A molar pregnancy — a hydatidiform mole — means the cells that should have formed the placenta have grown abnormally, and the pregnancy cannot become a baby. That is a real loss, and it usually arrives with a second, frightening sentence about cancer. So here is that part first: most women need one procedure and a run of blood tests, and nothing more. Chemotherapy follows about 13–16% of complete moles and 0.5–1.0% of partial moles, and for those women the UK cure rate is 98–100% (RCOG, 2020). If you are simply bleeding early on, the likelier explanations are ordinary — see early pregnancy bleeding and miscarriage.
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Call 999 or go to A&E or your Early Pregnancy Unit now if you have heavy bleeding (soaking through a pad an hour or passing large clots), severe or one-sided tummy pain, pain at the tip of your shoulder, or you feel faint or very unwell — these can be signs of an ectopic pregnancy or another emergency. Ring your maternity unit, early pregnancy unit or GP the same day for any bleeding or dark discharge, sickness you cannot keep on top of, or tissue passed that contains small grape-like cysts. A private scan appointment is not the right route for any of that, and if a molar pregnancy is already suspected it is your NHS early pregnancy unit and the national screening service — not us — who need to see you.
A baby normally receives one set of chromosomes from the egg and one from the sperm. In a molar pregnancy that balance is wrong from the first cell division, and the tissue that should have become the placenta overgrows into clusters of small fluid-filled sacs — the appearance behind the old name, hydatidiform mole. It is decided at fertilisation. Nothing about your diet, work, sex, exercise, stress, contraception, IVF or a previous miscarriage is the cause.
It is uncommon: around 1 in 600 pregnancies in the UK (Cancer Research UK; Miscarriage Association), and the RCOG puts gestational trophoblastic disease at a calculated 1 in 714 live births. Across Western countries complete moles occur in roughly 1 in every 1,000 to 2,000 pregnancies and partial moles in about 3 per 1,000 (Medicina, 2025). Rare enough that an average consultant obstetrician sees perhaps one new case every two years — which is why every UK case goes to a specialist centre.
There are two forms. The difference is genetic, and it decides how likely you are to need further treatment and how long your follow-up runs.
Every chromosome comes from the father. In 75–80% of cases one sperm fertilised an egg carrying no chromosomes of its own and then duplicated its genetic material; in the rest, two sperm fertilised that empty egg (RCOG, 2020). No fetal tissue forms at any stage. Complete moles produce more hCG, cause more symptoms, and carry the higher risk of needing chemotherapy afterwards: 13–16%.
About 90% are triploid — 69 chromosomes rather than 46, two sets from the father and one from the mother, almost always because two sperm fertilised a normal egg (RCOG, 2020). There is usually some fetal tissue, occasionally a heartbeat, but the pregnancy cannot survive. Symptoms are milder, and 0.5–1.0% need chemotherapy afterwards.
Not by ultrasound, and not by an hCG level. They are separated under the microscope after the tissue is removed, using the chromosome count and staining for p57 — a gene expressed only from the mother's copy, so absent in a complete mole.
Very rarely a normal twin develops beside a complete mole. In a large UK series pre-eclampsia occurred in 4% with no maternal deaths, and among women who gave birth after 26 weeks the need for chemotherapy afterwards was 15% — no higher than after a complete mole on its own (RCOG, 2020). Continuing is sometimes possible, but that decision belongs with a fetal medicine unit and a trophoblastic disease centre, not a second opinion scan.
The commonest sign is irregular vaginal bleeding, present in around 60% of cases (RCOG, 2020) — and also in a great many ordinary early pregnancies and in miscarriage, so bleeding alone is not a reason to assume this. One sign is more specific: tissue passed containing small, grape-like fluid-filled cysts (Miscarriage Association). Keep it and tell your early pregnancy unit.
Less often a mole shows itself through the effects of very high hCG — sickness that will not settle, a uterus measuring larger than your dates, an overactive thyroid, or pre-eclampsia before 20 weeks. In a complete mole hCG is frequently above 100,000 mIU/mL (Medicina, 2025). But hCG spans a huge normal range, and severe sickness usually means nothing more than severe sickness.
