New study shows closed-loop insulin delivery significantly improves pregnancy glucose control

An international randomized clinical trial has shown that closed-loop insulin delivery improves glycemic control during pregnancy for individuals with type 1 diabetes, according to findings published in JAMA and summarized in a new announcement from the University of Calgary. The system, also referred to as automated insulin delivery (AID), uses algorithm-driven real-time insulin adjustments to help maintain glucose within a pregnancy–specific target range.^1,2

“For pregnant women with type 1 diabetes, keeping glucose within a healthy range is very important to the health of the woman and fetus,” said Lois Donovan, MD, co–principal investigator. The news release explained that AID “mimics a healthy pancreas” by adjusting insulin dosing according to current and predicted glucose levels.

The CIRCUIT trial enrolled pregnant individuals with type 1 diabetes across 14 sites in Canada and Australia before 14 weeks of gestation. Participants were randomly assigned to the Tandem t:slim X2 insulin pump with Control-IQ technology or to standard insulin therapy using multiple daily injections or open-loop pumps. Continuous glucose monitoring was used in both groups. The primary analysis included 88 participants.

How much did the closed-loop system improve pregnancy glucose control?

The primary outcome was the percentage of time spent in the pregnancy-specific glucose range of 63–140 mg/dL between 16 and 34 weeks of gestation. The closed-loop group had 65.4% time in range, compared with 50.3% in the standard care group—an adjusted difference of 12.5 percentage points (95% CI, 9.5–15.6; P < .001).

This equates to approximately 3 additional hours per day in the target range.

“These results will help inform people who are pregnant or planning pregnancy regarding the benefits of this AID system,” said co–principal investigator Denice Feig, MD.

How did AID affect hyperglycemia, hypoglycemia, and glycemic variability?

Secondary outcomes also favored closed-loop therapy:

• Less time above 140 mg/dL (difference −11.5 percentage points)
• Less time below 63 mg/dL (difference −1.0 percentage points)
• Lower mean glucose (−10.7 mg/dL)
• Reduced glycemic variability

These improvements began immediately after system initiation and were consistent across sites and baseline HbA_1c strata.

Did closed-loop therapy influence maternal outcomes?

Although not powered for pregnancy outcomes, exploratory maternal findings included the following:

• Lower HbA_1c at 24 and 34 weeks of gestation
• Lower rate of preeclampsia (13.6% vs 25.0%)
• Similar rates of preterm birth between groups

The total daily insulin dose was lower in the closed-loop group in post hoc analysis.

What were the neonatal outcomes?

Neonatal outcomes were largely comparable, as follows:

• Preterm birth <37 weeks: 27.3% (closed loop) vs 29.5% (standard care)
• Neonatal hypoglycemia requiring treatment: 43.2% in each group
• NICU admission ≥1 day: 31.8% (closed loop) vs 27.3% (standard care)

Neonatal hyperbilirubinemia was more common in the closed-loop group, whereas shoulder dystocia was less frequent.

Were there safety concerns with closed-loop insulin delivery?

Safety outcomes included the following:

• One severe hypoglycemia episode during pregnancy in the closed-loop group
• Two diabetic ketoacidosis episodes in the closed-loop group and one in the standard care group
• Device-related adverse events in the closed-loop group; none serious

Overall, the system was deemed safe during pregnancy.

What is the clinical significance for pregnant individuals with type 1 diabetes?

The University of Calgary emphasized that “every 72-minute per day increase, with glucose in the desired range during pregnancy, is associated with a reduction in newborn complications.” The trial’s 3-hour daily improvement exceeds this threshold, highlighting the clinical importance of closed-loop systems during pregnancy.¹

While some prior trials of other systems have shown mixed results, the CIRCUIT trial supports the use of the Tandem Control-IQ system during pregnancy when available.

Conclusion

The closed-loop insulin delivery system significantly improved time in the pregnancy-specific glucose range compared with standard therapy. These findings support consideration of closed-loop technology for pregnant individuals with type 1 diabetes when accessible.

References

1. Improving health during pregnancy for those with type 1 diabetes. News release. University of Calgary. November 13, 2025. Accessed November 19, 2025. https://www.eurekalert.org/news-releases/1105978
2. Donovan LE, Lemieux P, Dunlop AD, et al; CIRCUIT Collaborative Group. Closed-loop insulin delivery in type 1 diabetes in pregnancy. JAMA. Published online October 24, 2025. doi:10.1001/jama.2025.19578