What causes ‘extreme morning sickness’? What we know, don’t know and suspect about hyperemesis gravidarum

Most women experience some nausea and vomiting in early pregnancy.

Although this is called morning sickness, it can happen at any time of day. Up to 80% of women report nausea and vomiting throughout the day.

While morning sickness is unpleasant and can be incapacitating, milder forms are usually manageable and often get better after the first three months of pregnancy.

But around one in 50 pregnant women (1–3% worldwide) experience morning sickness so extreme they are unable to eat or drink normally or do everyday activities.

This condition, called hyperemesis gravidarum, can last the whole pregnancy and be dangerous for both the woman and the fetus. It is the most common cause of hospitalisation in early pregnancy, but research is still emerging about exactly why it happens.

Here’s what we know, don’t know and suspect.

What causes hyperemesis gravidarum?

Until about five years ago, scientists believed the pregnancy hormone, human chorionic gonadotropin (hCG), was the culprit. But we now know the main cause of all morning sickness – including hyperemesis gravidarum – is high levels of a hormone called GDF15.

A person’s sensitivity to GDF15 depends on how much of this hormone their bodies produce before pregnancy.

Women with naturally low pre-pregnancy levels are more sensitive to the GDF15 the placenta produces during pregnancy, compared to those whose levels were already high before pregnancy. This means having low pre-pregnancy GDF15 levels is a risk factor for developing hyperemesis gravidarum.

However, while there is a blood test that can measure GDF15 levels, it is not currently used to diagnose hyperemesis gravidarum.

The test can be used to investigate some medical conditions associated with high GDF15, including some cancers and some chronic conditions. But high GDF15 levels alone aren’t enough to distinguish hyperemesis gravidarum from other causes of vomiting during pregnancy.

Some other factors that increase the risk of hyperemesis gravidarum include:

• having had this condition in a previous pregnancy
• multiple pregnancy (twins, triplets or more)
• being pregnant for the first time
• a family history of hyperemesis gravidarum
• a history of motion sickness or migraine.

What are the symptoms?

Women with hyperemesis gravidarum can’t stop vomiting and lose a significant amount of weight (more than 5% of their pre-pregnancy weight). As they can’t keep food or fluids down, they can become dangerously dehydrated.

Signs of dehydration include ketonuria (high amounts of acids in the urine, measured in a urine test), very low blood pressure (which can cause dizziness), and imbalances of electrolytes. Electrolytes are crucial for various bodily processes, including nerve and muscle function, and to keep you hydrated.

Because symptoms are so severe, women often need hospital care for periods of time, sometimes repeatedly throughout the pregnancy. Many people may have first heard of the condition via Catherine, Princess of Wales. She made headlines sharing her experiences of hyperemesis gravidarum and her need for frequent medical care.

How is it treated?

There is no cure for hyperemesis gravidarum, so management of the condition focuses on reducing symptoms.

Rehydration

Intravenous fluids can be used for rehydration and to restore electrolyte balance.

Reducing vomiting

While research is inconclusive on the best way to reduce vomiting, there are several anti-nausea drugs that are safe to take in pregnancy. Taking ginger supplements is another safe and effective way to reduce nausea and vomiting.

Nutrition

A dietitian may be able to help by monitoring any nutritional deficiencies and suggesting certain foods or nutritional supplements. However, in very severe cases, where someone’s vomiting doesn’t respond to treatment and can’t be controlled, they may need tube feeding or an intravenous drip to provide all their nutrition.

Mental health

The physical symptoms of hyperemesis gravidarum are debilitating and women who experience it have an increased risk of anxiety and depression. So it’s also essential to monitor mental health and, if needed, offer referrals for psychological support.

The flow-on health effects

Hyperemesis gravidarum is detrimental to the health of both mother and fetus.

Because they can’t eat or drink during pregnancy, women with the condition don’t get enough fluids, calories or nutrients, including vitamins. This causes nutritional deficiencies which can harm their health.

It also increases the risk of severe pregnancy complications including placental abruption (where the placenta suddenly separates from the uterus wall) and pre-eclampsia (which causes high blood pressure and can affect the liver, kidney and brain).

Hyperemesis gravidarum also increases the risk a baby will be born prematurely, with a low birth weight, and/or be admitted to the neonatal intensive care unit.

Hopes for prevention

The finding that low pre-pregnancy GDF15 levels are linked to hyperemesis gravidarum may help us find new ways to treat and prevent it.

For example, researchers are looking at whether blocking how GDF15 works during pregnancy can reduce nausea. Theories about how to prevent the condition focus on boosting GDF15 levels before pregnancy.

These advances give hope for the future. But for now, the best we can do is to improve awareness and understanding about this debilitating condition – including among health professionals – and support women who suffer from it.

Hyperemesis Australia and the Centre Of Perinatal Excellence (COPE) websites are good places to start learning more about hyperemesis gravidarum and how to support women who experience it.