Increasingly there are no symptoms at all. With early scanning now routine, the proportion of women whose only presenting feature was an abnormal ultrasound rose from 1% to 12% between 1996 and 2006, and the average gestation at diagnosis fell from about 16 weeks in the 1960s and 70s to around 9 weeks by 2013 (RCOG, 2020). Most are now found at a scan done for bleeding or reassurance — see early pregnancy bleeding scan and viability scan.
This is the part most people are told imprecisely. A scan can suspect a molar pregnancy. It cannot confirm one, and it cannot reliably exclude one.
After 8 weeks a complete mole typically shows thickened, cystic placental tissue with no gestational sac — the classic snowstorm appearance. A partial mole is subtler: an enlarged placenta with cystic spaces beside an empty or small sac. Routine pre-evacuation ultrasound identified 35–40% of moles before 14 weeks and about 60% after; sensitivity is around 95% for complete moles but only 20% for partial ones (RCOG, 2020). A normal-looking scan does not rule this out.
A very high hCG supports the suspicion, but the level varies enormously between healthy pregnancies. The definitive diagnosis is made by examining the tissue under the microscope after the pregnancy is removed (RCOG, 2020) — which is why a firm answer comes weeks after the scan. When tissue is routinely examined after surgical management of miscarriage, 2.7% turns out to be molar or an atypical placental site nodule that nobody had suspected beforehand.
We perform detailed early scans and refer you the same day if the appearance is worrying. We are not a trophoblastic disease centre, we cannot provide histology, and a private scan does not change the course of a molar pregnancy that has already happened. Your NHS early pregnancy unit and the national screening service are the pathway — see private maternity care.
Suction curettage is the method of choice, whatever the size of the uterus, and it is usually a day case under general anaesthetic. In a review of 4,247 women with gestational trophoblastic disease, the risk of later needing chemotherapy was 16-fold higher after medical rather than surgical removal (RCOG, 2020).
Everything removed goes to histopathology, which confirms whether it was a molar pregnancy and whether it was complete or partial. How long that takes varies between hospitals — usually a matter of weeks, and your team can tell you when to expect it.
Your hospital registers you with one of three UK screening centres: Ninewells Hospital in Dundee for Scotland, Weston Park Hospital in Sheffield for northern England and central and north Wales, and Charing Cross Hospital in London for everywhere else. You do not arrange this yourself.
The centre sends pre-paid kits. Urine samples go back in the post; blood is usually taken at your GP surgery or local hospital and forwarded by their laboratory, so you should not have to arrange that yourself. For a complete mole, if hCG normalises within 56 days of the evacuation, follow-up runs 6 months from the procedure; if longer, 6 months from normalisation. For a partial mole it ends once hCG is normal on two samples at least four weeks apart.
If hCG falls and stays down you are discharged, and that is the end of it. If it plateaus or rises, the centre brings you in for assessment and, if needed, treatment.
Britain runs a single national service for this. NHS England's specification designates three centres to register and monitor every case, with a cure rate of at least 98% as the stated objective, and the RCOG treats registration as a minimum standard of care. Nobody is asking you to spot a problem yourself.
A molar pregnancy is not cancer. A minority become a condition called gestational trophoblastic neoplasia (GTN), which is treated as one — and treated extremely successfully.
Chemotherapy follows 13–16% of complete molar pregnancies and 0.5–1.0% of partial ones (RCOG, 2020). Put the other way round: roughly six in seven women with a complete mole, and about 99 in 100 with a partial mole, need nothing beyond the evacuation and the blood tests.
hCG does not fall as it should, or begins to rise again, after the pregnancy has been removed — a sign that some abnormal tissue is still active. That is what the follow-up looks for, and why tests continue once you feel physically well.
