CGM in Type 2, GDM
CGM in type 2 diabetes in pregnancy was addressed in a recently published systematic review and meta-analysis, which found only three qualifying randomized controlled trials and concluded that CGM use was not associated with improvements in perinatal outcomes, as assessed by LGA and preeclampsia (Am J Obstet Gynecol MFM. 2023;5:100969). “It’s very limited by the small sample size and the fact that most [patients] were using intermittent CGM,” Dr. Durnwald said. “It highlights how important it is to perform larger studies with continuous CGM.”
While the 2024 ADA standards say there are insufficient data to support the use of CGM in all patients with type 2 diabetes or GDM — and that the decision should be individualized “based on treatment regimen, circumstance, preferences, and needs” — real-world access to CGM for type 2, and even a bit for GDM, is improving, she said.
Some insurers require patients to be on insulin, but the trends are such that “we certainly talk about CGM to all our patients with type 2 diabetes and even our patients with GDM,” Dr. Durnwald said in a later interview. “CGMs are being advertised so we definitely have people who ask about them upon diagnosis, and we try to make it work for them.”
Is Preventing Maternal Hypoglycemia Possible?
Advancements in technology and pharmacology aimed at optimizing glycemic control — increased adoption of CGM, the use of insulin pump therapy, and the use of more rapid insulin analogs — appear to have had little to no impact on rates of severe maternal hypoglycemia in type 1 diabetes in pregnancy, said Dr. Rosenn, referring to several published studies.
The CONCEPTT study in type 1 diabetes, for instance, “gave us the best data we have on the use of CGM,” but differences in the percentage of patients with severe hypoglycemia and the total number of severe hypoglycemia episodes were basically the same whether patients used CGM or not, he said.
Closed-loop insulin delivery systems have been found in nonpregnant patients with type 1 diabetes to “be helpful in keeping people in range and also possibly [decreasing nocturnal hypoglycemia],” but the systems are not approved for use in pregnancy. “There’s not enough data on use in pregnancy, but probably more important, the algorithms used in the closed-loop systems are not directed to the targets we consider ideal for pregnancy,” Dr. Rosenn said.
In a pilot study of a closed-loop delivery system customized for pregnancies complicated by type 1 diabetes, 10 pregnant women were recruited at 14-32 weeks and, after a 1- to 2-week run-in period using a regular CGM-augmented pump, they used the closed-loop system targeting a daytime glucose of 80-110 mg/dL and nocturnal glucose of 80-100 mg/dL.
Mean TIR (a target range of 63-140 mg/dL) increased from 65% during the run-in period to 79% on the closed-loop system, and there were significant decreases in both time above range and time in the hypoglycemic ranges of < 63 mg/dL and < 54 mg/dL. Hypoglycemic events per week (defined as < 54 mg/dL for over 15 minutes) decreased from 4 to 0.7 (Diabetes Care. 2023;46:1425-31).
The investigators are continuing their research, and there are currently two randomized controlled trials underway examining use of closed-loop systems designed for pregnancy, said Dr. Rosenn, who was involved in feasibility research leading up to the pilot study. “So I’m hopeful we’ll see some encouraging information in the future.”
Maternal hypoglycemia during pregnancy is more common in type 1 diabetes, but it also affects pregnancies complicated by type 2 diabetes and GDM. In addition to the strict glycemic control imposed to improve maternal and fetal outcomes, pregnancy itself plays a role.
Research several decades ago from the Diabetes in Pregnancy Program Project, a prospective cohort in Cincinnati which Dr. Rosenn co-led, documented impaired counterregulatory physiology in pregnancy. Even in nondiabetic patients, there are declines in secretion of glucagon and growth hormone in response to hypoglycemia, for instance. In patients with type 1 diabetes, the diminishment in counterregulatory response is more severe.