What's a molar pregnancy - and how common is it?

Analysis: It can be challenging for women to explain this complex pregnancy, while grieving a loss and dealing with a cancer risk

Gestational Trophoblastic Disease (GTD) describes a group of rare pregnancy related disorders which can progress to malignant disease, with molar pregnancy as the most common pre-malignant form. Also known as "Hydatidiform Mole", molar pregenancy describes the overactivity of cells (trophoblasts) in the placenta which swell and produce fluid filled cysts. This abnormal placenta produces very high levels of the pregnancy hormone, human chorionic gonadotrophin (hCG), which is used as a sensitive marker in GTD management and prognosis. Molar pregnancies always end in a miscarriage.

A molar pregnancy occurs in about one in every 600 pregnancies, so we would expect to see approximately 120 molar pregnancies each year in Ireland. Risk factors for molar pregnancy include the woman's age (under 18 and over 40 years of age) which influences egg maturity, and previous history of a molar pregnancy, which raises the woman's risk to about one in 100. However, women can still have a successful pregnancy following a molar pregnancy.

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From Cork University Hospital in 2017, what is a molar pregnancy?

A complete mole develops when a sperm and an "empty" egg form a pregnancy with DNA from the male parent only and no fetal (baby) development. A partial mole develops when two sperm and an egg form a pregnancy with three copies of each chromosome (triploidy) and there can be some fetal development.

The mechanism underlying molar pregnancy is unknown, but is thought to be associated with an imprinting defect. Imprinting describes a phenomenon whereby genes are expressed or silenced depending on whether they are inherited from the mother or father’s DNA. In a molar pregnancy, there is an imbalance in the chromosome number contributed by the father versus the mother.

Women with molar pregnancy often have vaginal bleeding and severe nausea in the first trimester (first 12 weeks) associated with overproduction of the pregnancy hormone (hCG). Ultrasound scans predict the diagnosis of molar pregnancy in 73% of complete moles due to a characteristic "snowstorm" appearance on scanning but only predict 35% of partial moles.

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From RTÉ 2fm's Jennifer Zamparelli Show, clinical midwife and specialist in bereavement and loss, Brenda Casey talks about pregnancy loss

Women are offered surgical management to remove the molar tissue and end the abnormal pregnancy. The diagnosis of molar pregnancy is confirmed following examination of the placental tissue in a pathology laboratory. Rarely, a complete or partial mole may develop alongside a normal fetus in the womb and the normal part of this pregnancy can survive. These complex cases are managed by clinicians with experience in molar and multiple pregnancy.

Following removal of the molar tissue, the woman's blood hCG levels are regularly monitored until they return to normal pre-pregnancy levels. The hCG levels usually normalise within six weeks for a partial mole, but can take longer for a complete mole. Women describe this experience of waiting for their pregnancy hormone levels to drop as like a "rollercoaster." If a woman becomes pregnant during this period, it may mask a rising hCG level which could indicate persistence of abnormal cells (trophoblasts) and progression to cancer.

A National GTD Centre was established in Cork University Maternity Hospital in 2017 and consists of a multidisciplinary team who monitor all molar pregnancies in Ireland. Research has demonstrated that countries with centralised GTD care have better survival rates. National Clinical Guidelines for GTD diagnosis and management were published by the Health Service Executive in 2022.

From RTÉ Radio 1's Morning Ireland in 2019, Trish and Daniel Clifford talk about how the bereavement team at Cork University Maternity Hospital helped them, while Dr Keelin O Donoghue, Leader of the Pregnancy Loss Research Group discusses the implementation of a new set of national standards for bereavement care

A diagnosis of molar pregnancy can be very distressing for women, especially for those approaching the end of their reproductive life. These women have not only lost their much-wanted pregnancy, but now have the added worry of developing a malignancy. The cancer risk is associated with the type of molar pregnancy and complete moles carry a higher risk (15-20%) than partial moles (0.5-1%).

Women who develop malignancy require urgent treatment and have excellent cure rates when managed in expert centres. Most women are treated with single agent chemotherapy for eight-day cycles until hCG levels normalise, which has little to no impact on their ability to have more children. During hCG follow-up monitoring, women often have to pay for GP visits to get a weekly blood test, which is not covered under the maternity and infant care scheme.

Use of molecular genetic techniques to confirm GTD diagnosis has led to more accurate incidence rates and suggests under-reporting of molar pregnancy in Ireland. The success of newer treatments (immunotherapy) for women resistant to chemotherapy has led to cure rates approaching 100%.

From RTÉ Radio 1's Morning Ireland in 2022, Joan O'Sullivan reports on a Labour Party bill to provide paid leave for women who suffer a miscarriage

My research project in the National GTD centre and working with colleagues in the UCC School of Biochemistry & Cell Biology and the Pregnancy Loss Research Group, is seeking to identify blood tests (biomarkers) to predict which women will develop malignancy after molar pregnancy so we can treat them at the earliest opportunity.

Understandably, it can be challenging for women to try to explain this complex pregnancy to family and friends while grieving a pregnancy loss and dealing with a cancer risk. There is a need to raise awareness around molar pregnancy to ensure women get the appropriate emotional and financial support to help them through this difficult time. There is also a knowledge gap in the wider medical and nursing profession around molar pregnancy which needs to be addressed.

Molar pregnancy is a rare condition requiring standardised care and follow-up surveillance by an expert centre or team. Women who experience pregnancy loss should be able to attend dedicated clinics in maternity hospitals, remote from other expectant mothers, so their psychological and bereavement counselling needs can be met.

The views expressed here are those of the author and do not represent or reflect the views of RTÉ. If you have been affected by issues raised in this article, support information is available online

What's a molar pregnancy - and how common is it?

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Caroline Joyce