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Objective: Continuous glucose monitoring (CGM) provides far greater detail about fetal exposure to maternal glucose across the 24 hour day. Our aim was to examine the role of temporal glucose variation on the development of large for gestational age infants (LGA) in women with treated gestational diabetes (GDM). Research Design and Methods: A prospective observational study of 162 pregnant women with GDM in specialist multidisciplinary antenatal diabetes clinics. Participants undertook a 7-day masked CGM at 30-32 weeks gestation. Standard summary indices and glycemic variability measures of CGM were calculated. Functional data analysis was applied to determine differences in temporal glucose profiles. LGA was defined as birth weight ≥90th percentile adjusted for infant sex, gestational age, maternal BMI, ethnicity and parity. Results - Mean glucose was significantly higher in women who delivered an LGA infant (6.2 vs 5.8 mmol/l P=0.025 or 111.6 mg/dl vs 104.4 mg/dl respectively). There were no significant differences in percentage time in, above or below the target glucose range, or in glucose variability measures (all P>0.05). Functional data analysis revealed that the higher mean glucose was driven by a significantly higher glucose for 6 hours overnight (00h30-06h30) in mothers of LGA infants (6.0 ± 1.0 mmol/l vs 5.5 ± 0.8 mmol/l p=0.005; 108.0 ± 18.0 mg/dl vs 99.0 ± 14.4 mg/dl respectively). Conclusions: Mothers of LGA infants run significantly higher glucose overnight compared to mothers without LGA. Detecting and addressing nocturnal glucose control may help to further reduce rates of LGA in women with GDM.