What is hyperemesis gravidarum? Kate Middleton's acute morning sickness explained

Acute morning sickness, known as hyperemesis gravidarum, is a serious medical condition with potential consequences for mother and baby. While seven out of ten pregnant women suffer nausea, usually in the first three months, some are sick morning noon and night throughout, vomiting as much as 25 times a day.

Until the 1950s, women even died from the condition through becoming dehydrated – Charlotte Bronte is believed to have been a victim. Now dehydration can be treated with a drip and is a common reason for hospitalisation accounting for more than 25,000 admissions a year.

Others cannot cope with the sickness and seek a termination. Since thalidomide led to children born with birth defects in the 1960s , there is a fear of prescribing anything in pregnancy and the condition is consequently under-treated.

A Swedish study in The Lancet in 1999 suggested women suffering from the condition were slightly more likely to be carrying a girl.