OBJECTIVE

To study associations between maternal prepregnant body mass index (BMI), smoking, and hyperemesis gravidarum (hyperemesis).

METHODS

The sample consisted of 33,467 primiparous women from the Norwegian Mother and Child Cohort Study (1999-2008). Data on hyperemesis, BMI, education, maternal age, eating disorders, maternal and paternal smoking habits were obtained from questionnaires. All associations were studied by logistic regression.

RESULTS

Altogether, 353 (1.1%) women had hyperemesis. Among non-smokers, both underweight and obese women were more likely to develop hyperemesis than normal-weighted women: odds ratio (OR), 2.36; 95% confidence interval (95% CI), 1.43-3.88 and OR, 1.48; 95% CI, 1.00-2.20, respectively. No associations were found among smokers. Women who smoked daily (OR, 0.44; 95% CI, 0.32-0.60) or occasionally (OR, 0.64; 95% CI, 0.44-0.93) had lower risk of hyperemesis than non-smokers. No effect of partner's smoking habits was observed.

CONCLUSIONS

Both underweight and obesity were associated with hyperemesis, but only among non-smokers. Maternal prepregnant smoking reduced the risk of hyperemesis, whereas partner's smoking habits had no effect.