Anne Matthews, David M Haas, Dónal P O'Mathúna, Therese Dowswell

Nausea, retching and vomiting are very commonly experienced by women in early pregnancy. There are considerable physical, social and psychological effects on women who experience these symptoms. This is an update of a review of interventions for nausea and vomiting in early pregnancy last published in 2014. To assess the effectiveness and safety of all interventions for nausea, vomiting and retching in early pregnancy, up to 20 weeks' gestation. We searched the Cochrane Pregnancy and Childbirth Group's Trials Register, the Cochrane Complementary Medicine Field's Trials Register (19 January 2015) and reference lists of retrieved studies. All randomised controlled trials of any intervention for nausea, vomiting and retching in early pregnancy. We excluded trials of interventions for hyperemesis gravidarum, which are covered by another Cochrane review. We also excluded quasi-randomised trials and trials using a cross-over design. Four review authors, in pairs, reviewed the eligibility of trials and independently evaluated the risk of bias and extracted the data for included trials. Forty-one trials involving 5449 women, met the inclusion criteria. These trials covered many interventions, including acupressure, acustimulation, acupuncture, ginger, chamomile, lemon oil, mint oil, vitamin B6 and several antiemetic drugs. There were no included studies of dietary and other lifestyle interventions. Evidence regarding the effectiveness of P6 acupressure, auricular (ear) acupressure and acustimulation of the P6 point was limited. Acupuncture (P6 or traditional) showed no significant benefit to women in pregnancy. The use of ginger products may be helpful to women, but the evidence of effectiveness was limited and not consistent, though three recent studies support ginger over placebo. There was only limited evidence from trials to support the use of pharmacological agents including vitamin B6, Doxylamine-pyridoxoine and other anti-emetic drugs to relieve mild or moderate nausea and vomiting. There was little information on maternal and fetal adverse outcomes and on psychological, social or economic outcomes.We were unable to pool findings from studies for most outcomes due to heterogeneity in study participants, interventions, comparison groups, and outcomes measured or reported. The methodological quality of the included studies was mixed. Risk of bias was low related to performance bias, detection bias and attrition bias for most studies. Selection bias risk was unclear for many studies and almost half of the studies did not fully or clearly report all pre-specified outcomes. Given the high prevalence of nausea and vomiting in early pregnancy, women and health professionals need clear guidance about effective and safe interventions, based on systematically reviewed evidence. There is a lack of high-quality evidence to support any particular intervention. This is not the same as saying that the interventions studied are ineffective, but that there is insufficient strong evidence for any one intervention. The difficulties in interpreting and pooling the results of the studies included in this review highlight the need for specific, consistent and clearly justified outcomes and approaches to measurement in research studies.