Abnormally proliferating trophoblast produces excessive hCG
- hCG can cross-react with TSH receptor → Thyrotoxicosis
Symptoms
| Feature | Notes |
|---|---|
| Vaginal bleeding | Most common (90%); often in 1st trimester |
| Hyperemesis gravidarum | Severe nausea/vomiting (high hCG) |
| Uterus large for dates | Complete mole |
| Passage of grape-like vesicles | Pathognomonic if seen |
| Hyperthyroid symptoms | Tremor, tachycardia, sweating |
Less Common
Abdominal
- Uterus large for dates (complete mole)
- May be small or appropriate (partial mole)
Speculum
- Bleeding from os
- Possibly grape-like vesicles
General
- Signs of thyrotoxicosis (tremor, tachycardia)
- Pallor (if significant bleeding)
Laboratory
| Test | Finding |
|---|---|
| hCG | Highly elevated (often >00,000 mIU/mL) |
| FBC | Anaemia (if bleeding) |
| TFTs | Thyrotoxicosis (TSH low, T4 high) |
| Coagulation | Usually normal |
Imaging
| Modality | Findings |
|---|---|
| Transvaginal Ultrasound | "Snowstorm" or "Bunch of grapes" (multiple vesicles); Absent fetal heart (complete); May see abnormal fetus (partial) |
| Chest X-Ray | Pre-evacuation (baseline for metastatic disease) |
Histology
- Confirms diagnosis after evacuation
- Differentiates complete vs partial mole
Management Approach
┌──────────────────────────────────────────────────────────┐
│ MOLAR PREGNANCY MANAGEMENT │
├──────────────────────────────────────────────────────────┤
│ │
│ INITIAL MANAGEMENT: │
│ • Stabilise if bleeding heavily │
│ • Bloods: hCG, FBC, Group & Save, TFTs │
│ • Chest X-Ray (baseline) │
│ │
│ EVACUATION: │
│ • Suction Curettage (ERPC) under GA │
│ • Avoid medical management (risk of embolisation) │
│ • DO NOT give oxytocics before evacuation │
│ • Anti-D if Rh negative │
│ │
│ POST-EVACUATION FOLLOW-UP (CRITICAL): │
│ • Register with GTD Centre (UK: Charing Cross, │
│ Sheffield, Dundee) │
│ • Serial hCG monitoring: │
│ - Weekly until normalised │
│ - Then monthly for 6 months (complete mole) │
│ - Or until normal in partial mole │
│ • Avoid pregnancy until hCG surveillance complete │
│ (6 months after normalisation for complete; │
│ can try after 3 normal values for partial) │
│ │
│ IF hCG RISES OR PLATEAUS: │
│ • Persistent GTD or Choriocarcinoma = CHEMOTHERAPY │
│ • Refer urgently to GTD centre │
│ │
│ CONTRACEPTION: │
│ • Use reliable contraception during follow-up │
│ • Avoid pregnancy until cleared │
│ • (Pregnancy would interfere with hCG monitoring) │
│ │
└──────────────────────────────────────────────────────────┘
Of Molar Pregnancy
- Haemorrhage
- Hyperemesis
- Thyrotoxicosis
- Pre-eclampsia (rare, early)
- Theca lutein cysts
Persistent GTD / Malignancy
- Invasive mole: Mole invades myometrium locally
- Choriocarcinoma: Highly malignant; metastasises early (lung, brain, liver)
- Placental site trophoblastic tumour (PSTT): Rare
Treatment of Persistent GTD
- Chemotherapy (methotrexate for low risk; multi-agent for high risk)
- Cure rate >95% even with metastatic disease
After Evacuation
- 80-85% of complete moles resolve with evacuation alone
- 95-99% of partial moles resolve without further treatment
Persistent GTD
- 15-20% of complete moles require chemotherapy
- 1-5% of partial moles require chemotherapy
- Cure rate with chemotherapy: >95%
Future Pregnancies
- Can have normal pregnancies after hCG normalised
- Recurrence risk: 1-2%
Key Guidelines
- RCOG Green-top Guideline No. 38: Gestational Trophoblastic Disease
- UK GTD Centres (Charing Cross, Sheffield, Dundee)
Key Evidence
Follow-Up
- Centralised follow-up significantly improves outcomes
- UK has one of the best outcomes worldwide
What is a Molar Pregnancy?
A molar pregnancy is an abnormal pregnancy where the placenta grows in an unusual way and a baby doesn't develop normally (or at all). It happens because of a problem at fertilisation.
What Are the Types?
- Complete mole: No baby develops; the placenta forms abnormally
- Partial mole: Some fetal tissue develops, but it's not viable
What Are the Symptoms?
- Vaginal bleeding in early pregnancy
- Severe morning sickness
- Uterus larger than expected for dates
How is It Treated?
The abnormal tissue is removed by a small operation (suction curettage). You will then need regular blood tests and/or urine tests to check your hCG levels go back to normal.
Why is Follow-Up Important?
In a small number of cases, some abnormal tissue remains or grows back, which can become cancerous (choriocarcinoma). The good news is that if caught early, chemotherapy is extremely effective — with cure rates over 95%.
Can I Get Pregnant Again?
Yes, but you should wait until you've been given the all-clear from the specialist centre. Future pregnancies are usually normal.
Primary Guidelines
- Royal College of Obstetricians and Gynaecologists. Green-top Guideline No. 38: Gestational Trophoblastic Disease. 2020. rcog.org.uk
Key Studies
- Seckl MJ, et al. Gestational trophoblastic disease. Lancet. 2010;376(9742):717-729. PMID: 20673583