What causes hyperemesis gravidarum?

The causes of hyperemesis gravidarum are poorly understood and likely multifactorial. Genetics appear to play an important role, as risk increases substantially if a sister or mother experienced hyperemesis gravidarum during pregnancy.^[1] In fact, a genome-wide association study found that two genes, GDF15 and IGFBP7, are associated with hyperemesis gravidarum. These genes are involved in the formation of the placenta and appetite regulation.^[2] Hormonal changes during pregnancy, particularly increased human chorionic gonadotropin but also changes in progesterone, estrogen, and thyroid hormones, have been found to be associated with an increased risk of hyperemesis gravidarum in some research. It is speculated that people with hyperemesis gravidarum may have higher than normal levels of these hormones; however, the data are inconsistent, and clear associations between levels of these hormones and risk of hyperemesis gravidarum are lacking.^[3][4][5]