This is one of the first studies to investigate the recurrence of very severe morning sickness across generations.
“The study provides new knowledge which in turn may help us find the causes of severe morning sickness,” Åse Vikanes at the Norwegian Institute of Public Health said.
The study has investigated 2.3 million birth records in Norway from 1967-2006, based on data from the Norwegian Birth Registry.
Genes or environment?
The causes of severe morning sickness are not known and knowledge on whether the illness is genetically transmitted or caused by environmental factors is limited. Former studies suggest that there could be a genetic link between mother and child.
|Facts about severe morning sickness
Severe morning sickness (hyperemesis gravidarum) is defined as excessive nausea and vomiting in pregnancy, occuring in up to 2 per cent of pregnancies. It is the most common cause of admission to hospital in early pregnancy. The illness may lead to weight loss, nutritional and vitamin deficiencies. It is also associated with adverse pregnancy outcomes such as low birth weight and preterm birth.
Results from this study show that if the mother suffered from severe morning sickness, daughters were 3 per cent more likely to develop the condition in their own pregnancies, compared to 1.1 per cent among women, whose mothers did not suffer from the illness.
The results also show that female partners of sons whose mothers had suffered from the illness only had 1.2 per cent risk of developing severe morning sickness.
“Severe morning sickness tends to recur in pregnancies in the same woman. An increased risk across generations further suggests that genetic factors are important. The fact that the risk is passed on to daughters but not to female partners of sons, suggests that the mother’s genes are more important the fetal genes,” Vikanes said.
It is, however, possible that the risk is not genetically transmitted, but caused by common environmental factors shared by mothers and daughters such as nutrition, other lifestyle factors and infections.
New perspective and implications for clinicians
The results from this study provide new knowledge on possible causes of severe morning sickness and should stimulate further research into the aetiology.
“This as well as an understanding of the psychological consequences of experiencing severe nausea and vomiting, provides a new perspective on the illness and could be helpful for clinicians who treat and counsel women with severe morning sickness,” Vikanes said.
Vikanes, Åse; Skjærven, Rolv; Grjibovski, Andrej M; Gunnes, Nina; Vanger, Siri; Magnus, Per. Recurrence of hyperemesis gravidarum across generations: population based cohort study. British Medical Journal 2010;340;c2050