Upside of morning sickness:

There's an upside to being struck down by nausea and vomiting in pregnancy – it could mean your baby is healthier and more intelligent.

Researchers from The Hospital for Sick Children and the University of Toronto in Canada reviewed 10 previous studies involving about 850,000 women and found that those who suffered nausea and vomiting during pregnancy gave birth to bigger, healthier babies and had fewer miscarriages.

Morning sickness was also associated with better infant development and fewer birth defects, and when the researchers tested the babies years later, they found they scored higher on IQ, language and behaviour tests.

They found that mothers aged 35 and over, who have a higher risk of miscarriage, were also less likely to have one if they suffered morning sickness.

Only 6.4% of women suffering nausea and vomiting had a pre-term birth, compared to 9.5% of those without symptoms.

The risk of birth defects dropped by between 30 and 80% for babies whose mother had morning sickness.

"Women with moderate to severe nausea and vomiting in pregnancy often experience major negative impact on their health and quality of life," said lead author Dr Gideon Koren.

"Our analysis indicates that reassuring these women that their severe symptoms may confer favourable foetal outcome in their unborn babies is logical.  While this may not be the case in women experiencing hyperemesis gravidarum (pregnancy sickness), it does seem to be valid for the majority of pregnancies."

Around 85% of pregnant women suffer morning sickness, which is believed to be caused by rapid increases in human gonadotropin, a hormone that is released by the placenta during pregnancy.

This, and other hormones, are believed to create a better environment for babies to grow.

Researchers compared nausea and vomiting data with miscarriage rates, prematurity, birth weight, congenital abnormalities, such as cleft palate and cardiac defects, plus long-term child development.

Dr Koren said taking medication to reduce morning sickness does not affect women's hormone levels, so would not counteract these positive outcomes.