Although the perspective of hyperemesis gravidarum (HG) has improved over the past decades, there are still several big hurdles in HG research and patient care. For one, the aetiology of HG is poorly understood and tools to diagnose or predict disease severity are lacking. This hampers identification of women at risk for a severe disease course of HG. Secondly, there is an absence of high-quality evidence on the effective treatment of HG. This negatively affects patient care. Third, research assessing possible long-term consequences of HG for the offspring are limited. Therefore, potential harm for the offspring may not be addressed in current clinical practice. Lastly, there is no consensus on the definition of HG, or on outcomes that should be reported in trials. This hampers meaningful aggregation of trial results in meta-analysis and implementation of evidence in guidelines. In this thesis, we address the identified problems.