Aim The aim of this study was to examine the safety of insulin glargine during pregnancy in women with type 1 diabetes mellitus (T1DM). Methods This retrospective multicentre study involved women with T1DM treated with insulin glargine before conception and throughout pregnancy. The main investigated parameters were HbA 1c during the first and third trimesters, major congenital malformations, and perinatal mortality and complications. Results For the 102 women with T1DM in the study, HbA 1c during the first and third trimesters was 6.7 ± 1.2% (95% CI 6.4–6.9%) and 6.2 ± 0.9% (95% CI 6.0–6.4%), respectively. Two congenital malformations (2%) were reported, and one stillbirth (1%) occurred at week 35 of gestation. The rate of preterm delivery was 23%. The mean birth weight was 3381 ± 595 g (95% CI 3255–3506 g), and the proportion of large-for-gestational-age infants was 30%. Conclusion Insulin glargine use throughout pregnancy does not appear to be associated with an increased rate of severe congenital malformations.