"High prepregnancy HbA1c is challenging to improve and affects insulin requirements, gestational length, and...

The aim of this study was to explore how prepregnancy glycosylated hemoglobin (HbA1c) affects the course of HbA1c and insulin requirements during pregnancy, the gestational length, and birthweight.

An observational cohort study was conducted consisting of 380 women with type 1 diabetes who gave birth 530 times from 2004 to 2014. The participants were divided into four groups according to prepregnancy HbA1c.

HbA1c was significantly different between the groups at all time intervals from week 5 to 10 to week 33 to 36 (P ≤ .01). In group 1, with the lowest prepregnancy HbA1c (<6.5% [48 mmol/mol]), HbA1c stayed at the same level throughout pregnancy. In the other groups (group 2: 6.5% [48 mmol/mol]-7.9% [63 mmol/mol], group 3: 8% [64 mmol/mol]-9.9% [86 mmol/mol], and group 4: > 10% [86 mmol/mol]) a decrease in HbA1c was seen in early pregnancy but stabilized from midpregnancy onward. Group 1 had the lowest daily insulin requirements throughout pregnancy among the four groups (P = .001). The relationship between birthweight and prepregnancy HbA1c was found to be inversely U-shaped. Mean gestational length in group 4 was significantly shorter than in group 1 (P = .001).

In this very large cohort, we found that a poor prepregnancy HbA1c is a predictor for poor glycemic control during pregnancy and that HbA1c decreases until midpregnancy and then plateaus. A very poor prepregnancy HbA1c is associated with shorter gestational length and lower birthweight, which is contrary to the common assumption that poor glycemic control leads to higher birthweight.