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Morning Sickness: What is Hyperemesis Gravidarum?

Up to 85% of women experience occasional nausea and vomiting during pregnancy (usually referred to as “morning sickness”); hyperemesis gravidarum (HG) is an extreme version of this relatively common pregnancy symptom. Affecting up to 2% of pregnancies, HG has no standard definition but is generally regarded as extreme nausea and vomiting when other causes (such as a thyroid disorder or infections) have been ruled out. Most women diagnosed with HG will experience more than three episodes of vomiting per day and will have lost up to 5% of their pre-pregnancy weight and/or have ketones in their urine.

HG is the most common reason women are admitted to hospital in their first trimester. Perhaps one of the most well known sufferers of HG is the Duchess of Cambridge, Catherine Middleton, who experienced HG with each of her three pregnancies and was hospitalised with the first. Hospitalisation is required when a patient becomes clinically dehydrated, is unable to control their nausea and cannot eat or drink anything without vomiting.

The causes of HG are likely varied, but high levels of the pregnancy hormone, human chorionic gonadotropin (HCG) is considered to be partly to blame. Elevated levels of oestrogen can also contribute to HG. Other risk factors include a history of HG in a prior pregnancy, having a family member with the condition, multiple pregnancies, obesity and previous diagnosis of an eating disorder.

There are various non-pharmacological treatment options for HG. Some studies have shown that women who take a multivitamin at the time of conception are less likely to require medical intervention for pregnancy-induced vomiting. Which suggests that prenatal vitamins may have multiple health benefits if taken from the time you start trying to conceive. Other treatments include avoiding foods or smells that trigger nausea, resting, and eating small, frequent meals. Ginger can also help to alleviate gastrointestinal discomfort. Bracelets providing pressure to points on the wrist have been studied, but most of this work has been poor quality and further validation is required.

As for pharmaceutical agents, there are medications that have been shown to help minimise the effects of HG. Pyridoxine (vitamin B6), used with or without doxylamine, has been shown to effectively treat nausea and vomiting in many pregnant women. Your doctor will be able to advise you on the safety and efficacy of other anti-nausea (antiemetic) medications. After 12 weeks gestation, steroids are generally considered to be safe for the developing foetus and these can also be used to alleviate the effects of HG.

Following a diagnosis of HG, it is entirely normal to worry that it might be affecting your developing baby. However, the good news is that most pregnancies progress just fine. Your doctor will monitor you closely throughout your pregnancy, but there is no reason to anticipate additional complications. Some studies have shown a higher incidence of low birth weight infants born to women with HG, but this finding is not consistent across all cases. There are no studies showing adverse developmental outcomes in babies born to mothers with HG.


  • Jueckstock, Jk, et al. “Managing Hyperemesis Gravidarum: a Multimodal Challenge.” BMC Medicine, vol. 8, no. 1, 2010, doi:10.1186/1741-7015-8-46.
  • American Congress of Obstetricians/Gynecologists
  • Practice Bulletin #52: Nausea and Vomiting of Pregnancy.

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