Fetal malformations in women with pregestational diabetes mellitus based on pre-pregnancy fasting plasma glucose levels

To evaluate the risk of fetal malformation in pregnant women with pregestational diabetes mellitus based on pre-pregnancy fasting plasma glucose (FPG) levels. This cohort study used the Korean Health Insurance Review and Assessment (HIRA) database, including 5,687 women with pre-pregnancy diabetes and FPG measurements within one year before conception. Subjects were grouped into three glycemic level categories: low (FPG < 100 mg/dL [< 5.5 mmol/L]), moderate (FPG: 100–125 mg/dL [5.6–6.9 mmol/L]), and high (FPG ≥ 126 mg/dL [≥ 7.0 mmol/L]). The low glycemic group was divided into four subgroups based on FPG levels. The relative risks of fetal malformations were calculated using multivariable analysis compared to a reference group (FPG < 84 mg/dL [< 4.7 mmol/L]). Fetal malformation rates were 10% in the low, 13.6% in the moderate, and 18.6% in the high glycemic groups (P < 0.001). Teratogenic risks were 1.3 times higher in the moderate glycemic group and 1.8 times higher in the high glycemic group compared to the reference group. The high glycemic group had 2.5 times greater risk of cardiac malformations and 3.3 times greater risk of skeletal malformations. Preconceptional FPG levels ≥ 100 mg/dL [≥ 5.5 mmol/L] in women with pregestational diabetes elevate the risk of fetal malformations, especially cardiac and skeletal malformations at FPG levels ≥ 126 mg/dL [≥ 7.0 mmol/L].