High pre-pregnancy HbA1c is challenging to improve and affects insulin requirements, gestational length and birth weight".

BACKGROUND The aim of this study was to explore how pre-pregnancy HbA1c affects the course of HbA1c and insulin requirements during pregnancy, the gestational length and birth weight METHOD: 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 4 groups according to pre-pregnancy HbA1c. RESULTS HbA1c was significantly different between the groups at all time-intervals from week 5-10 to week 33-36 (p ≤ 0.01). In Group 1, with the lowest pre-pregnancy HbA1c (  10% (86 mmol/mol)) a decrease in HbA1c was seen in early pregnancy but stabilized from mid-pregnancy onwards. Group 1 had the lowest daily insulin requirements throughout pregnancy among the four groups (p = 0.001). The relationship between birth weight and pre-pregnancy HbA1c was found to be inversely U-shaped. Mean gestational length in Group 4 was significantly shorter than Group 1 (p = 0.001). CONCLUSIONS In this very large cohort, we found that a poor pre-pregnancy HbA1c is a predictor for poor glycemic control during pregnancy and that HbA1c decreases until mid-pregnancy and then plateaus. A very poor pre-pregnancy HbA1c is associated with shorter gestational length and lower birth weight, which is contrary to the common assumption that poor glycemic control leads to higher birth weight. HIGHLIGHTS In this very large cohort of 530 pregnancies in women with T1DM, we found that a high pre-pregnancy HbA1c is a predictor for sub-optimal glycemic control during pregnancy and that HbA1c only decreases until mid-pregnancy and then plateaus. In addition, a very high pre-pregnancy HbA1c is associated with shorter gestational length and lower birth weight Z-score, which is contrary to the common assumption of poor glycemic control leading to higher birth weight.