Fasting blood glucose as a screening measure for late-onset gestational diabetes in the third trimester.

Objective: To investigate the positive rate of late-onset gestational diabetes mellitus (GDM) by additional fasting blood glucose (FBG) screening at 32-34 gestational weeks (GW) and analyse the perinatal outcomes of late-onset GDM after standard treatment.
Design: An Prospective cohort study.
Setting: Single centre in China.
Population: 1130 singleton pregnancies with negative GDM screening in their first and second trimester.
Methods: Additional FBG testing was performed at 32-34 GW. Pregnancies with FBG ≥5.1 mmol/L were diagnosed as GDM and received standardized treatment. Perinatal outcomes were collected and compared.
Main Outcome Measures: Diagnosis of late-onset GDM, obstetric and neonatal outcomes.
Results: 6.3% (71/1130) of participants had FBG values ≥5.1 mmol/L and were diagnosed with late-onset GDM. Sixty-five (91.5%) were treated by dietary therapy and 6 (8.5%) by insulin therapy. The perinatal outcomes of full-term delivery were compared. The incidence of macrosomia (22.7% vs. 5.1%, adjusted odds ratio (aOR) 5.51, 95% confidence interval (CI) 1.83-16.61, p = 0.002) and NICU transferring (18.3% vs. 10.1%, aOR 1.94, 95% CI 1.01-3.74, p = 0.046) was significantly higher in late-onset GDM group than that in FBG <5.1 mmol/L group. Elevated FBG was associated with overweight or obesity during pregnancy (54.9% vs. 34.9%, OR 2.27, 95% CI 1.40-3.68, p = 0.001).
Conclusions: 6.3% of singleton pregnancies with normal GDM screening results in the first and second trimester were found to have late-onset GDM by additional FBG screening at 32-34 GW, and their risk of macrosomia during a full-term pregnancy remains significantly higher after standard treatment.
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