Treatment is decided by the FIGO score. Women scored low risk have a single drug, usually methotrexate, as an outpatient; those scored high risk have a multi-drug regimen in hospital (RCOG, 2020). The RCOG describes the overall cure rate as close to 100%. About 80% go on to have further pregnancies afterwards.
The RCOG's advice is to wait until your hCG follow-up is complete. The reason is mechanical rather than cautious: a new pregnancy raises hCG and hides the exact signal the follow-up depends on. After a partial mole that can be weeks; after a complete mole where hCG normalised within 56 days, 6 months from the procedure; a year if chemotherapy was needed. Among 241 UK patients who did conceive within 12 months of chemotherapy there was no significant increase in miscarriage, ectopic pregnancy, a further mole or stillbirth (RCOG, 2020).
The risk of a second molar pregnancy is about 1%. If you have had more than one loss, our recurrent miscarriage page covers the separate investigations worth doing. Next time, an early scan — see early fetal scan and 10 week scan — can confirm the pregnancy is developing and can raise the suspicion of a mole. It cannot rule one out, and it cannot alter the course of one already begun.
No. It is an abnormally growing placenta, not a cancer. A minority become gestational trophoblastic neoplasia, which is treated with chemotherapy: that follows 13–16% of complete moles and 0.5–1.0% of partial ones, and even then the UK cure rate is 98–100% (RCOG, 2020).
No. A molar pregnancy is decided at fertilisation — by an egg carrying no chromosomes of its own, or by two sperm reaching one egg. It is not caused by anything you ate, drank, lifted or worried about, nor by a previous termination, contraception or IVF.
With a complete mole, no fetal tissue forms at any point: there was a pregnancy, with a positive test and real symptoms, but never a baby. With a partial mole there is usually some fetal tissue and occasionally a heartbeat, but it cannot survive. This is a bereavement either way.
About 1 in 600 pregnancies (Cancer Research UK; Miscarriage Association); the RCOG's figure for gestational trophoblastic disease overall is 1 in 714 live births. It is commoner at the extremes of age — around 1 in 500 pregnancies under 15, and 1 in 8 over 50.
Sometimes, and less often than people assume. Routine pre-evacuation ultrasound identifies 35–40% of molar pregnancies before 14 weeks and about 60% after (RCOG, 2020); most are reported on the day as a missed miscarriage. A scan raises the suspicion — only the tissue confirms it.
Irregular vaginal bleeding is the most common, in around 60% of cases. Less often: sickness that will not settle, a uterus larger than your dates, an overactive thyroid, or pre-eclampsia before 20 weeks. Passing tissue with small grape-like cysts is the most specific sign — the others all happen in ordinary pregnancies too.
Because hCG is the only reliable way to tell whether abnormal tissue is still active. For a complete mole where hCG normalises within 56 days of the evacuation, follow-up runs 6 months from the procedure; if longer, 6 months from the date it normalised. For a partial mole it ends once two samples four weeks apart are normal.
Until your hCG follow-up is complete, because a new pregnancy raises hCG and hides the signal it relies on. In practice: weeks after a partial mole, around 6 months after a complete mole, and a year if chemotherapy was needed. Ask your screening centre for your own date.
Almost certainly not. The risk of a further molar pregnancy is about 1% — roughly 1 in 100 — slightly higher after a complete than a partial mole (RCOG, 2020). A separate figure sometimes quoted alongside it is 1 in 4,011: that is how rarely trophoblastic disease turned up on routine hCG screening after a later pregnancy in women who had not needed chemotherapy — so rarely that the RCOG no longer asks those women to send a sample after each subsequent pregnancy.
For the large majority of women, yes. Among those who needed chemotherapy for GTN, about 80% go on to have further pregnancies, and the chance of conceiving is around 83% after either single-agent or multi-agent treatment. Combination chemotherapy brings menopause forward for some — 13% by age 40 and 36% by 45 (RCOG, 2020).
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The figures and clinical statements on this page are drawn from the sources below. Guidance evolves — always discuss your individual circumstances with a clinician.
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