The many myths surrounding morning sickness are being wheeled out yet again, given the news that a royal is suffering from it.

First of all 'morning sickness' is misnamed as it only occurs in the morning in less than 20% of women. Despite reassurances currently being published that the Duchess's torment is going to be very temporary, in fact only half of women with nausea and vomiting during pregnancy are completely relieved by 14 weeks' gestation. Plus it can be extremely debilitating with up to a quarter of women in one study with symptoms requiring time off work as a result.

Miserable though it may be to experience as a condition, in fact 'morning sickness' (if it's not of the rarer more severe kind), oddly enough, can be good news for a pregnancy. It's associated with lowered risk for miscarriage, pre-term birth, low birth weight, and perinatal death. However it can also be associated with serious medical conditions which need to be screened for and treated, but most often it occurs in medically normal pregnancies.

In 2009 a study published in 'The Journal of Pediatrics' from the Hospital for Sick Children, Toronto, provoked controversy when it found nausea and vomiting during pregnancy was significantly associated with better IQ test results in children aged three to seven years after delivery. A battery of psychological tests were involved including measures of intelligence, neurocognitive abilities and behavior problems.

The study entitled 'Long-term Neurodevelopment of Children Exposed to Maternal Nausea and Vomiting of Pregnancy and Diclectin' - by Irena Nulman, Gideon Koren and colleagues, found the more severe the nausea and vomiting during pregnancy, the better the child's eventual scores across the range of tests.

No one knows exactly why nausea and vomiting during pregnancy is generally good for the foetus, but this has led to a 'Maternal and Embryo Protection Hypothesis', which argues its purpose may be to shield the mother from contaminated food, so protecting the developing foetus against potentially threatening toxins and bugs.

Some have hypothesised that raised hormone levels during pregnancy, such as oestrogen and Human Chorionic Gonadotropin levels make the smell or olfactory system in the female brain hyper-sensitive. One theory is that it's smells which might be the primary driver of nausea and vomiting during pregnancy, and extra-sensitivity to odours protects mothers from imbibing hazards. It is also established that Asian women have more troublesome vomiting and this seems to be due to the structure of Human Chorionic Gonadotropin.

Many features of nausea and vomiting during pregnancy suggest an evolutionary adaptive design. For example, Samuel Flaxman and Paul Sherman from the Dept of Neurobiology and Behavior, Cornell University, contend it's therefore no accident it tends to occur during the most sensitive period of embryogenesis (weeks five-18). They also point out in their commentary in the academic journal 'Trends in Ecology & Evolution', it causes physical expulsion of and subsequent aversions to the foods that are most likely to be hazardous including meats, caffeinated beverages and pungent vegetables. They also note the intriguing absence of nausea and vomiting during pregnancy in seven societies on four continents lacking such dietary triggers.

Another theory is that the food aversion is a completely incidental and an unwanted side-effect, as it's a direct effect on the foetal brain or the placenta of high levels of hormones of pregnancy which cause nausea, which is why there appears to be an association with baby benefits.

Whether nausea and vomiting has a natural protective or positive purpose during pregnancy raises a conflict for doctors as to whether women should be treated to suppress symptoms, or encouraged instead to 'ride them out'. This is made all the more difficult given the long history of some anti-nausea treatments when ingested, causing congenital problems. Severe nausea and vomiting in pregnancy, otherwise known as hyperemesis gravidarum, should definitely be treated as it can result in life-threatening malnutrition and liver damage, but it's rare, and affects less than 1% of pregnant women. The most dangerous consequence is for the woman to suffer vitamin deficiencies and this can cause maternal brain damage.

Women suffering from so-called normal nausea and vomiting are often desperate, and any treatment which doesn't involve taking something, given the risks to the foetus, should be welcomed.

This condition also responds to vitamin supplementation, acupuncture and acupressure. These treatments can also improve mood during pregnancy and the emotional impact of nausea and vomiting during pregnancy is extremely important.