Nausea and vomiting of pregnancy: endocrine basis and contribution to pregnancy outcome.

For a majority of women, nausea and vomiting of pregnancy (NVP) is an unpleasant but normal feature of pregnancy. NVP has a largely unknown etiology, but it is widely agreed that physiological, psychological, genetic, and cultural components are contributing factors. The occurrence of NVP may be of benefit in pregnancy, and NVP-associated pregnancies are less likely to result in miscarriage, preterm delivery, or intrauterine growth retardation. It has been suggested that NVP is promoted by secretion of human chorionic gonadotrophin (hCG), largely on the basis of the coincidence between the onset of NVP and hCG secretion and the peaks of both at around 12 to 14 weeks' gestation. Concentrations of hCG that are above or below the normal range are associated with poor pregnancy outcomes. It seems that NVP and hCG are related and that nutrient restriction during critical periods of embryonic development may ensure production of hCG at optimal levels, protect placental development, and optimize nutrient partitioning between maternal and fetal tissues.