INTRODUCTION Pregnancy in women with type 1 diabetes mellitus (T1DM) is associated with higher risk of complications. Strict glycemic control before conception reduces the risk of unfavorable outcomes. OBJECTIVES The aim of the study was to assess changes in clinical characteristics, preconception treatment, and glycemic control of women with T1DM at the first antinatal visit. PATIENTS AND METHODS We analyzed the records from the first antenatal visit of 524 women with T1DM in the years 1998-2012. The follow‑up period was divided into 3 5‑year periods. RESULTS Differences in the age of patients between the 3 follow‑up periods were observed (28.2 ±5.7 years for 1998-2002; 27.3 ±4.5 years for 2003-2007; and 29.4 ±4.8 years for 2008-2012; P <0.0001). The number of women planning pregnancy did not change and reached 32.1% in the first, 44.4% in the second, and 40.4% in the third period (P = 0.2). The use of rapid‑acting insulin analogues increased from 2.6% to 46.5% and then to 95.6% (P <0.001). The rate of therapy with personal insulin pumps before pregnancy increased from 4.6% in the first, through 23.5% in the second, to 33.3% in the third period (P <0.001). Over the subsequent periods, we observed a decrease in hemoglobin A1c (HbA1c) levels at the first antenatal visit (from 7.4% ±1.6%, through 6.9% ±1.4%, to 7.0% ±1.4%; P = 0.06), as well as a decrease in HbA1c levels between the subgroups of women planning pregnancy (6.8% ±1.4%, 6.6% ±1.2%, and 6.1% ±0.8%, P = 0.015). CONCLUSIONS In the years 1998-2012, an increase in the use of insulin analogues and personal insulin pumps by women with T1DM before conception was observed, and these changes were accompanied by a slight improvement in glycemic control, particularly among women planning pregnancy. The percentage of women planning pregnancy did not change during the follow‑up.