Closed-Loop Insulin Delivery during Pregnancy in Women with Type 1 Diabetes

Published - Written by Rebecca Berger, M.D.

A 32-year-old woman with type 1 diabetes mellitus presents to your office. She is 8 weeks pregnant. Her blood sugar has been well controlled on a standard insulin pump, but she understands that blood sugar can be more difficult to control during pregnancy.  You have previously discussed the importance of tight glucose control in pregnancy to reduce the risk of complications such as neonatal death, preterm birth, and macrosomia. Your patient has heard about new advances in insulin delivery with closed-loop technology and wants to know if she is a candidate for this technology.

Closed-loop insulin systems use continuous glucose monitors (CGMs) to measure glucose in real time and a computer algorithm to adjust insulin-pump delivery, requiring less input from the patient than a standard insulin pump for daily management of insulin dosing. Studies of this technology in supervised outpatient settings and in the community have shown better glycemic control than with standard insulin pumps, but none of the studies included pregnant women.

A study published in this week’s NEJM addresses the effectiveness and safety of closed-loop insulin delivery in pregnancy. In a 4-week overnight, randomized, crossover study, followed by a 14-week feasibility study, 20 pregnant women (enrolled between 8 and 24 weeks gestation) with a diagnosis of type 1 diabetes and treated with insulin, were randomized to receive insulin treatment with either the closed-loop system (intervention) or a sensor-augmented pump (control), and then crossed over to the other system. After the crossover study and a 2-week washout, patients chose either the closed-loop system or sensor-augmented pump for use day and night through labor, delivery, and the postpartum period (feasibility phase).

The overnight closed-loop system delivered insulin via pump every 12 minutes based on a computer algorithm that calculates insulin doses using CGM. The sensor-augmented pump also uses CGM but requires patient involvement to calculate insulin dosing. Among the 16 patients who completed the crossover study, the primary outcome — the proportion of time with overnight glucose levels within target range (62–140 mg/dL) — was significantly greater during closed-loop treatment than during the control treatment (74.7% vs. 59.5%; P= 0.002). Closed-loop delivery was also associated with significantly lower mean glucose and rate of maternal hyperglycemia. The percentage of time spent hypoglycemic in both groups was low (<2.0%) and did not differ significantly.

During the 14-week feasibility phase, 14 participants chose to continue with the closed-loop device. During this phase, the women using the closed-loop technology had target glucose levels for a mean of 69% of the time; during the 24 hours before delivery, they had target levels for 87% of the time, and continued to have low rates of hypoglycemia.

The investigators conclude that overnight closed-loop therapy resulted in a significant increase in time spent within the glucose target range for pregnancy, without increasing the incidence of hypoglycemia. Despite daily and weekly changes in insulin pharmacokinetics during pregnancy, the system appeared to be safe through the antepartum, labor and delivery, and postpartum periods. Although small, this study provides important data to support the safety of the new closed-loop technology in pregnant women.

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Rebecca is a 2016-2017 NEJM Editorial Fellow and a hospitalist at Massachusetts General Hospital. She graduated from Columbia University College of Physicians and Surgeons in 2013 and completed internal medicine residency at Massachusetts General Hospital in 2016. Her interests include medical education, quality improvement, patient safety, health care delivery innovation, and teaching value in health care.

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