Nausea and vomiting in pregnancy is among the most universal and most poorly managed symptoms in obstetrics. It affects up to 80 percent of pregnant women, typically begins around five to six weeks of gestation, peaks between eight and ten weeks, and resolves by fourteen weeks in most but not all cases. The name morning sickness is a misnomer: in the majority of affected women, nausea is present throughout the day. Understanding the mechanisms and the evidence base for management allows for a more effective response than the commonly given advice to eat dry crackers.
The Biological Mechanism
The primary driver of nausea in pregnancy is human chorionic gonadotropin, the hormone produced by the developing placenta that rises steeply in the first trimester. HCG peaks at eight to ten weeks, the same time at which nausea is typically worst, and its decline correlates with symptom resolution in most women. Women with twin pregnancies, who produce more HCG, report more severe nausea. Women with hyperemesis gravidarum, the severe form of pregnancy nausea requiring medical intervention, have measurably higher HCG levels. The stomach slows its emptying rate under the influence of pregnancy hormones, and this delayed gastric emptying increases the duration and severity of nausea after eating.
Dietary Strategies with Evidence
Frequent small meals that prevent an empty stomach are the most consistently effective dietary strategy, as nausea is typically worst on an empty stomach due to the interaction of stomach acid with gastric mucosa in the absence of food. Carbohydrate-rich, low-fat foods empty the stomach more rapidly than fatty foods and are generally better tolerated. Eating a small amount of plain food, such as a plain biscuit, before getting out of bed can prevent the peak of morning nausea that occurs when blood sugar has been low overnight.
Vitamin B6 and Ginger: The Evidence
Vitamin B6 at 10 to 25 milligrams three times daily has consistent evidence from randomised controlled trials for reducing nausea severity in pregnancy. A Cochrane review found that vitamin B6 significantly reduced nausea scores compared to placebo, with good safety data at doses up to 200 milligrams per day. Ginger, at doses of 1 to 1.5 grams per day of dried ginger or ginger extract, has also been evaluated in multiple randomised trials and found to significantly reduce nausea and vomiting compared to placebo. A meta-analysis by Viljoen et al. found ginger significantly superior to placebo for both nausea and vomiting outcomes with no reported adverse effects. Doxylamine combined with vitamin B6 is the only licensed combination treatment for nausea in pregnancy in the UK and is available on prescription when over-the-counter measures are insufficient.
- Eat small amounts every one to two hours: an empty stomach significantly worsens nausea
- Keep plain crackers or dry cereal beside the bed and eat a small amount before sitting up in the morning
- Vitamin B6 10 to 25mg three times daily has randomised trial evidence for reducing nausea: safe throughout the first trimester
- Ginger in any form, fresh, dried, as tea, or as crystallised ginger, at 1 to 1.5g daily is evidence-based and safe
- If nausea is preventing adequate fluid and food intake for more than 24 to 48 hours, contact your midwife or GP: hyperemesis gravidarum requires medical management and untreated dehydration carries risk to the pregnancy
Sources
- Viljoen, E., et al. (2014). A systematic review and meta-analysis of the effect and safety of ginger in the treatment of pregnancy-associated nausea and vomiting. Nutrition Journal, 13, 20.
- Koren, G., et al. (2014). Morning sickness: can the mother's suffering improve the child's health? Current Drug Safety, 9(3), 156-163.
- Festin, M. (2014). Nausea and vomiting in early pregnancy. BMJ Clinical Evidence, 2014, 1405.