Studies Suggest Ways to Improve Gestational Diabetes Outcomes

Tara Haelle

April 15, 2016

Two new studies suggest that earlier screening for gestational diabetes and a lower diagnostic threshold for treatment each may reduce the maternal and fetal risks associated with the condition.

In the first study, published online April 7 in Diabetes Care, Ulla Sovio, PhD, from the University of Cambridge in the United Kingdom, and colleagues report on the interaction between obesity and gestational diabetes (GDM) with regard to fetal growth. In the second study, published online April 4 in Obstetrics & Gynecology, Lorie M. Harper, MD, from the University of Alabama at Birmingham, and colleagues compared GDM treatment outcomes of women diagnosed with GDM based on Carpenter-Coustan criteria vs those diagnosed using National Diabetes Data Group criteria.

"Both of the studies emphasize evaluating individual women, and there's enough data now, including with these two studies, to say that the risks of higher blood glucose and metabolic dysfunctions that accompany obesity definitely impact pregnancy and baby health," Amy Valent, DO, an assistant professor in the Division of Maternal Fetal Medicine at Oregon Health & Science University, Portland, who specializes in metabolic disorders during pregnancy, told Medscape Medical News. Both studies, she added, show that treating and controlling GDM even with earlier screening or broader criteria can improve outcomes.

"Physicians and practices should really communicate with all pregnant women about the importance of healthy food choices and exercise during pregnancy to improve the environment the baby is developing in," Dr Valent said. "Using lower cutoffs such as Carpenter-Coustan criteria or the earlier cutoff with the International Association of Diabetes and Pregnancy Study Groups criteria will identify more women with higher blood sugars who can make a difference in their pregnancy outcomes."

In the first study, Dr Sovio and colleagues found that fetuses of mothers with obesity and/or GDM grew more quickly between 20 and 28 weeks of gestation than the fetuses of mothers with neither condition. The US Preventive Services Task Force and the American College of Obstetricians and Gynecologists currently recommend that glucose screening for GDM occur between 24 and 28 weeks' gestation.

"We found that excessive fetal growth preceded clinical diagnosis of GDM," the authors write. "These data suggest that the onset of fetal growth disorder in GDM predates the usual time of screening."

The researchers prospectively followed a cohort of 4069 nulliparous women and used sonography to measure fetal abdominal and head circumferences at 20 and 28 weeks of gestation. Among these women, 4.2% received a gestational diabetes diagnosis after 28 weeks of gestation. "Women who subsequently developed GDM were older, shorter, were more likely to be obese, gained slightly less weight, and were more likely to have induced labor and caesarean delivery," the authors report.

Although fetal head and abdomen size at 20 weeks did not predict a GDM diagnosis, fetuses of women with GDM were twice as likely to have an abdominal circumference above the 90th percentile at 28 weeks' gestation (adjusted relative risk [aRR], 2.05; 95% confidence interval [CI], 1.37 - 3.07). These fetuses' head-to-abdominal circumference ratio was also nearly twice as likely to be below the 10th percentile (aRR, 1.97; 95% CI, 1.30 - 2.99).

"The current observations cannot be explained by misclassification of nongestational glycemic dysregulation as GDM because the results were very similar when confined to women with confirmed normal postpartum glucose tolerance," the authors add.

Similarly, fetuses of mothers with obesity were twice as likely to have an abdominal circumference above the 90th percentile (aRR, 2.04; 95% CI, 1.62 - 2.56) and 1.5 times more likely to have a head-to-abdomen circumference ratio below the 10th percentile (aRR, 1.46; 95% CI, 1.12 - 1.90).

Among mothers with both obesity and GDM, at 28 weeks, fetuses were five times more likely to fall above the 90th percentile for abdominal circumference (aRR, 4.52; 95% CI, 2.98 - 6.85) and had almost triple the risk for a head-to-abdomen circumference ratio below the 10th percentile (aRR, 2.80; 95% CI, 1.64 - 4.78). Further, the risk of being large for gestational age at birth was quadrupled for those fetuses with abdominal circumferences above the 90th percentile.

"[O]ur data suggest that screening prior to 28 [weeks of gestational age] may be one approach to improving the short- and long-term outcomes of pregnancies complicated by GDM," the authors write. "In fact, the current data indicate that any intervention aimed at reducing the risk of [large for gestational age] in the infants of obese women may need to be implemented before 20 [weeks of gestational age]."

