Placenta-associated adverse pregnancy outcomes in women experiencing mild or severe hyperemesis gravidarum – a systematic review and meta-analysis

Background Nausea and vomiting in pregnancy (NVP) affects 50-80% of pregnant women and is correlated to the level of human chorionic gonadotropin (hCG). Hyperemesis gravidarum (HG) is a severe condition, with an incidence of 0.2-1.5%, characterized by consistent nausea, vomiting, weight loss and dehydration continuing after the second trimester. Aim The aim of this systematic review was to investigate a potential correlation between NVP or HG with adverse pregnancy outcomes and hCG levels. Method A systematic search in PubMed, Embase and CINAHL Complete was conducted. Studies on pregnant women with nausea in the first or second trimester, reporting either pregnancy outcomes or levels of hCG were included. The primary outcomes were preterm delivery (PTD), preeclampsia, miscarriage, and fetal growth restriction. Risk of bias was assessed using ROBINS-I. The overall certainty of evidence was assessed using GRADE. Results The search resulted in 2023 potentially relevant studies; 23 were included. The evidence was uncertain for all outcomes, however women with HG had a tendency to have an increased risk for preeclampsia [odds ratio (OR) 1.18, 95% confidence of interval (CI) 1.03 to 1.35], PTD [OR 1.35, 95% CI 1.13 to 1.61], small for gestational age (SGA) [OR 1.24, 95% CI 1.13 to 1.35], and low birth weight (LBW) [OR 1.35, 95% CI 1.26 to 1.44]. Further, a higher foetal female/male ratio was observed [OR 1.36, 95% CI 1.15 to 1.60]. Meta-analyses were not performed for women with NVP; however, most of these studies indicated that women with NVP have a lower risk for PTD and LBW and a higher risk for SGA, and a higher fetal female/male ratio. Conclusion There may be an increased risk in women with HG and a decreased risk in women with NVP for adverse placenta-associated pregnancy outcomes, however the evidence is very uncertain. PROSPERO: CRD42021281218