Up to 80 percent of all women experience morning sickness in early pregnancy. Between 0.8 and 3.2 per cent develop extreme nausea and vomiting in pregnancy. Fluid loss and nutritional deficiencies make this condition among the most frequent causes of hospitalisation among pregnant women. Hypermesis is also associated with a number of complications such as low birth weight and greatly reduced quality of life of the mother. The thesis is based on data from the Norwegian Mother and Child Cohort Study and The Medical Birth Registry of Norway.
In her thesis, Vikanes found large ethnic differences in prevalence of hyperemesis. Women born in India, Sri Lanka or in sub-Saharan Africa are three times more likely to develop the condition compared to women born in Norway. These differences could not be explained by differences in socioeconomic conditions or parental consanguinity. The length of residence in Norway seems to affect the risk of hyperemesis in varying degrees depending on the mother's country of birth.
Tripled risk between generations
There is a tripled risk of developing hyperemesis among ethnic Norwegian women if their mothers had the disease in one or more of their pregnancies. Partners of the sons who were born after pregnancies complicated with hyperemesis had no increased risk of developing the condition.
Transmission from mothers to daughters but not to sons suggests that maternal genes are responsible, although the significance of environmental factors that persist in families over generations cannot be ruled out.
Smoking and weight influence
Non-smoking women with lower or higher body mass index (BMI) than normal, meaning BMI lower than 18.5 kg/m2 or higher than 24.9 kg/m2, had increased risk of developing hyperemesis. Smokers had a reduced risk of hyperemesis compared to non-smokers.
- These findings are all stepping stones in exploring possible causes of the enigma of hyperemesis gravidarum. However, I would emphasise that the latter results are not an argument for smoking," said Vikanes.