Abstract: 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.

Plain-language summary: This review found a lack of high-quality evidence to back up any advice on which interventions to use. We examined 41 randomised controlled trials that included 5449 women in early pregnancy. These studies examined the effectiveness of many treatments including acupressure to the P6 point on the wrist, acustimulation, acupuncture, ginger, chamomile, vitamin B6, lemon oil, mint oil, and several drugs that are used to reduce nausea or vomiting. Some studies showed a benefit in improving nausea and vomiting symptoms for women, but generally effects were inconsistent and limited. Overall, studies had low risk of bias related to blinding and reporting on all participants in the studies. However some aspects of the studies were reported incompletely in a way that meant how participants were allocated to groups was unclear and not all results were fully and clearly reported. Most studies had different ways of measuring the symptoms of nausea and vomiting and therefore, we could not look at these findings together. Few studies reported maternal and fetal adverse outcomes and there was very little information on the effectiveness of treatments for improving women's quality of life.