GDF15 culprit: it is now clear why many pregnant women get sick

Flat stomach, nausea, vomiting: Most women are familiar with the symptoms of so-called morning sickness - around 70 to 80 per cent suffer from it in the first trimester of pregnancy. Two per cent even suffer so much that they can hardly eat for weeks, lose weight and are at risk of dehydration. Doctors refer to this as "hyperemesis gravidum".

An international team of researchers from Cambridge and California has now investigated the causes more closely using a combination of different methods - from blood tests and genetic analyses to animal experiments. And they have found out: Vomiting is triggered by a hormone called GDF15, which is produced by the growing foetus. Depending on how sensitive the expectant mother is to this hormone, she will be more affected by morning sickness. The results of the new study were published on Wednesday in the scientific journal Nature.com.

Two hormone variants, only one triggers nausea

According to Welt.de, earlier studies with anorexics and people undergoing chemotherapy have already shown that the GDF15 hormone is associated with vomiting. In the brain, the hormone docks onto receptors and thus triggers nausea. It was also known that GDF15 is produced in the placenta during pregnancy and then enters the mother's head via the bloodstream. However, it was previously unclear whether the GDF15 hormone actually has an effect on morning sickness.

The research team was also able to distinguish between two GDF15 variants in the mother's blood. One comes from the mother's side of the placenta, one from the baby's side. However, only the hormone produced by the foetus triggers the nausea.

The extent to which the pregnant woman is affected by nausea depends on how much GDF15 the unborn child produces. On the other hand, it also depends on how sensitively the mother reacts to it. The hormone is already produced before pregnancy, albeit in smaller quantities. If the woman already had a rather high GDF15 level, she tolerated the hormone better later in the pregnancy. However, if her body was hardly used to the hormone, it reacted particularly strongly to it during pregnancy.

Hyposensitisation to combat the symptoms

This is precisely where the research team now wants to start with a new treatment method. Lowering the GDF15 level could be one way of treating nausea. Or the other way round: increasing the level before pregnancy. In other words, administering the hormone preventively to women with low GDF15 levels - and thus hyposensitising them in a similar way to an allergy. However, the hormone is still too unexplored, so one of these treatment options is probably still a distant dream of the future.

Another possibility would be to block the receptors in the brain that are responsible for the nausea. This approach is already being researched in anorexia sufferers.

One way or another, the new study offers new opportunities for many women to finally treat the causes rather than just the symptoms of morning sickness. "Now we have a clear idea of what the cause of the problem is and we have a way forward, both for treatment and prevention," says study co-author Stephen O'Rahilly from the University of Cambridge