How morning sickness develops

More than half of all women suffer from morning sickness and nausea during pregnancy. Until now, it has not been possible to find out exactly what causes this. Researchers measure the level of a certain hormone in the blood, compare it and come up with plausible answers.

An international research team has discovered how widespread morning sickness occurs and why not every woman is affected. The researchers led by Marlena Fejzo from the University of Southern California in Los Angeles analyzed the data of 300 pregnant women who came from different hospitals and were in their first trimester. Particular emphasis was placed on comparing the values of the so-called protein hormone GDF15 (growth differentiation factor 15).

Earlier studies have already provided evidence that there is a connection between the messenger substance and the typical pregnancy nausea, which in the worst case can lead to life-threatening conditions for the expectant mother and the unborn child. This is technically known as hyperemesis gravidarum, or HG for short.

GDF15 is produced in small quantities in all tissues of the human body. The concentration increases measurably during pregnancy. It is conceivable that GDF15 acts on the brain stem and therefore causes nausea and vomiting. In a previously unexamined publication in the journal "Nature", the researchers provide an initial explanation for the complex mechanism that leads to morning sickness.

Blood and genes looked at

As a first step in the study, the GDF concentration in the blood plasma was determined and the pregnant women were asked how they felt. Because GDF15 production in the body depends on a specific gene, the genes of the pregnant women were also sequenced and compared.

The analysis of the data showed that pregnant women with higher GDF15 levels in their blood suffered more frequently from nausea and vomiting than pregnant women with lower GDF15 levels. Through extensive blood tests, the team also clarified that the majority of this hormone is produced by the fetus and released into the mother's body. But why do some women never feel nauseous at any point during their pregnancy?

The researchers also provide a well-founded answer to this question. By comparing GDF15 levels before and during pregnancy, it becomes clear that those who had low levels of GDF15 in their blood before pregnancy often suffered more from nausea and nausea during pregnancy than those who already had high GDF15 levels before pregnancy. For the first group of women, the risk of developing HG also increased. However, those whose GDF15 gene has a rare mutation have an even higher risk, writes the research team.

But there are exceptions: If the unborn child has inherited the mutation on the GDF15 gene, then again there is no or only the usual morning sickness. In this case, the foetus produces less GDF15 so that the concentration of the hormone in the expectant mother's blood changes only slightly or not at all. Accordingly, it has little or no effect on the well-being of the pregnant woman.

High GDF15 levels are not the cause

The data also show that women who already had high GDF15 levels in their blood before pregnancy were less likely to suffer from morning sickness and the risk of developing HG also decreased. This mechanism was particularly pronounced in women suffering from a hereditary blood disorder known as beta-thalassemia.

In summary, the researchers conclude from their results that it is not the absolute GDF15 concentration in the blood of pregnant women that is associated with morning sickness, but the change in GDF15 levels during pregnancy. "We now know that women get sick during pregnancy when they are exposed to higher levels of the hormone GDF15 than they are used to," Fejzo is quoted as saying in a statement from the University of Southern California. This approach also explains why not every woman suffers from nausea and vomiting to the same extent. "Women who are more sensitive to the hormone also suffer more intensely," says Stephen O'Rahilly from Cambridge University, who led the collaboration. "This knowledge gives us a clue as to how we can prevent this," O'Rahilly is further quoted as saying.

"Now that we understand the main cause of HG, we are hopefully one step closer to developing effective treatments. This is the only way to prevent other mothers from experiencing what I and many other women have experienced," concludes Fejzo. It is conceivable that both the administration of small amounts of the messenger substance before pregnancy and the reduction of GDF15 through medication during pregnancy could alleviate the symptoms. But until then, a series of further investigations are necessary.