Researchers at Toronto's Hospital for Sick Children are reporting that babies born to women who experience morning sickness score higher on IQ tests when they're older.
The more severe the nausea and vomiting, the higher the scores.
The study, to be published Thursday by the Journal of Pediatrics, is being described as the first to assess the impact of morning sickness on a child's brain development.
Morning sickness — which can actually occur all day — is the most common condition of pregnancy, affecting as many as 80 per cent of pregnant women. It's the most common reason for a woman to be hospitalized in her first trimester, and, in severe cases, can lead to dehydration, salt and vitamin imbalances and weight loss.
In Canada, the only approved drug for nausea in pregnancy is Diclectin. But many women "are afraid to take anything" during pregnancy, says Dr. Gideon Koren, director of the Motherisk Program at Sick Kids and the study's principal investigator. Motherisk has a special hotline just for morning sickness. It receives about 30 calls a day from women in Canada and the U.S.
Koren says Diclectin's approval was based mostly on "morphological" studies showing "that the kids don't have malformations.
"It was very important for us to be able to show that, OK, the babies don't have malformations but they also develop right."
The study, which was partially funded by Duchesnay Inc., the Quebec drug company that markets Diclectin, involved 121 women who called Motherisk's NVP (nausea and vomiting of pregnancy) hotline from 1998 to 2003.
The women and their babies were split into three groups: 45 mothers who experienced morning sickness who took Diclectin; 47 who had morning sickness but who didn't take the drug; and 29 women who didn't have any morning sickness at all. The women had similar IQs and came from similar socioeconomic and educational backgrounds.
When the children were ages three to seven, they were assessed with a battery of age-appropriate psychological tests.
All scored within the normal range of IQ. But the children whose mothers had morning sickness scored higher on performance IQ (games and tasks), verbal fluency and "phonological processing" — how well children process the sounds of letters and letter combinations. Taking Diclectin did not appear to have any negative affect on brain development, the researchers say.
"Probably even more interesting, the achievements of the babies of moms who did not have morning sickness were not as high," Koren says.
"It's important to stress it was not mental retardation or anything," says Koren, an associate professor of pediatrics at the University of Toronto who has been a paid consultant for Duchesnay.
The difference "wasn't clinically very important," he says. "It was a few points of IQ, and other functions such as language development.
"This does not mean that a woman who does not have morning sickness should be worried, that's not the idea here."
Rather, he says, the study should offer some comfort to women who do.
Other studies have shown that women who experience morning sickness have a lower risk of miscarriage and fewer heart malformations in their babies.
Morning sickness is a poorly understood phenomenon.
"Some people say that if it was a man's condition it would be known by now," Koren says. Hormones secreted by the placenta are thought to cause the "yuckiness" of morning sickness. No one knows which hormone. "But clearly something that is associated with the morning sickness confers better outcomes. We said, 'Let's see if it's true for brain development.' "
Some evolutionary biologists believe morning sickness is a defence mechanism of the body to let women vomit out things she might have eaten that may harm the fetus.
"The most important implication for women is, if you have moderate or severe morning sickness, don't hesitate to treat it with Diclectin. The drug is safe," Koren says. "You don't need to suffer from symptoms and you don't be afraid that the condition itself will affect (the baby's) long-term outcome."
The study was also supported by the Canadian Institutes of Health Research, SickKids Foundation and Research Leadership for Better Pharmacotherapy in Pregnancy and Breastfeeding.