Happy Holidays to all, and to celebrate the season we have a very sweet triple episode release today! The first two episodes are focused on the pathophysiology, diagnosis, and treatment of GDM, while the third is a special interview with Dr. Donald Coustan, Professor and Chair Emeritus of the Department of Obstetrics and Gynecology at Brown University. Dr. Coustan was recently profiled by AJOG as a “Giant in Obstetrics and Gynecology.” We hope you enjoy the interview and his perspective on GDM and OB-GYN more generally.
We discuss multiple ways to diagnose GDM, based on different organization’s recommendations. The classic Carpenter-Coustan criteria endorsed by ACOG and the National Diabetes Data Group (NDDG) are based on two-step testing. An initial 50 gram glucose tolerance test is performed, and patients move on to the second screen if their 1hr glucose is measured at 130-140 mg/dL, pending on the institution. It is generally accepted that a value >200 mg/dL is diagnostic without moving on to the second step.
The three hour test is based on a 100g glucose load. The cutoffs vary by time point. Two elevated values are needed to diagnose GDM; however, there is increased risk for the patient even with just one elevated value on three hour testing. The classic Carpenter-Coustan criteria as well as the NDDG criteria are shown here from PB 190:
There is also single-step testing proposed by the International Association for the Study of Diabetes in Pregnancy, that uses a 75g, two-hour glucose tolerance test. Any one elevated value (fasting > 92, 1 hour > 180, or 2 hour > 153) is diagnostic of GDM, and no second screen is needed. The ADA has endorsed these criteria recently but also admits that there is not clear-cut evidence to support one screening strategy over another. ACOG endorses the two-step screening at this time.
Much of the research regarding treatment of GDM that we review in the podcast is well-reviewed in PB 190, so we won’t rehash it here. If non-pharmacologic treatments fail (monitored fasting and postprandial blood glucose levels are consistently elevated), an oral agent or insulin is required, with insulin being the gold-standard. How do you initiate insulin? See our guide below!
And remember — postpartum patients with GDM need a 2 hour, 75 gram glucose tolerance test between 4 and 12 weeks postpartum to rule out type 2 diabetes. A fasting > 125 or a 2 hour > 200 is diagnostic. A fasting between 100-125 or a 2 hour between 140-199 demonstrates impaired glucose tolerance. And even with normal values, anyone with GDM has a 15-70% chance of developing T2DM later in life, so it’s an important part of the pregnancy history to correspond back to the patient’s PCP.