Hearing the words molar pregnancy can feel like the ground shifts. One day there is a positive test, the next there may be bleeding, intense nausea, and an ultrasound that raises new questions. Parents often think: “Did I do something wrong?”, “Will this affect my chances next time?”, “Why do I need blood tests again and again?” With a molar pregnancy, the focus is clear treatment plus disciplined follow-up—because the abnormal placental tissue can, in a small number of cases, persist.

Understanding molar pregnancy and what it means

What a molar pregnancy is (hydatidiform mole)

A molar pregnancy (also called a hydatidiform mole) is an abnormal pregnancy caused by an error at fertilisation. Instead of forming a normal placenta (and a baby), trophoblast cells—the cells that should build the placenta—grow in an uncontrolled way. You may hear doctors call it trophoblastic disease, because it starts from trophoblastic tissue.

In a molar pregnancy, the placental villi often swell with fluid (hydropic villi) and can resemble many tiny cyst-like vesicles. Most molar pregnancies are not cancer. Even so, some molar tissue can keep growing after removal, which is why careful hormone monitoring is part of standard care.

Why the pregnancy is not viable

The placenta is not just “support tissue”. It is the organ handling oxygen, nutrient transfer, and hormone production. When placental development is disorganised from the start, the pregnancy cannot progress normally.

• Complete mole: no embryo develops.
• Partial mole: an embryo may be seen, but it has a major chromosomal abnormality and is not viable.

A pregnancy test is positive because this trophoblastic tissue produces hCG, often in high amounts.

Molar pregnancy vs miscarriage, ectopic pregnancy, and blighted ovum

Early pregnancy problems can look similar at first—spotting, cramps, a positive test—yet the cause and follow-up differ.

• Miscarriage: the pregnancy stops developing, often due to chromosomal issues, hCG usually stops rising and then falls.
• Blighted ovum (anembryonic pregnancy): a sac forms, but no embryo develops.
• Ectopic pregnancy: implantation outside the uterus (often the fallopian tube), can become an emergency.
• Molar pregnancy: abnormal placental growth, hCG may be higher than expected, ultrasound may show a typical “molar” pattern.

People sometimes say “a molar pregnancy is like a miscarriage.” What they usually mean is that the pregnancy is not viable and needs evacuation. The difference is follow-up: a molar pregnancy needs structured surveillance to confirm all abnormal tissue is gone.

How molar pregnancy fits within gestational trophoblastic disease (GTD)

A molar pregnancy is part of gestational trophoblastic disease (GTD).

• Hydatidiform moles (complete and partial) are considered premalignant.
• If tissue persists or spreads, it can become gestational trophoblastic neoplasia (GTN), including invasive mole and, more rarely, choriocarcinoma.

The reassuring point: GTD/GTN are among the most treatable pregnancy-related conditions when follow-up is completed.

Types of molar pregnancy and key differences

Complete molar pregnancy: what happens

A complete mole forms when there is no normal embryo development at all. The uterus contains only abnormal placental tissue.

Key characteristics

• No embryo or normal fetal tissue.
• Villi become swollen and form multiple cystic spaces.

Genetics and mechanism

Most complete moles are androgenetic diploidy—often 46,XX (sometimes 46,XY). Typically, an “empty” egg (no maternal nuclear DNA) is fertilised by one sperm that duplicates its chromosomes, or by two sperm.

Typical hCG levels and symptoms

Because trophoblastic tissue is highly active, hCG can be markedly elevated.

Common symptoms:

• First-trimester bleeding (sometimes dark brown)
• Severe nausea/vomiting (sometimes hyperemesis gravidarum)
• Uterus measuring larger than expected
• Pelvic heaviness or pressure

Very high hCG can also cause:

• Thyroid-like symptoms (palpitations, heat intolerance, tremor)
• Theca-lutein cysts (ovarian cysts driven by hormonal stimulation)

Ultrasound appearance

A complete mole may show the classic “snowstorm appearance” or “cluster of grapes”—an echogenic mass with multiple cystic spaces and no visible fetus.

Partial molar pregnancy: what happens

A partial mole happens when abnormal placental tissue grows alongside abnormal fetal tissue.

Key characteristics

• Fetal tissue or parts may be present.
• The fetus is not viable due to abnormal genetics.

