Hyperemesis gravidarum and birth outcomes-a population-based cohort study of 2.2 million births in the Norwegian Birth Registry

Objective: To study associations between hyperemesis gravidarum (HG) and birth outcomes.

Design: Population-based cohort study.

Setting: Norway.

Sample: Singleton births in the Norwegian Birth Registry, 1967-2009 (n = 2 270 363).

Methods: Multiple logistic regression was applied to study associations between HG and dichotomous outcomes; multiple linear regression to study associations between HG, birthweight and gestational length. Generalised estimating equations were applied to obtain valid standard errors. Sub-analysis on data with available information on smoking was conducted (1999-2009).

Main outcome measures: Small and large for gestational age (SGA/LGA), Apgar score after 5 minutes, very preterm and preterm birth (VPTB/PTB), perinatal death, stillbirth, neonatal death, birthweight and gestational length.

Results: No associations between HG and adverse pregnancy outcomes were observed in crude analyses, except for VPTB (odds ratio [OR] 0.79, 95% CI 0.67-0.93). In adjusted analysis, HG was associated with perinatal death (OR 1.27, 95% CI 1.08-1.48). Inverse associations were observed between HG and VPTB (OR 0.80, 95% CI 0.68-0.94) and LGA (OR 0.95, 95% CI 0.90-0.99). Sub-analyses showed no associations between HG and perinatal death (OR 1.29, 95% CI 0.91-1.83). The inverse associations between HG, VPTB and LGA were strengthened (OR 0.66, 95% CI, 0.48-0.91 and OR 0.86, 95% CI 0.79-0.93, respectively). Exposed babies had reduced birthweight and gestational length compared with unexposed, adjusted difference - 21.4 g and - 0.5 days, respectively. Adjustment for smoking slightly strengthened the impact of HG on birthweight.

Conclusions: Inverse associations for HG and VPTB and LGA were observed. HG was associated with slight reductions in birthweight and gestational age.