Hyperemesis gravidarum (HG)-severe nausea and vomiting during pregnancy-affects 1-3% of pregnancies and is the leading cause of early pregnancy hospitalization. Significant maternal undernutrition in HG pregnancy is hypothesized to lead to abnormal placental development and function, resulting in higher risk for select adverse pregnancy outcomes (APOs). Population data investigating this association are largely from Europe; the only prior US population-based study (1999) did not adjust for confounding. We evaluated the association between HG and APOs in a US population-based cohort of 2.5 million singleton live births in California (2007-2011). We defined HG based on primary diagnosis codes present in prenatal hospitalization or emergency department records (n = 53 681; 2.2%). After adjusting for confounders, HG was associated with higher risks of preeclampsia (aRR 1.18, 95% CI 1.13-1.23), gestational hypertension (1.15, 1.09-1.22), preterm birth (1.25, 1.22-1.29), small for gestational age (1.19, 1.16-1.22), placental abruption (1.14, 1.05-1.25), and anemia (1.37, 1.33-1.40). Risks were generally higher among women with first HG hospitalization in the second trimester (eg, preeclampsia: 1.41, 1.30-1.52), and elevated risks were observed across nearly all strata examined. In this large US population-based cohort, HG was associated with increased risk of multiple APOs.
Keywords: adverse pregnancy outcomes; hyperemesis gravidarum; hypertensive disorders of pregnancy; nausea and vomiting in pregnancy.
© The Author(s) 2026. Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health. All rights reserved.