The aetiology of nausea and vomiting during pregnancy (NVP) is multifactorial, but the relative contribution of biological and psychological determinants is insufficiently understood. We examined the association of human chorionic gonadotropin (hCG), thyroid hormones (thyroid-stimulating hormone and thyroxin) and psychological factors with NVP.

Blood chemistry and psychological measures were obtained in 1682 pregnant women participating in the Holistic Approach to Pregnancy and the first Postpartum Year (HAPPY) study between 12 and 14 weeks of gestation. The presence of NVP was measured using the Pregnancy-Unique Quantification of Emesis scale. Depressive symptoms were assessed using the Edinburgh Depression Scale. Multivariable logistic regression analyses were used to investigate the independent role of hCG, thyroid hormones and depression as related to NVP, adjusting for age, body mass index, education, parity, smoking status, unplanned pregnancy and history of depression.

Elevated levels of NVP were observed in 318 (18.9%) participants. High hCG levels [odds ratio (OR) = 1.47, 95% confidence interval (CI) = 1.11–1.95], elevated depressive symptoms in the first trimester (OR = 1.67, 95% CI = 1.15–2.43) and a history of depression (OR = 1.53, 95% CI = 1.11–2.11) were independently related to high NVP. Multiparity (OR = 1.47, 95% CI = 1.12–1.92) and younger age (OR = 0.91, 95% CI = 0.87–0.94) were also associated with high NVP, whereas (sub)clinical hyperthyroidism was not related to high NVP.

The current study is the first to demonstrate that a combination of hCG hormone and psychological factors are independently related to nausea and vomiting during early pregnancy.