Does the 1-step method of gestational diabetes mellitus screening improve pregnancy outcomes?

BACKGROUND Despite considerate debate, the best method of diagnosing gestational diabetes mellitus remains unknown. A commonly used method of gestational diabetes mellitus screening in the United States is the 2-step method, which includes screening with a 50-gram, 1-hour glucose challenge followed by a 100-gram, 3-hour diagnostic oral glucose tolerance test. The International Association of Diabetes and Pregnancy Study Group has recommended the 1-step method using a 75-gram, 2-hour oral glucose tolerance test. The International Association of Diabetes and Pregnancy Study Group thresholds have been predicted to increase the rates of gestational diabetes mellitus, yet little is known about the effect on pregnancy outcomes, especially in the United States. OBJECTIVE This study aimed to determine whether adoption of the 1-step method of gestational diabetes mellitus screening leads to improved obstetrical outcomes at a single academic institution. STUDY DESIGN This is a retrospective cohort study of patients who delivered before and after a switch from the 2-step method to the 1-step International Association of Diabetes and Pregnancy Study Group method in July 2015. Women with a due date of January 1, 2012 through October 1, 2015 were diagnosed with gestational diabetes mellitus using the 2-step method with Carpenter and Coustan criteria. After a 6-month transition period, outcomes from women with a due date of May 1, 2016 through February 1, 2018, when the 1-step International Association of Diabetes and Pregnancy Study Group criteria were used to diagnose gestational diabetes mellitus, were evaluated. Women with gestational diabetes mellitus were managed similarly throughout the study period. The primary outcome was the incidence of primary cesarean delivery. Maternal and neonatal outcomes were compared using chi-square and t tests, and multivariable logistic regression was used to control for changes in the population. RESULTS With the adoption of the International Association of Diabetes and Pregnancy Study Group method, the rates of gestational diabetes mellitus more than doubled, to 23.3% from 9.2% (P<.001). The rates of primary cesarean delivery increased with the International Association of Diabetes and Pregnancy Study Group criteria (22.2% vs 19.4%, P=.001), and the incidence of shoulder dystocia was not significantly different (1.1% vs 0.8%, P=.07). The rate of preeclampsia decreased during the time the 1-step method was in use (8.2% vs 10.9%, P<.001). The rate of macrosomia was not different using a definition of ≥4500 g (0.99% vs 0.86%, P=.5) but was reduced when using a definition of ≥4000 g (8.0% vs 6.0%, P<.001). The rate of neonatal intensive care unit admission did not change significantly. Controlling for maternal age, body mass index, race or ethnicity, chronic hypertension, and parity, the adjusted odds of a diagnosis of gestational diabetes mellitus increased 3-fold (adjusted odds ratio, 3.3; 95% confidence interval, 2.90-3.66) with 1-step testing, the adjusted odds of a shoulder dystocia increased (adjusted odds ratio, 1.48; 95% confidence interval, 0.97-2.25), and the adjusted odds of preeclampsia decreased (adjusted odds ratio, 0.64; 95% confidence interval, 0.55-0.74). There was no change in the adjusted odds of primary cesarean delivery (adjusted odds ratio, 1.05; 95% confidence interval, 0.94-1.17). CONCLUSION Although the rates of gestational diabetes mellitus increased 3-fold with the adoption of the International Association of Diabetes and Pregnancy Study Group method, the rates of primary cesarean delivery, shoulder dystocia, and birthweight ≥4500 g did not decrease in our population. The incidence of preeclampsia decreased; our analysis suggests that this was not because of the increased diagnosis of gestational diabetes mellitus. In our patient population, a large increase in the rates of gestational diabetes mellitus did not lead to an improvement in several clinically meaningful obstetrical outcomes.