Morning sickness is technically known as hyperemesis gravidarum. It involves severe vomiting, from between once to around 50 times a day. The causes remain unknown.
One new insight into the condition has come in the form of the sex of the child that the woman eventually gives birth to. A Swedish study of 1.7 million pregnancies has discovered two tendencies:
Firstly, less well-educated women are more likely to develop morning sickness.
Secondly, women who have high levels of morning sickness are more likely to have daughters.
With the first insight, the general trend here is that women who left school at 16 were 76 percent more likely to develop extreme morning sickness compared with women with college degrees or higher.
With the second point, regardless of education, women who experience the highest levels of morning sickness are more likely to give birth to daughters, Speaking with New Scientist magazine, Dr. Lena Edlund said: “Normally, slightly more boys than girls are born, we don’t quite know why that is.” She goes onto speculate that other evidence suggests stress affects the sex ratio of children born to mothers who experience different levels of emotional anxiety.
The proportion is that women with high levels of morning sickness give birth to 56 times out of 100. This was based on a survey of 18,000 women. Care needs to be made when interpreting the data since it was made only on one country (Sweden) at one time point.
The findings are published in the journal Economics and Human Biology, in a paper called “An adaptive significance of morning sickness? Trivers–Willard and Hyperemesis Gravidarum.”
