Closed-loop insulin system improves blood sugar control during pregnancy in those with type 1 diabetes

The findings, published in JAMA, offer promising evidence for improving maternal and fetal outcomes in a high-risk population. 

“Keeping blood glucose in the optimal range for pregnancy is exceptionally challenging when someone has type 1 diabetes, despite their best efforts and the support of dedicated health care clinics,” says Dr. Denice Feig, an endocrinologist and clinician scientist at Sinai Health’s Lunenfeld-Tanenbaum Research Institute and a co-principal investigator of the study. Dr. Feig is also Head of the Diabetes and Endocrinology in Pregnancy Program at Mount Sinai Hospital.

Pregnancy adds extra challenges because blood sugar targets are much tighter to protect both mother and baby. Individuals with type 1 diabetes during pregnancy have a higher likelihood of miscarriage and preeclampsia, a serious condition marked by dangerously high blood pressure. Furthermore, their babies are more prone to being excessively large or premature, experiencing low blood sugar at birth, and facing an increased risk of birth defects.

The CIRCUIT trial compared a hybrid closed-loop (HCL) insulin therapy using the Tandem t:slim X2 insulin pump with Control-IQ technology to standard insulin injections or non-automated pumps, both with continuous glucose monitoring. The system, which mimics a healthy pancreas, automatically adjusts insulin levels in real time based on current and predicted glucose readings.

Participants using the closed-loop system spent an average of 65.4% of time in the desired glucose range, compared to 50.3% in the standard care group – a statistically significant difference of 12.5 percentage points. This translates to approximately three additional hours per day in the target range, which is a critical improvement linked to reduced newborn complications.

“This is very important because we have learned from other larger studies that every 72-minute per day increase in time spent in the desired glucose range during pregnancy is associated with better outcomes for newborns,” says Dr. Lois Donovan, endocrinologist and the other co-principal investigator from the University of Calgary.

The study also showed other benefits, such as lower average blood sugar, more stable blood sugar levels, and fewer episodes of low blood sugar. Importantly, the system was well tolerated, with no serious device-related adverse events reported.

The trial involved 14 sites across Canada and Australia, with the University of Calgary as the lead site and included clinics in Toronto, including Mount Sinai Hospital and Sunnybrook, Vancouver, Quebec City, London (Ont.), Winnipeg, Halifax, Canberra, Melbourne, and Sydney. 

The improvement in glucose control was immediate and sustained throughout pregnancy.

“This finding will help inform people who are pregnant or planning pregnancy regarding the benefits of this AID system, which can help them achieve better glucose levels in pregnancy and hopefully better pregnancy outcomes” said Dr. Feig, who is also a professor of Medicine at the University of Toronto.

Funding for the study was provided by Diabetes Canada, MSI Foundation, the University of Calgary Clinical Research Fund, the Buckley Family Trust, and the Mount Sinai Department of Medicine Research Fund.