Continuous glucose monitoring in pregnancies with type 1 diabetes: small increases in time-in-range improve maternal and perinatal outcomes

BACKGROUND:Continuous glucose monitors (CGM) provide detailed information regarding glycemic control in pregnant patients with type 1 diabetes (T1D). Little data have been published examining the association between CGM parameters and perinatal outcomes among gravidas with T1D using CGM. OBJECTIVE:To examine the association between perinatal outcomes and time-in-range (TIR) as assessed by CGM used in pregnant individuals with T1D. We hypothesized that higher TIR would be associated with lower risk of adverse perinatal outcomes. STUDY DESIGN:This multicenter retrospective cohort study included all gravidas with T1D using CGM who delivered in 2020-2022 at 5 University of California sites. Only those with CGM target range set to 70-140 mg/dL (±10 mg/dL) were included. TIR (%) was recorded at 12, 16, 20, 24, 28, and 32 weeks. The primary maternal and neonatal outcomes were preeclampsia and large for gestational age (LGA), defined as birthweight (BW) ≥ 95th percentile. Kruskal-Wallis tests were used to compared median TIR in those with and without the primary outcomes. Log-binomial regression was used to obtain risk ratios, with adjustment for microvascular disease and years with T1D. RESULTS:A total of 91 patients were included. Most used an insulin pump (81%) and did not have diabetic microvascular disease (72%). Median time since diagnosis of T1D was 16 years, and median periconception A1c was 6.7%. Compared to those with preeclampsia, normotensive gravidas had significantly higher TIR at nearly every time point. A similar pattern was seen for those with normal BW infants compared to LGA infants. On adjusted analyses, every 5-unit increase in TIR at 12 weeks was associated with a 45% and 46% reduction in the risk of preeclampsia and LGA, respectively (ARR 0.55, 95% CI 0.30-0.99 for preeclampsia; ARR 0.54, 95% CI 0.29-0.99 for LGA). CONCLUSIONS:Higher TIR is associated with lower risk of preeclampsia and LGA. This association is seen early in gestation, when each 5-unit increase in TIR is associated with ∼50% reduction in the risk of these complications. These findings can be used to counsel patients regarding risk of pregnancy complications at specific TIR values and to encourage patients that even small improvements in TIR can have significant impact on pregnancy outcomes. Larger studies are needed to further explore these findings and to identify optimal TIR to reduce perinatal complication rates.