The medications used for hyperemesis gravidarum do cross the placenta, but they are considered compatible with pregnancy. In general, the medications most commonly used for hyperemesis gravidarum have not been found to be associated with fetal defects, stillbirth, spontaneous abortion, or preterm birth.[1][2]
Compatibility with pregnancy does not mean these medications are risk-free; rather, it means they are generally considered to be safe for the fetus. All medications carry potential risks, and these risks must be weighed against the benefits. In hyperemesis gravidarum, the risks associated with lack of treatment (e.g., dehydration, malnutrition, psychosocial factors, preterm birth, impaired fetal growth) will generally outweigh any risks associated with treatment.[3] Concerns have been raised about the risk of fetal defects following the use of ondansetron during pregnancy. Some research suggests an increased risk of fetal defects, but these studies are controversial since they are of poor methodological and ethical quality.[1] In recent years, multiple large-scale studies have not found an association between ondansetron use during pregnancy and fetal defects. Instead, associations with a reduced risk of miscarriage have been identified.[1][4][5]