A new study suggests that severe morning sickness may have a genetic component, because it is more likely to affect women whose mothers or sisters were also affected. Focusing on hyperemesis gravidardum (HG) - a type of morning sickness that causes severe vomiting and nausea in around one percent of pregnant women - the study found that women whose sisters had HG were 17 times more likely to develop HG themselves.
The researchers looked at 207 women with one or more sisters that had HG and compared them to a control group of 110 of the patients' female friends who had nausea-free pregnancies. They found that 14 percent of women who had HG also had an affected sister versus one percent of women who did not have HG. If other severe forms of morning sickness were taken into account then 34 percent of women with HG also had an affected sister compared with eight percent of controls. The study also found similar ratios when looking at mothers who had HG instead of sisters.
Dr Marlena Fezjo, a geneticist at the University of Southern California-Los Angeles and lead author of the study said: 'The degree of heredity is very exciting because it suggests genes are involved, and when we find those genes we may finally understand the cause of severe nausea in pregnancy and be able to make new treatments that are designed to treat the cause rather than the symptoms'. However, Dr Andrej Grjibovski from the Norwegian Institute of Public Health, points out that women with HG might have been more likely to volunteer for the study if they had relatives with HG.
These findings backup earlier evidence that HG may have a heritable component, as suggested in an analysis of birth records, which found an increased risk of severe morning sickness in women whose mothers had the condition, and that identical twins are more likely to both develop the condition compared with non-identical twins.
HG is a significant problem that leads to the hospitalisation of more than 59,000 women a year in the US. Dr Fezjo and her team are now planning to compare the genes of women with and without HG, to identify those genes that may predispose women to the condition.