Nausea and vomiting are very common complaints during the early weeks of pregnancy. Due to the possible harmful side-effects that conventional medicine may pose to the unborn fetus, many mothers choose not to use it, and are left helpless against this burden. Nausea and vomiting of pregnancy (NVP) is commonly referred to as morning sickness (although it can occur at any time of the day or night), and affects about 80-90% of pregnant women in varying degrees [1, 2]. Most of these women will experience both nausea and vomiting, and some only nausea without vomiting or retching, but vomiting alone is rare . Symptoms usually appear at 4–9 weeks of gestation, reaching a peak at 7–12 weeks, and subsiding by week 16. About 15-30% of pregnant women’s symptoms will persist beyond 20 weeks, or even up to the time of delivery [1, 2]. Hyperemesis gravidarum (HG) is severe and persistent vomiting during pregnancy, which can lead to dehydration, electrolyte disturbances and liver damage, possible fetal damage and in extreme cases, the death of the mother [1, 3–5]. Women with HG usually need to be hospitalized  and it occurs in approximately 2% of pregnancies [1, 2].
The exact cause of NVP remains unclear, and is probably multifactorial. Theories include the rapid increase in hormones such as estrogen and human chorionic gonadotropin (hCG),  or Helicobacter pylori (H.pylori) infection, as well as psychological and genetic predisposition [2, 6]. Severe NVP and HG can lead to maternal malnourishment and weight loss, leading to negative fetal outcomes including low birth weight and preterm birth . Maternal complications include acute renal failure, esophageal rupture, coagulopathy and on rare occasions, Wernicke’s encephalopathy . The negative effects of NVP described clearly show the importance of managing and treating NVP and HG as early as possible, and not considering NVP as merely an unpleasant part of pregnancy that has to be endured and suffered through.
Pharmacological treatment of NVP is complicated due to the fact that during pregnancy, many physiological changes occur, including gastro-intestinal motility, plasma volume and glomerular filtration . These factors all influence the distribution, absorption and excretion of drugs and due to this reason, not all drugs are safe during pregnancy. Many drugs cross the placenta by simple diffusion and can affect the fetus directly . Non-pharmacological treatment of NVP includes ginger and simple lifestyle changes that have been described in the literature . Acupressure is also a safe and non-invasive treatment for NVP, although there is a lack of evidence of efficacy [1, 6].
Ginger (Zingiber officinale Roscoe) is widely used, with the most common ailments currently being treated with ginger including nausea, vomiting, pregnancy-associated morning sickness, motion sickness and indigestion [8–12]. There is mixed scientific evidence for the use of ginger in NVP [8, 10]. It should be noted that high doses of concentrated ginger in the form of powder or herbal tinctures can increase bleeding risk by decreasing platelet-aggregation, and also increase stomach acid production, especially if taken with other herbs or medicines with the same effect [8, 9, 13]. Thus, ginger supplementation can have additive or competitive interactions with some medicines.
Several studies have been performed on the use of ginger as an anti-emetic for use with post-operative nausea and vomiting, motion sickness and vertigo and chemotherapy-induced nausea and vomiting [8, 9, 11, 14]. The ingestion of oral ginger in a fasting state or after food intake results in an increase in gastro-duodenal motility , which could be a possible mechanism of action for the reduction in nausea and vomiting.
Currently no clear guidelines are available for ginger’s use in the treatment of NVP, despite some literature available on the subject [10, 16, 17]. A systematic review of the available literature (also focusing on safety aspects) can provide the best current evidence regarding possible benefits or risks for the clinical use of ginger to treat NVP.
The primary objective of this systematic review (SR) was to assess the effectiveness of ginger in the treatment of NVP. The secondary objective was to assess the safety of orally administered ginger in the treatment of NVP, by identifying adverse events or side-effects (if any), and to classify them as major (serious complications detrimental to the mother or fetus), or minor (discomfort, but manageable side-effects).