Genetics and mechanism

Most partial moles are triploidy with 69 chromosomes, often 69,XXX, 69,XXY, or 69,XYY, typically due to two sperm fertilising one egg.

Typical hCG levels and symptoms

hCG is elevated but usually not as high as in complete moles.

Symptoms may resemble a missed miscarriage:

• Vaginal bleeding
• Mild to moderate nausea
• Uterus not enlarged

Ultrasound appearance

Ultrasound may show an abnormal cystic placenta and sometimes fetal parts. The picture can be less classic than a complete mole, so confirmation by pathology after evacuation is often needed.

Complete vs partial: risk of persistent disease

Complete moles carry a higher risk of persistent GTD/GTN than partial moles.

Figures often quoted:

• After complete mole: ~10–15%
• After partial mole: ~0.5–3%

These differences can influence how long hCG monitoring is continued.

How common molar pregnancy is

Incidence and why rates vary

A molar pregnancy is uncommon. Rates vary by region and detection practices.

Reported estimates include:

• Europe: ~1 in 1,000
• USA: ~1 in 2,000
• Some parts of Southeast Asia: higher reported rates

Differences may reflect how early ultrasounds are done and how routinely tissue is sent for pathology.

Recurrence risk in a future pregnancy

After one molar pregnancy, recurrence risk is higher than average but still low—often around 1–2%. This is why early ultrasound is commonly offered next time.

Causes and risk factors

How a molar pregnancy forms

A molar pregnancy results from an error during fertilisation and early cell division. It is not caused by food, travel, stress, lifting, or intercourse.

Why genetics matter (genomic imprinting)

Pregnancy tissues rely on balanced genetic contribution and “imprinting” signals from both parents. When that balance is disrupted, placental growth can dominate and embryo development fails.

Risk factors

Better-established factors:

• Very young maternal age (extremes)
• Advanced maternal age
• Prior molar pregnancy

Nutritional links (like low folate or low carotene intake) have been explored in some populations, but they cannot reliably predict who will develop a mole.

Rare genetic predisposition

Rarely, recurrent moles can be linked to inherited variants affecting egg imprinting (e.g., NLRP7, KHDC3L). If there is a history of multiple moles, genetic counselling may be offered.

Symptoms and warning signs

Sometimes there are no clear symptoms

Some cases are detected on early ultrasound before symptoms are prominent.

Common symptoms

Often in the first trimester:

• Vaginal bleeding (brown spotting or heavier bleeding)
• Passing clots (not always)
• Pelvic pain/cramping
• Pelvic pressure/heaviness
• Nausea that feels unusually intense

Signs linked to very high hCG

Very high hCG can overstimulate the body:

• Severe vomiting
• Thyroid-like symptoms (fast heartbeat, sweating, tremor, anxiety, heat intolerance)

Preeclampsia before 20 weeks

Preeclampsia is typically later in pregnancy. When high blood pressure and protein in urine appear before 20 weeks, complete molar pregnancy is one of the red flags clinicians consider.

When to seek urgent care

Seek urgent evaluation for:

• Heavy bleeding (soaking a pad in an hour), dizziness, fainting
• Severe or worsening abdominal/pelvic pain
• Fever, chills, foul-smelling discharge
• Shortness of breath, chest pain, coughing blood
• Severe headache, vision changes, confusion

How molar pregnancy is diagnosed

Clinical assessment

Clinicians consider symptoms, uterine size vs dates, and overall stability (pulse, blood pressure).

Quantitative beta-hCG

Blood beta-hCG helps clarify the picture:

• Levels may be much higher than expected (especially complete mole)
• After treatment, levels should fall to undetectable

Ultrasound

• Complete mole: diffuse abnormal tissue with cystic spaces, often no fetus.
• Partial mole: abnormal placenta ± fetal parts, can overlap with miscarriage.

Confirmation after evacuation (pathology)

Diagnosis is confirmed on histopathology:

• Complete mole: diffuse hydropic villi, marked trophoblastic proliferation, no fetal tissue, typically p57 negative
• Partial mole: focal changes, may include fetal tissue, typically p57 positive, triploidy common

Additional tests

Depending on symptoms:

• CBC
• Blood type and Rh
• Thyroid function tests

Treatment options for molar pregnancy

Initial management

Care focuses on safety:

• Managing bleeding and checking haemoglobin
• Treating dehydration and vomiting
• Addressing thyroid overstimulation if present

Uterine evacuation (suction D&C)

Why it is preferred

First-line treatment is suction evacuation (suction D&C), typically under anaesthesia, sometimes with ultrasound guidance. It removes abnormal tissue and allows tissue to be sent for pathology.

