Maternal glucose level and body mass index measured at gestational diabetes mellitus screening and the risk of macrosomia: results from a perinatal cohort study

Objective: To examine the impact of maternal blood glucose (BG) level and body mass index (BMI) measured at gestational diabetes mellitus (GDM) screening on the risk of macrosomia. Design: A perinatal cohort of women were followed up from receiving perinatal healthcare to giving birth. Setting: Beichen District, Tianjin, China between June 2011 and October 2012. Participants: 1951 women aged 19-42 years with valid values of BMI and BG level at GDM screening (24-28 weeks gestation), singleton birth and birth weight (BW)>2500 g. Main outcomes and measures: Primary outcome was macrosomia (BW>4000 g). BG level and BMI were measured at GDM screening. Results: 191 (9.7%) newborns were macrosomia. The ORs (95% CIs) of macrosomia from multiple logistic regression were 1.14 (1.10 to 1.19, p<0.0001) for BMI and 1.11 (1.01 to 1.23, p=0.03) for BG. When BMI and BG levels (continuous) were modelled simultaneously, the OR for BMI was similar, but significantly attenuated for BG. Areas of receiver operating characteristics (ROC) were 0.6530 (0.6258 to 0.6803) for BMI and 0.5548 (0.5248 to 0.5848) for BG (chi(2)=26.17, p<0.0001). BG (mmol/L, <6.7, 6.7-7.8 or >= 7.8) and BMI in quintiles (Q1-Q5) were evaluated with BG <6.7 and Q2 BMI as the reference group. The ORs of macrosomia were not statistically different for mothers in Q1 or Q2 of BMI regardless of the BG levels; the ORs for >= Q3 of BMI were elevated significantly with the highest OR observed in Q5 of BMI and BG levels >= 7.8 (6.93 (2.61 to 18.43), p<0.0001). Conclusions: High BMI measured at GDM screening was the most important determinant for risk of macrosomia. These findings suggest that GDM screening may be a critical gestational time point to initiate maternal weight control oriented intervention strategy to lower the risk.