Even though nearly all women experience at least a little nausea or vomiting during pregnancy, there isn't much solid evidence to suggest the best treatments, a research review concludes.

Ginger, vitamin B6 or antihistamines, for example, may ease mild nausea, while severe vomiting that carries a risk of dehydration and malnutrition can sometimes be improved by corticosteroids, the study found.

The trouble is there's scant evidence to suggest how one treatment might stack up against available alternatives, said lead study author Catherine McParlin of Newcastle University in the U.K.

"Women react differently and may need to try different treatment options before they find something that is effective for them," McParlin said by email.

"When it comes to evidence of the effectiveness of specific treatments for different levels of condition severity, the research to date has mostly been of low quality, with many trials badly designed and/or badly reported, with few direct comparisons between treatments especially in severe cases," McParlin added.

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Nausea and vomiting are common during pregnancy, affecting up to 85 percent of women, the researchers note in JAMA.

Sometimes called morning sickness, in reality it can occur throughout the day. Often, symptoms may be mild and ease up after the first few months of pregnancy.

The most severe form, hyperemesis gravidarum, affects up to 3 percent of pregnant women and can require hospitalization to provide nutrition through a feeding tube.

To assess the effectiveness of a variety of treatments for nausea and vomiting during pregnancy, researchers analyzed data from 78 previously published studies with 8,930 patients combined.

For mild symptoms, ginger, vitamin B6, antihistamines and metoclopramide (Reglan) were all more effective than a placebo pill, the study found. Pyridoxine-doxylamine (Diclectin) and ondansetron (Zofran) both beat a placebo for moderate symptoms.

When women have moderate to severe symptoms, they may get better results by taking pyridoxine-doxylamine preemptively to reduce the risk of recurrent vomiting instead of waiting to take this medicine until symptoms return, one study of 60 women in the analysis suggests.

Another study found ondansetron more effective at curbing moderate to severe nausea in the first few days of use than metoclopramide, but no difference in how many times women vomited.

With hyperemesis gravidarum, women have fewer options and there's even less evidence, the study authors note.

Corticosteroids appeared superior to metoclopramide for reducing vomiting episodes in an analysis of three studies of women with the most severe symptoms.

One limitation of the analysis is that researchers lacked data to compare side effects for babies associated with different treatments the authors note.

The findings aren't surprising because ethics limit testing experimental drugs in pregnancy, particularly during the early months when medications might harm fetal development, said Angela Lupattelli, a pharmacy researcher at the University of Oslo in Norway who wasn't involved in the study.

Complicating matters, there aren't good objective tests to assess nausea symptoms, Lupattelli added by email.

"In case of mild symptoms, women are recommended to change their dietary habits first, and then try non-pharmacological options," Lupattelli said.

Some women do well with small, frequent meals that are high in protein and avoiding strong odors or other identifiable triggers for nausea, while others respond well to ginger, said Dr. Siripanth Nippita, a researcher at Harvard University in Boston who wasn't involved in the study.

"Other women may need medication," Nippita added by email. "Pregnant women should let their obstetricians know early on how nausea and vomiting are affecting them, so they can get the help they need."