Dr Valent pointed out that American College of Obstetricians and Gynecologists and the American Diabetes Association already recommend early screening for GDM when prenatal care begins for populations at higher risk for the condition, such as those who have obesity; who previously had GDM, metabolic syndrome, prediabetes, polycystic ovarian syndrome, or another metabolic dysfunction. The American Diabetes Association also recommends early screening for those who previously delivered a baby heavier than 9 pounds, those with first-degree family members with diabetes, or those with high blood pressure or an abnormal cholesterol profile, Dr Valent said. In addition, racial and ethnic populations at higher risk for GDM include African Americans, Native Americans, Asian Americans, Pacific Islanders, Alaskan Americans, and Hispanics

"I think many physicians are aware that screening should be performed early," Dr Valent said. "The question and some of the controversy is how to screen them early in the pregnancy."

Dr Harper and colleagues largely explored that question in the second study by conducting a secondary analysis of a randomized trial that assessed treatment of mild GDM based on Carpenter-Coustan criteria. Among 931 patients, 389 were women diagnosed with GDM based on Carpenter-Coustan criteria, of whom 50.4% were randomly assigned to receive treatment. Among the 542 women meeting GDM criteria from the National Diabetes Data Group, 51.7% were randomly assigned to receive treatment.

The researchers compared maternal outcomes of pregnancy-induced hypertension, shoulder dystocia, maternal weight gain, and cesarean delivery and neonatal outcomes of gestational age, macrosomia (>4000 g), fat mass, small for gestational age, and a composite outcome of perinatal death, birth injury, hypoglycemia, hyperbilirubinemia, and hyperinsulinemia. For all outcomes, the researchers found no significant interaction between the different sets of diagnostic criteria.

Among those diagnosed using Carpenter-Coustan criteria, the number needed to treat was 7 for cesarean delivery, 17 for gestational hypertension or preeclampsia, 187 for shoulder dystocia, 23 for large for gestational age, and 16 for macrosomia. For those diagnosed on the basis of National Diabetes Data Group criteria, the number needed to treat was 14 for cesarean delivery, 20 for gestational hypertension or preeclampsia, 40 for shoulder dystocia, 14 for large for gestational age, and 12 for macrosomia.

"In summary, women diagnosed with mild GDM by the less stringent Carpenter-Coustan criteria and by the stricter National Diabetes Data Group criteria both benefit from nutritional counseling, dietary therapy, and insulin when indicated," the authors conclude.

Dr Valent added that both studies emphasize the importance of treating hyperglycemia. "As Mom's blood glucose increases, there's a strong association with increasing birthweight even for lower cutoff ranges," she said. "If we're conservative, we'll have the opportunity to reach more women."

Aside from the rare but catastrophic potential outcome of stillbirth for those born to mothers with GDM, the more immediate risk is that mother and baby are separated as the newborn is transferred to the neonatal intensive care unit to be treated for low blood sugar or jaundice, Dr Valent said. Further, "one of the most important risks we are getting more and more information about is the developmental programed risk for the baby under the care of a woman with diabetes," Dr Valent added. "There's an increasing risk of obesity in childhood and diabetes and heart disease later in life."

Study limitations included the fact that both studies were conducted in the United Kingdom, and therefore may not generalizable to American pregnancies; the use of secondary analysis in the second study; and the reliance on blood sugar alone when lipids or fats in mothers' blood may be a bigger driver of bigger babies, Dr Valent said.

The research for the study by Dr Sovio and colleagues was funded by the National Institute for Health Research Cambridge Comprehensive Biomedical Research Centre and the Stillbirth and Neonatal Death Charity, and GE donated two Voluson i ultrasound systems for the study. One coauthor serves on a Medtronic scientific advisor board. Another coauthor has received research support from GE, Roche, and GlaxoSmithKline and has received payments for advisory board attendance at GSK and Roche and consultancy for GSK and is also inventor of a patent submitted by GSK related to preterm birth prevention. The research for the study by Dr Harper and colleagues was funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development, General Clinical Research Centers Grant, and the National Center for Research Resources. The authors have disclosed no relevant financial relationships. Dr Valent has disclosed no relevant financial relationships.

Diabetes Care. Published online April 7, 2016. Abstract

Obstet Gynecol. Published online April 4, 2016. Abstract

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