Possible complications

Uncommon, but can include:

• Heavy bleeding
• Infection
• Uterine perforation
• Retained tissue requiring repeat evacuation

Recovery and what starts right away

After the procedure:

• Bleeding and cramping may last days to a couple of weeks
• Clear “when to call” instructions are given
• Beta-hCG follow-up begins soon, because the trend confirms clearance

Hysterectomy in selected situations

A hysterectomy may be considered if future pregnancy is not desired, or if there is significant bleeding. Even then, hCG monitoring is still needed.

Other care around treatment

• Rh(D) immune globulin if Rh-negative
• Histopathology (and sometimes genetic testing)

Follow-up after molar pregnancy (hCG monitoring)

Why follow-up matters

Follow-up is the safety net. Persistent tissue can continue to produce hCG and may invade the uterine wall or spread. Early detection leads to excellent outcomes.

How beta-hCG monitoring usually works

Protocols vary, but commonly:

• Weekly beta-hCG until undetectable
• Then monthly monitoring for a set period

Monitoring is often longer after a complete mole (often around 6 months after hCG normalises) and may be shorter after partial mole depending on protocol.

Signs of persistent disease

Patterns that raise concern:

• hCG plateaus
• hCG rises
• hCG remains positive beyond the expected timeframe

Contraception during surveillance

Why contraception is advised

A new pregnancy makes hCG rise again and can mask persistent disease. Temporary contraception avoids confusion.

Options

Depending on your health and preference:

• Pills
• Condoms
• Implant
• IUD (some teams wait until uterine healing)

Persistent disease, GTN, and treatment if needed

Persistent GTD

Persistent GTD means tissue remains after evacuation, usually detected through hCG trends.

GTN

GTN is diagnosed using hCG criteria and sometimes imaging.

Treatment (highly effective)

Treatment depends on risk scoring:

• Low-risk: single-agent chemotherapy such as methotrexate
• High-risk: multi-agent regimens such as EMA/CO in specialist centres

Future fertility and pregnancy after molar pregnancy

Can you get pregnant again?

Yes. Most parents have healthy pregnancies after a molar pregnancy once treatment and follow-up are complete.

When it may be safe to try again

Many teams advise waiting until hCG is undetectable and surveillance is complete. If chemotherapy was needed, the waiting period is often longer. Your specialist will guide this.

What changes next time

Early ultrasound is usually offered for reassurance, and some teams may check hCG after delivery.

Living with and recovering from a molar pregnancy

Physical recovery

It is common to have light to moderate bleeding, cramps, and fatigue. Follow your clinician’s advice on resuming sex, tampons, exercise, and work.

Emotional recovery

A molar pregnancy can carry grief plus uncertainty because follow-up keeps going. Clear information helps: expected monitoring duration, what “clearance” means, and warning symptoms.

If anxiety or sadness feels persistent, mental health support can make the waiting period easier.

À retenir

• A molar pregnancy is an abnormal fertilisation where placental tissue grows in an uncontrolled way, the pregnancy is not viable.
• Two main types exist: complete (no embryo) and partial (often triploidy).
• Diagnosis uses ultrasound and beta-hCG, confirmed by pathology (often with p57 testing).
• Treatment is usually suction D&C followed by structured hCG monitoring.
• Contraception during follow-up avoids confusion with hCG interpretation.
• Persistent GTD/GTN is highly treatable, often with excellent cure rates.
• Professionals can support you through follow-up and future pregnancy planning, and you can also download the Heloa app for personalised guidance and free child health questionnaires for children.

Further reading:

• Molar pregnancy – Symptoms and causes: https://www.mayoclinic.org/diseases-conditions/molar-pregnancy/symptoms-causes/syc-20375175
• Hydatidiform Mole – StatPearls – NCBI Bookshelf: https://www.ncbi.nlm.nih.gov/books/NBK459155/