Highlights
Adjunctive flash glucose monitoring in gestational diabetes mellitus did not improve time-in-range glycemic outcomes compared to standard self-monitoring of blood glucose alone. Infants born to mothers using flash glucose monitoring showed a significantly lower incidence of large-for-gestational-age (3% vs 11%, p=0.05). The unexpected primary outcome finding and the promising secondary neonatal outcome highlight the need for larger confirmatory trials before widespread adoption in this population.
Background
Gestational diabetes mellitus (GDM) affects approximately 14% of pregnancies globally, with prevalence rising in tandem with increasing maternal obesity and advanced parental age. The condition confers substantial short- and long-term risks for both mother and offspring, including hypertensive disorders of pregnancy, operative delivery, and neonatal macrosomia. Large-for-gestational-age (LGA) infants—defined as birth weight above the 90th percentile for gestational age—represent one of the most clinically meaningful adverse outcomes, associated with birth trauma, metabolic complications, and elevated childhood obesity risk.
Self-monitoring of blood glucose (SMBG) has long served as the cornerstone of glycemic assessment in GDM, enabling patients and clinicians to titrate dietary intake and pharmacotherapy in real time. However, SMBG provides only intermittent snapshots of glucose dynamics, potentially missing postprandial excursions or nocturnal hypoglycemia. Continuous glucose monitoring (CGM), and more recently flash glucose monitoring (FGM), offer the promise of comprehensive glucose profiles with reduced patient burden. Despite widespread adoption in type 1 and type 2 diabetes, the incremental value of these technologies in GDM remains insufficiently characterized.
The study by Zorko and colleagues addresses this evidence gap, investigating whether adjunctive FGM improves glycemic metrics and, more importantly, hard clinical endpoints in pregnant women with GDM.
Study Design
This was an open-label, single-center, randomized controlled trial conducted at a tertiary care center in Slovenia. Participants were pregnant women diagnosed with GDM according to local criteria, recruited at a median gestational age of 27 weeks. The study randomized 205 women in a 1:1 ratio to either adjunctive FGM plus SMBG (n=102) or SMBG alone (n=103).
Women in the FGM arm wore the Abbott FreeStyle Libre flash glucose sensor, which measures interstitial glucose every 15 minutes and provides ambulatory glucose profiles upon sensor scanning. Both groups performed SMBG using standard capillary glucose meters, with measurement frequency determined by clinical protocols. Glycemic targets aligned with established GDM recommendations: fasting glucose below 5.3 mmol/L and 1-hour postprandial glucose below 7.8 mmol/L.
The prespecified primary outcome was the percentage of SMBG measurements within the established target range. Secondary outcomes encompassed maternal glycemic parameters (fasting, preprandial, and postprandial glucose concentrations) and neonatal outcomes, including the incidence of LGA infants, macrosomia, neonatal hypoglycemia, and composite adverse outcomes. Analyses followed the intention-to-treat principle, and all statistical comparisons used two-sided tests with alpha set at 0.05.
Key Findings
The study population had a median age of 32 years and a median pre-pregnancy BMI of 23.5 kg/m², reflecting a relatively low-risk cohort with well-controlled glycemia at baseline. Notably, the primary glycemic outcome did not favor the FGM arm.
Primary Outcome: Time-in-Range
Contrary to expectations, the percentage of SMBG measurements within the target range was significantly lower in the adjunctive FGM group compared to the SMBG-only group (89.5% vs 92.6%, p=0.04). This counterintuitive finding suggests that awareness of continuous glucose data did not translate into improved glycemic control through the SMBG platform, at least in this population with already favorable glycemic profiles.
Secondary Maternal Outcomes
Median fasting and 1-hour postprandial self-monitored glucose concentrations were comparable between groups and remained within recommended targets throughout the study period. No significant differences were observed in the proportion of women requiring insulin therapy or in glycemic variability indices between arms.
Neonatal Outcomes: A Promising Signal
The most clinically significant finding emerged in the secondary neonatal endpoint: the incidence of large-for-gestational-age infants was substantially lower in the FGM group (3% vs 11%; p=0.05; odds ratio 0.27, 95% confidence interval 0.07–0.99). This represents a 73% reduction in odds, though the absolute difference (8 percentage points) reflects a number-needed-to-treat of approximately 12.5 women to prevent one case of LGA.
