Newswise — Many health care professionals suspect that a low glycemic diet may play a significant role in controlling pregnancy-related diabetes, but a recent review of evidence evaluating the effects of diet proved inconclusive.
One of the more troubling threats to a healthy, uncomplicated pregnancy is a metabolic disorder known as gestational diabetes mellitus. The condition affects an estimated 4 percent of mothers in the United States, and up to 14 percent worldwide. Pregnancy-related diabetes increases health risks for mothers and their babies, so researchers are searching for a means to prevent the disorder.
"The main implications of our research are suggestions for more high quality, long-term trials in healthy pregnant women, with larger sample sizes and reporting all clinically relevant outcomes, to address dietary issues more thoroughly and provide more conclusive results," said lead review author Joanna Tieu.
"Our results suggest that a low glycemic index diet may be a benefit to mother and child, however," said Tieu, at the Women and Children's Hospital at the University of Adelaide in Australia.
"This is because low glycemic index diets — such as fresh fruits and vegetables and unprocessed whole-grain foods — tend to slow down the digestion of food. Slow digestion allows the body to better adjust to the load of sugar coming in after a meal," she said.
"While our results were promising, the evidence is not sufficient to recommend changes in clinical practices, because of the limited number of trials," Tieu said.
The review appears in the latest issue of The Cochrane Library, a publication of The Cochrane Collaboration, an international organization that evaluates medical research. Systematic reviews draw evidence-based conclusions about medical practice after considering both the content and quality of existing medical trials on a topic.
The review authors found few clinical trials to include in their review. The three eligible studies included only 107 women living in the United States, Australia and the United Kingdom.
Doctors do not understand exactly what causes gestational diabetes, but they suspect that hormones from the placenta block the action of the mother's insulin. Without enough insulin, sugar (glucose) cannot enter cells, where it is needed to fuel cell activity. Instead, sugars build up in the bloodstream, causing hyperglycemia.
These excess sugars and other nutrients flow through the placenta and into the baby's cells, giving the baby more energy than it needs to develop. Stored as fat, these excess sugars may cause the baby to grow quite large — more than 8.8 pounds — or greater than the 90th percentile, compared to other babies.
A large baby may get wedged on the mother's pubic bone during delivery, for example, putting the baby at risk for a number of health problems, including fractures or brachial plexus injuries, which can damage the network of nerves connecting the spine with the shoulder, arm and hand.
"Gestational diabetes also has been associated with spontaneous labor and premature birth," Tieu said. "And children of women with gestational diabetes are at increased risk of obesity, glucose intolerance and diabetes in late adolescence and young adulthood."
Mothers with gestational diabetes are at increased risk for preeclampsia (hypertension) or placental abruption during pregnancy. Induced births or Caesarean sections are more common, adding even more health risks. These women also have an increased risk of developing diabetes in the future.
Obstetrician Seth Brody, with Wake Medical Center in Raleigh, N.C., said that very large studies with longer follow-up are necessary to determine whether dietary changes can alter significant health outcomes. He suggests that in the future studies, researchers should go beyond simply knowing the difference in babies' weights and serum glucose levels because these are not health outcomes of clinical significance.
"If the difference in birth weight were significant enough to be reflected as a difference in birth injury rates, Caesarean delivery rates and the need for operative deliveries, then that difference is of clinical importance, as is studying rates of brachia plexus injuries, fractures or neonatal mortality." he said. "If a low glycemic diet altered the incidence of treatment for short- or long-term metabolic issues for either mom or baby, then those would be very important health outcome differences to determine, as well.
"At this point, it is most reasonable to continue to recommend the appropriate diet, weight gain, and exercise guidelines to all pregnant women, as outlined by the American College of Obstetrics and Gynecology," Brody said.
The Cochrane Collaboration is an international non-profit, independent organization that produces and disseminates systematic reviews of health care interventions and promotes the search for evidence in the form of clinical trials and other studies of interventions. Visit http://www.cochrane.org for more information.
American College of Obstetrics and Gynecology guidelines for pregnant women are available at http://www.acog.org
Tieu J, Crowther CA, Middleton P. Dietary advice in pregnancy for preventing gestational diabetes mellitus (Review). Cochrane Database of Systematic Reviews 2008, Issue 2.