Background: Large for gestational age (LGA) birthweight is a common complication of gestational diabetes mellitus (GDM). However, it is unclear how much of this risk is explained by antenatal hyperglycaemia versus other maternal factors.

Aim: To identify the impact of glycaemic control on LGA in GDM pregnancies.

Methods: A retrospective analysis of GDM women (ADIPS2014 criteria) at Bankstown-Lidcombe Hospital May 2019-December 2022 was conducted. Multiple pregnancies, non-livebirths, and births at other hospitals were excluded. Variables collected included maternal age, gravida/parity, BMI, ethnicity, gestational weight gain according to Institute of Medicine (IOM) targets, gestational age at diagnosis and delivery, mode of delivery, OGTT results, HbA1c and self-monitored blood glucose (SMBG) levels at each patient’s first, second, and last visit to clinic. Women were treated to capillary glucose targets: fasting<5.3mmol/L, 1hr<7.4mmol/L and 2hr<7.0mmol/L. Cases were grouped by the presence or absence of LGA (defined as birthweight >90th centile). Variables significant on univariate analyses (p<0.05) were included in a logistic regression. Crude and adjusted odds ratios were calculated. SPSS version 27 was used for analyses.

Results: There were a total of 810 women diagnosed with GDM during the study period. LGA was present in 117 (14.4%) live births. Greater than 30% SMBG above target range at first (OR 1.67, 95%CI 1.13-2.48) and last visits (OR 2.92, 95%CI 1.60-5.38) were significantly associated with an increased risk of LGA. Other maternal factors associated with LGA on univariate analyses included overweight, fasting glucose ≥5.3mmol/L on OGTT, HbA1c ≥5.5%, multiparity, history of macrosomia, and caesarean section. Lower risk of LGA was seen in East/South-East Asian ethnicity (OR 0.47, 95%CI 0.28-0.80).

On multivariate analysis, >30% elevated SMBG readings at first and last visits were no longer significantly associated with an increased rate of LGA. Maternal factors which remained predictors of LGA included a prior history of macrosomia (aOR 3.39, 95%CI 1,76-6.54), exceeding total recommended gestational weight gain by IOM criteria at first visit to GDM service (aOR 2.28, 95%CI 1.43-3.62), delivery via caesarean section (aOR 2.00, 95%CI 1.30-3.09), fasting glucose ≥5.3mmol/L on OGTT (aOR 1.75, 95%CI 1.12-2.75), and multiparity (aOR 1.66, 95%CI 1.06-2.60) (see figure 1).

Figure 1: Significant risk factors for LGA on multivariate analysis.

Conclusion: In this cohort, prior history of macrosomia conferred the highest risk of LGA. While treating to glycaemic targets is important in GDM pregnancies, non-glycaemic factors also influence the risk of LGA.