Objective To evaluate the interaction between different subtypes of gestational diabetes mellitus (GDM) and insulin level on newborn birth weight, and provide evidence for the management of GDM.

Methods A prospective cohort study design was used, and the pregnant women who met the inclusion criteria were selected by using the register in Zhoushan Women and Children's Hospital from January 2022 to May 2023, the information about the socio-demographic characteristics, marital status and childbearing history, dietary pattern and nutritional status of pregnant women were collected, and oral glucose tolerance test was conducted for the pregnant women in the second trimester, their fasting insulin levels were detected, and the information about neonatal growth and development were collected in follow up. Linear regression model was used to analyze the association between insulin level and birth weight. Multinomial logistic regression model was used to analyze the association of insulin level with low birth weight and macrosomia. Pregnant women were grouped according to GDM definition and the association between insulin level and birth weight within the groups were analyzed. The interaction between GDM subtype and insulin resistance on birth weight was investigated by crossover analysis.

Results  After adjusting for maternal age, gestational week, gravidity and parity, maternal insulin level and insulin resistance were positively correlated with newborn birth weight (insulin level: β=3.01±1.21, P=0.013; Insulin resistance index: β=14.99±5.24, P=0.004); After further adjustment of pre-pregnancy BMI and pregnancy weight gain, insulin secretion was negatively correlated with birth weight (β=−0.06±0.03, P=0.046). After grouping according to GDM definition, similar results were found only in non-GDM pregnant women. High insulin level (≥75.00%) and insulin resistance (≥75.00%) were positively correlated with the incidence of macrosomia high insulin level: OR=2.03, 95%CI:1.08–3.83, P=0.028; Insulin resistance: OR=3.69, 95%CI:1.91–5.95, P=0.002. No interaction between GDM subtype and insulin resistance status on birth weight was found (P_interaction>0.05).

Conclusion Insulin resistance level, insulin secretion level and overall insulin level of pregnant women have important effects on newborn birth weight. More attention should be paid to the different insulin indicators, especially insulin resistance index, and more targeted pregnancy management guidelines based on the GDM subtypes should be developed.