While these findings are compelling, the authors appropriately caution that this was a secondary outcome assessed in a relatively small sample, with only 14 total LGA events across both arms. The 95% confidence interval, though statistically significant, spans a wide range (0.07–0.99), indicating substantial uncertainty around the true effect size. Additional secondary neonatal outcomes, including rates of macrosomia, neonatal hypoglycemia, and NICU admission, did not differ significantly between groups, though the study was not powered for these individual comparisons.
Expert Commentary
The discordance between the primary glycemic endpoint and the neonatal outcome raises important physiological and methodological considerations. One plausible explanation is that FGM captured subtle glycemic patterns—particularly postprandial excursions and time-in-range metrics—that SMBG failed to detect, even though the latter served as the primary endpoint. If FGM enabled more nuanced dietary counseling or insulin titration adjustments not reflected in SMBG-derived metrics, this could explain improved fetal growth trajectories without apparent differences in the proportion of SMBG readings within range.
The study population—predominantly women with well-controlled GDM and relatively low BMI—may not fully represent the higher-risk pregnancies where intensified monitoring might yield greater benefits. In women with more severe hyperglycemia or obesity, the incremental value of FGM could be more pronounced. Conversely, the already excellent glycemic control in both arms may represent a ceiling effect, limiting the potential for FGM to further improve outcomes.
Several limitations warrant acknowledgment. The open-label design introduces potential ascertainment bias, particularly for neonatal outcomes assessed by clinicians aware of maternal allocation. The single-center nature of the trial may limit generalizability to other settings with different patient characteristics or care models. The number of outcome events was small, precluding robust subgroup analyses or definitive conclusions about effect modification by baseline severity, BMI, or gestational age at randomization. Additionally, the study utilized SMBG as the reference standard for the primary endpoint, whereas many contemporary GDM trials incorporate CGM-derived metrics such as time-in-range, time-above-range, and glycemic variability indices.
Current clinical guidelines from the American College of Obstetricians and Gynecologists (ACOG) and the International Association of Diabetes and Pregnancy Study Groups (IADPSG) do not endorse routine CGM or FGM for GDM, citing insufficient evidence. The findings of Zorko et al. do not yet justify a paradigm shift, but they generate a compelling hypothesis warranting investigation in adequately powered, multicenter trials with prespecified neonatal primary endpoints.
Conclusion
In this randomized trial of 205 women with gestational diabetes, adjunctive flash glucose monitoring did not improve the primary endpoint of SMBG-derived time-in-range compared to standard monitoring alone. However, the device was associated with a statistically significant and clinically meaningful reduction in large-for-gestational-age neonates—a secondary finding that should be interpreted cautiously given the sample size, number of events, and multiplicity of testing.
For practicing obstetricians and maternal-fetal medicine specialists, the current evidence does not support routine FGM adoption in all GDM pregnancies. However, the signal toward improved neonatal outcomes is intriguing and may justify selective use in well-resourced settings or in women with difficulty achieving glycemic targets. Large-scale, adequately powered trials with clinically meaningful primary endpoints are needed to definitively establish the role of continuous and flash glucose monitoring technologies in gestational diabetes management.
Funding and ClinicalTrials.gov
This study received institutional support. The trial was registered at ClinicalTrials.gov (NCT identifier pending verification against original publication). The authors reported no conflicts of interest relevant to this study.
References
1. Zorko K, Munda A, Janež A, Pongrac Barlovič D. Flash glucose monitoring addition to self-monitoring of blood glucose and perinatal outcomes in gestational diabetes: a randomized controlled trial. Am J Obstet Gynecol. 2026 Apr 2. PMID: 41935728.
2. International Association of Diabetes and Pregnancy Study Groups Consensus Panel. International Association of Diabetes and Pregnancy Study Groups recommendations on the diagnosis and classification of hyperglycemia in pregnancy. Diabetes Care. 2010;33(3):676-682.
3. American College of Obstetricians and Gynecologists. Practice Bulletin No. 190: Gestational Diabetes Mellitus. Obstet Gynecol. 2018;131(2):e49-e64.
