Earlier Diagnosis of Gestational Diabetes Is Linked to Preterm Birth

The timing of the diagnosis of gestational diabetes mellitus (GDM) is significantly associated with preterm delivery.

Women who received a diagnosis of GDM before 24 weeks’ gestation were 10 times more likely to deliver before 37 weeks’ gestation than women who received a GDM diagnosis after 24 weeks’ gestation, according to new research presented April 29, 2014, in the poster session at ACOG’s 2014 Annual Clinical Meeting in Chicago.

Between 2% and 10% of all pregnancies are complicated by GDM, and up to 60% of women with GDM will have type 2 diabetes mellitus within 10 to 20 years after delivery. Most women are screened for GDM between 24 and 28 weeks’ gestation. Current recommendations from ACOG suggest earlier screening for GDM (before 24 weeks’ gestation) is appropriate only for women with certain risk factors, such as a history of GDM, known impaired glucose metabolism, or obesity.

However, the protocol at Montefiore Medical Center, the University Hospital for Albert Einstein College of Medicine, Bronx, NY, is to screen every woman for GDM during her first prenatal visit regardless of the length of pregnancy. The screening protocol involves an initial glucose challenge test, followed by a glucose tolerance test if the former test is positive. If this initial screening occurred before 24 weeks’ gestation and was negative, the patient is screened again after 24 weeks’ gestation.

Ivan Ngai, MD, who presented the poster, explained, “In our institution, we decided to screen for diabetes earlier because of the high incidence of obesity and lack of primary care within our patient population (the Bronx).”

In a retrospective review of electronic medical records from 2008 to 2013, Ngai and colleagues identified women with a diagnosis of GDM and created study groups based on the timing of GDM diagnosis-before 24 weeks’ gestation (n=305) and after 24 weeks’ gestation (n=401). Both groups contained similar numbers of obese patients. Patients in the earlier-diagnosis group were slightly older than those in the later-diagnosis group (mean age, 32.9 y vs 31.1 y, respectively).

When evaluating pregnancy outcomes, Ngai and colleagues found that women with a diagnosis of GDM before 24 weeks’ gestation, compared with those with a diagnosis of GDM after 24 weeks’ gestation, were significantly more likely to deliver before 37 weeks’ gestation (20% vs 11.4%, respectively) and more likely to deliver before 34 weeks’ gestation (8.9% vs 2.0%, respectively). The rates of cesarean delivery, preeclampsia, fetal demise, shoulder dystocia, and macrosomia (body weight > 4000) were similar between groups.

Regression analysis, however, showed that diagnosis of GDM before 24 weeks was the only independent predictor of delivery before 37 weeks’ gestation, with an odds ratio of 10.40 (P<0.001).

“Patients with a diagnosis of gestational diabetes before 24 weeks were 10 times more likely to deliver preterm. That’s huge,” said Ngai in an interview with ObGyn.net.

The clinical significance of these findings is that there seems to be a subset of women with poorer pregnancy outcomes that may be related to an unknown history of glucose intolerance, pre-diabetes, or uncontrolled diabetes.

Gestational diabetes occurs because the placenta creates hormones, such as estrogen, cortisol, and human placental lactogen, that makes insulin less effective, explained Ngai. “Since there isn’t much placenta in the beginning of a pregnancy, how much can the placenta actually affect insulin levels in a woman who screened positive at 8 weeks’ gestation? Since any diagnosis of diabetes in pregnancy is, by definition, gestational diabetes, these women have gestational diabetes. However, it isn’t a stretch to think that some of these women who screened positive very early in their pregnancy may have had undiagnosed diabetes before becoming pregnant.”

“For high-risk populations, such as obese patients or those with previous gestational diabetes, patients should be screened at their first prenatal visit. And if they do screen positive early in their pregnancy, perhaps these patients should be considered even more high risk than the typical patient with gestational diabetes,” suggested Ngai.