Introduction

Molar pregnancy, also called hydatidiform mole or gestational trophoblastic disease,  is an abnormal pregnancy characterised by excessive trophoblastic proliferation. Trophoblasts are cells that are normally present in the placenta.

A molar pregnancy occurs when these placental cells grow in an uncontrolled and irregular manner instead of resulting in a normal embryo, an abnormal mass is formed.

In accordance with the presence or absence of foetal tissue, molar pregnancy can be divided into two types: partial molar pregnancy and complete molar pregnancy.

A hydatidiform mole is a quite rare disease but can have serious consequences on the mother’s health therefore it should be taken seriously with a better understanding of the disease and how to prevent it and detect it early for prompt management.

Understanding molar pregnancy: causes and risk factors

To have a better understanding of a molar pregnancy, let's first dive into normal pregnancy events starting with normal fertilisation.

During normal fertilisation, a sperm containing 23 chromosomes fertilises an ovum containing 23 chromosomes as well, resulting in an embryo which will develop to become a fetus. 

In a molar pregnancy, an abnormal fertilisation occurs:

• In complete molar pregnancy; one or two sperm fertilise an egg with absent or inactivated chromosomes. In this case, there will be 2 sets of paternal chromosomes and none from the maternal side. This will result in an abnormal development of placental tissue.
• In partial moles, on the other hand, a normal egg containing 23 chromosomes will be fertilised by either 2 sperm or one sperm containing duplicated genetic material. This will result in abnormal foetal development and abnormal placental tissue formation.

Hydatidiform mole is an infrequent disorder and here are some of its predisposing factors:¹

• Extremes of maternal age: a maternal age greater than 35 or less than 20 years old can increase the risk of getting a molar pregnancy
• Previous molar pregnancy: a woman who had had a molar pregnancy has a 1-2% risk of having it in her future pregnancies
• Women with a previous history of miscarriage or abortion
• Dietary deficiency: women having a diet deficient in Vit A and animal fat
• Smoking

Incidence rates

Molar pregnancy is not a frequent disorder and has an incidence of 0,2 to 9.9 per 1,000 pregnancies worldwide. With variable incidence rates among different regions, molar pregnancy has a higher incidence rate in Asia compared to most western regions.²

Prevention of molar pregnancy

Although a molar pregnancy can’t be absolutely and completely prevented, a woman who had a previous molar pregnancy can discuss with her healthcare provider possible ways to reduce the risk in the upcoming pregnancies through genetic counselling and screening and by avoiding certain risk factors.

Genetic counselling and screening

Genetic counselling can play an important role in preventing future molar pregnancies by identifying individuals at risk and providing guidance.

Based on personal and family history, genetic counselling helps assess individual risks such as advanced maternal age and previous molar pregnancy.

Counsellors explain inheritance patterns and the risk of recurrence; as well as educate patients about the nature of the disease help individuals make informed decisions and provide emotional support.

Screening of molar pregnancy determines the likelihood of getting it. 

Here are some key methods done to screen for molar pregnancy:

• Preconception screening: it's a screening done for individuals before conception with a high risk of getting a molar pregnancy or those who have had a molar pregnancy. It consists of a specific genetic test called karyotyping to detect chromosomal abnormalities
• Prenatal screening: These are tests done during early pregnancy to determine the presence of molar pregnancy in high-risk individuals. It consists of ultrasound (abdominal or vaginal) and blood or urine tests to quantify the hormone hCG levels

Avoiding risk factors 

As there is no absolute way to prevent a molar pregnancy from developing, individuals can take a proactive step by seeking medical advice, identifying the risk factors and maintaining a healthy lifestyle. 

Those who had a previous molar pregnancy can take a further step by doing genetic counselling to identify any possible chromosomal abnormality.

