HMN 2025: How Closed-loop insulin system improves glucose control during pregnancy

A collaborative effort across 14 clinical centers in Canada and Australia reports that pregnant women with type 1 diabetes using a closed-loop insulin system spent more time in the pregnancy-specific glucose range than those receiving standard care.

Pregnant women with type 1 diabetes face high rates of adverse outcomes linked to hyperglycemia. Narrow glycemic targets during pregnancy create added difficulty for patients and care teams.

Previous studies outside of pregnancy have found that closed-loop insulin systems reduce hyperglycemia and hypoglycemia. In a closed-loop insulin system, there is an automated insulin-delivery setup that continuously adjusts insulin dosing based on real-time glucose readings. Limited testing of closed-loop systems during pregnancy has left outcomes of the widely available option unclear.

In the study, “Closed-Loop Insulin Delivery in Type 1 Diabetes in Pregnancy: The CIRCUIT Randomized Clinical Trial,” published in JAMA, researchers designed an open-label randomized clinical trial to assess the efficacy of a closed-loop system in pregnancy.

A total of 88 participants were randomized in the primary analysis. Participants were assigned 1:1 to closed-loop therapy or standard care with continuous glucose monitoring.

Closed-loop participants used the Tandem t:slim X2 pump hosting Control-IQ technology with pregnancy-directed setting recommendations. Primary outcome measured the percentage of time in the pregnancy-specific glucose range of 63 to 140 mg/dL from 16 to 34 weeks’ gestation.

Primary glycemic outcome

Closed-loop therapy achieved 65.4% time in the pregnancy-specific glucose range of 63–140 mg/dL from 16 to 34 weeks’ gestation, compared with 50.3% with standard care. Consistency across intention-to-treat, per-protocol, and sensitivity analyses was reported, with similar effect estimates over the same gestational window.

Secondary glycemic measures

An immediate improvement after closed-loop initiation was observed. Participants experienced lower glycemic variability and fewer mild or moderate hypoglycemic events. Time above 140 mg/dL was 11.5 percentage points lower with closed-loop. Time below 63 mg/dL was 1.0 percentage point lower and mean glucose was 10.7 mg/dL lower.

Exploratory maternal outcomes

HbA1c was lower in the closed-loop group at 24 weeks by 0.49% and at 34 weeks by 0.43%. Fewer participants had preeclampsia, 13.6% vs. 25.0%. The total daily insulin dose was lower in a post hoc analysis. Rates of cesarean delivery and preterm birth were similar across groups.

Neonatal findings

Shoulder dystocia occurred in 6.8% of closed-loop births and 15.9% of standard care births. Shoulder dystocia is known to be more common in pregnancies with diabetes as these infants tend to have proportionally larger shoulders, chest, and abdominal circumferences for their weight.

Neonatal hyperbilirubinemia and intensive care admissions ?1 day were more frequent in the closed-loop group.

Authors conclude that pregnant women with type 1 diabetes using this closed-loop system spent significantly more time in the pregnancy-specific glucose range than those receiving standard care. Findings support use of this system in pregnancy.

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