Overview
Clinical Pattern and Mechanism
Nausea and vomiting affect many pregnancies, but hyperemesis gravidarum (HG) is not simply “severe morning sickness.” The Windsor consensus describes HG as symptoms beginning be...
Nausea and vomiting affect many pregnancies, but hyperemesis gravidarum (HG) is not simply “severe morning sickness.” The Windsor consensus describes HG as symptoms beginning before 16 weeks’ gestation, with severe nausea and/or vomiting, inability to eat or drink normally, and severe restriction of ordinary activities. Dehydration and weight loss support the assessment of severity, but neither dehydration nor ketonuria is required for the diagnosis. The current mechanistic model centres on fetoplacental growth differentiation factor 15 (GDF15). GDF15 acts on GFRAL receptors in the maternal area postrema, a vomiting-control region of the brain. Risk depends on both how much GDF15 the fetoplacental unit produces and how sensitive the pregnant patient is to it. A patient with low pre-pregnancy GDF15 may react strongly when pregnancy raises the hormone; chronically high GDF15 exposure may produce tolerance. Genetic differences involving GDF15 and GFRAL help explain familial recurrence. Human chorionic gonadotropin (hCG) may contribute, especially when levels are unusually high in multiple gestation or molar pregnancy, but an hCG explanation alone should not end the assessment. hCG can also weakly stimulate the thyroid. Gestational transient...