Hyperemesis gravidarum (HG) is a condition of pregnancy characterized by intractable nausea, vomiting, and dehydration and is estimated to affect 0.5-2.0% of pregnant women. Malnutrition and other serious complications such as fluid or electrolyte imbalances may result. Hyperemesis is considered a rare complication of pregnancy but, because nausea and vomiting during pregnancy exist on a spectrum, it is often difficult to distinguish this condition from the more common form of nausea and vomiting experienced during pregnancy known as morning sickness.
When hyperemesis gravidarum is severe and/or inadequately treated, it may result in:
- Loss of 5% or more of pre-pregnancy body weight
- Dehydration, causing ketosis, and constipation
- Nutritional disorders such as Vitamin B1 (thiamine) deficiency, Vitamin B6 deficiency or Vitamin B12 deficiency
- Metabolic imbalances such as metabolic ketoacidosis or thyrotoxicosis
- Physical and emotional stress of pregnancy on the body
- Difficulty with activities of daily living
Symptoms can be aggravated by hunger, fatigue, prenatal vitamins (especially those containing iron), and diet. Some women with hyperemesis gravidarum lose as much as 10% of their body weight. Many sufferers of HG are extremely sensitive to odors in their environment; certain smells may exacerbate symptoms. This is known ashyperolfaction. Ptyalism, or hypersalivation, is another symptom experienced by some women suffering from HG.
Hyperemesis gravidarum tends to begin somewhat earlier in the pregnancy and last significantly longer than morning sickness. While most women will experience near-complete relief of morning sickness symptoms near the beginning of their second trimester, some sufferers of HG will experience severe symptoms until they give birth to their baby, and sometimes even after giving birth.
While there are numerous theories regarding the cause of HG, the cause remains controversial. It is thought that HG is due to a combination of factors which may vary between women and include: genetics, body chemistry, and overall health.
One factor is an adverse reaction to the hormonal changes of pregnancy, in particular, elevated levels of beta human chorionic gonadotropin. This theory would also explain why hyperemesis gravidarum is most frequently encountered in the first trimester (often around 8 – 12 weeks of gestation), as hCG levels are highest at that time and decline afterward. Another postulated cause of HG is an increase in maternal levels of estrogens (decreasing intestinal motility and gastric emptying leading to nausea/vomiting).