Treating Even Mild Gestational Diabetes Reduces Birth Complications; Clear Benefits For Infants And Mothers

Treatment of severe gestational diabetes is known to benefit mothers and infants. Although treatment is routinely prescribed for all women with gestational diabetes, before the current study, there was no evidence to show whether treating the mild form of the condition benefited, or posed risks for, mothers or their infants.

The researchers found that, compared to the women's untreated counterparts, women treated for mild gestational diabetes had smaller, leaner babies less likely to be overweight or abnormally large, and less likely to experience shoulder dystocia, an emergency condition in which the baby's shoulder becomes lodged inside the mother's body during birth. Treated mothers were also less likely to undergo cesarean delivery, to develop high blood pressure during pregnancy, or to develop preeclampsia, a life-threatening complication of pregnancy that can lead to maternal seizures and death.

The study was conducted by researchers in the Maternal Fetal Medicine Units Network of the NIH's Eunice Kennedy Shriver National Institute of Child Health and Human (NICHD) and appears in the Oct. 1 New England Journal of Medicine. The study's first author was Mark Landon of Ohio State University.

"Whether to treat mild gestational diabetes has never been entirely clear," said study coauthor Catherine Y. Spong, chief of the Pregnancy and Perinatology Branch at the NICHD. "The study results show conclusively that both mothers and infants do better when gestational diabetes is controlled."

In addition to funding from the NICHD, the study was also supported by the NIH's National Center for Research Resources.

Gestational diabetes occurs when pregnant women who did not have any signs or symptoms of diabetes before they were pregnant develop high blood sugar levels. The condition affects from 1 to 14 percent of all U.S. pregnancies. Gestational diabetes is not well understood, but is thought to occur when hormones produced during pregnancy interfere with the body's ability to use insulin to absorb sugar from the blood.

In most cases, treatment for gestational diabetes consists of lowering blood sugar levels through proper diet and exercise. If diet and exercise alone fail to lower blood sugar levels, women may be treated with drugs that increase the body's ability to use insulin, or may be prescribed insulin itself.

The current study is the first to test whether treatment for mild gestational diabetes is beneficial. The researchers defined mild gestational diabetes as having normal blood sugar levels after fasting but abnormally high levels in at least two readings over the course of three hours after an oral glucose tolerance test, in which women consume a sugary drink. Severe diabetes was defined as high blood sugar levels even after fasting.

To conduct the study, the researchers enrolled 958 women with mild gestational diabetes. Roughly half were treated for their diabetes and half were not, receiving only standard pregnancy care.

In their statistical analysis of the study results, the researchers combined several serious potential outcomes into one figure, to represent a single and primary outcome. The primary outcome consisted of all cases of newborn death, stillbirth, newborns with low blood sugar or with high insulin levels, birth-related injuries, and high bilirubin levels (an indicator of newborn jaundice). In terms of the primary outcome, there were no differences between the two groups of women. But the women who received treatment fared significantly better than the untreated women on other measures.

Specifically, compared to women who did not receive treatment, those who did were:

• half as likely to have an unusually large baby,
• half as likely to experience shoulder dystocia during childbirth,
• four-fifths as likely to give birth by cesarean section, and
• three-fifths as likely to develop high blood pressure or preeclampsia.

"Obstetricians are concerned with the immediate risks of birth trauma which may accompany delivery of large infants to women with diabetes," Dr. Landon said.

These risks include fracture of the skull and collar bones, and injury to the nerves that connect the arm, hand and shoulder to the spine.

"Our study demonstrates that treating even mild diabetes can reduce fetal overgrowth and thus could also reduce these birth related risks."

Previous studies suggest that the higher birthweights and greater proportion of body fat seen in the newborns of women with gestational diabetes also pose increased health risks for these children later in life, Dr. Spong said. The children are more likely than other children to be overweight and, as adults, more likely to have impaired glucose tolerance, a prediabetic condition.

"The children would need to be followed long term to be certain, but it's possible that treating women with mild gestational diabetes to reduce birthweight and body fat among their newborns may benefit these children later in life," Dr. Spong said.