Early detection methods

Signs and symptoms of molar pregnancy

The hydatidiform mole may present with diverse signs and symptoms, some of which may resemble those of a normal pregnancy. Here are some signs and symptoms of molar pregnancy:³

• Bleeding from the vagina: this may be dark brown to bright red and it's often the first sign of molar pregnancy. Alongside may be grape-like cysts passing with the blood from the vagina
• Severe nausea and vomiting: More intense than in normal pregnancy and may lead to hyperemesis gravidarum
• Pelvic pain and pelvic pressure: this may be due to rapid uterine growth during early pregnancy
• Anaemia: this may be due to a large amount of blood loss
• Elevated blood pressure which may lead to preeclampsia
• Absent foetal movements: later during the second trimester the patient may notice that there are no foetal movements felt although she should be feeling them at that time

Diagnostic tests and procedures

Ultrasound imaging

This includes abdominal or transvaginal ultrasonography. This procedure is done routinely in every pregnancy to confirm an intrauterine pregnancy and exclude any other anomaly.

During this procedure, the healthcare professional either detects a molar pregnancy accidentally or confirms a molar pregnancy from the signs and symptoms of the patient.

There is a characteristic “snowstorm” appearance on the scans of a molar pregnancy and there may be some foetal tissues in a partial hydatidiform mole. However, in a complete hydatidiform mole, no foetal tissue can be detected.⁴

HCG blood and urine tests

Human chorionic gonadotropin is a hormone that is produced normally in the placenta. It helps in foetal development. This hormone is released into the bloodstream and excreted in the urine.

In a molar pregnancy, it is secreted in an excessive amount because of the abnormal placentation. Thus, measuring its levels in blood and urine and comparing it to its normal amounts in normal pregnancy can be used as a diagnostic measure in molar pregnancy.

Management and treatment

After confirming the diagnosis of a molar pregnancy, a healthcare professional should proceed to the treatment of this molar pregnancy.

Treatment of hydatidiform mole might be either surgical or medical:⁵

Surgical treatment

It's done through procedures called dilatation and curettage named D&C  or dilatation and suction evacuation named D&E usually done under general anaesthesia. In D&C, a healthcare professional uses a curette, which is a surgical instrument to scrape away the molar tissue. 

During a D&E procedure, the healthcare professional gradually sucks out the molar tissue from the uterus using a thin tube.

Medical treatment

In some cases, a drug can be used to induce uterine contractions which will help expel the content of the uterus.

The surgeon should however decide which treatment is best for the patient.

Follow-up care and monitoring

Following surgical or medical treatment of molar pregnancy, the patient will need a follow-up to ensure complete resolution of the hydatidiform mole. 

It is done through surveillance of hCG levels in blood and urine until it becomes undetectable.

Pelvic physical exams and ultrasonography are also done to ensure that there is no molar tissue left.

FAQs

How much time does it take to recover from a molar pregnancy?

Being fully recovered means that there are no longer detectable levels of hCG in the blood and urine of the patient. Normally, it takes up to 8 weeks to completely recover and follow-up may sometimes take up to 6 months in some patients.⁶

What can happen if a molar pregnancy is left untreated?

Molar pregnancy is usually diagnosed early during routine prenatal examinations and due to its obvious presentations. But if left untreated for a long time it can cause several complications such as a “large for date” uterus,  an overactive thyroid gland and severely elevated blood pressure which may lead to preeclampsia.⁷

Can molar pregnancy turn into cancer?

Yes, the hydatidiform mole can sometimes grow into a cancer called gestational trophoblastic neoplasia. If this occurs, the treatment will be invasive and can include chemotherapy, radiotherapy and removal of the whole uterus.⁸

Having a molar pregnancy can impact future pregnancies and fertility

No, having a molar pregnancy does not have an impact on future pregnancies or fertility, it does slightly increase your risk of getting another molar pregnancy.

Summary

To summarise, molar pregnancy is an infrequent condition. It can be treated but there is no absolute way to prevent its occurrence.

Raising awareness and early prevention of molar pregnancy plays an important role in maternal health and the success of treatment.

As molar pregnancy can be considered like “losing a baby”, this condition can affect patients psychologically and therefore, psychological support plays a vital role in improving outcomes of the patient holistically.