Background/aim: Diabetes mellitus is associated with an increased risk for neonatal morbidity and mortality. One of the most important goals in treating pregnancies complicated with diabetes is keeping glucose level within the normal range, especially in the first trimester. A portable insulin pump for continuous subcutaneous insulin infusion (CSII) represents the best form of therapy for patients with type 1 diabetes mellitus during pregnancy. The aim of our study was to evaluate the effects of therapy with a portable insulin pump for continuous subcutaneous insulin infusion during the first trimester of pregnancy on the quality of glycoregulation and pregnancy outcome in women with type 1 diabetes mellitus. Methods. A total of 17 newly diagnosed pregnant women with type 1 diabetes mellitus were treated with CSII therapy for three months. The parameters of glycoregulation (hemoglobin A, glycosylated - HbA1c, mean blood glucose value in daily profiles - MBG, daily requirement for insulin - IJ/kg BM), lipid levels, blood pressure and renal function were estimated before and after the therapy. These parameters were correlated with parameters of pregnancy outcome: fetal weight, APGAR score, duration of pregnancy. Results. There was a significant improvement in HbA1c (8.94±1.62 vs. 6.90±1.22 %, p < 0.05), MBG (9.23±2.22 vs. 6.41±1.72 mmol/l, p < 0.01), and daily requirement for insulin (0.66±0.22 vs. 0.55±0.13 IJ/kg BM, p < 0.05) during the CSII therapy. There were significant correlations between fetal weight and HbA1c (r = -0.60, p < 0.05), triglyceride levels (r = −0.63, p < 0.01), and the number of pregnancies (r = −0.62, p < 0.01), as well as between APGAR score and MBG (r = −0.52, p < 0.05) and cholesterol levels (r = −0.65, p < 0,01) before a portable insulin pump was applicated. Conclusions. There was a significant improvement in the quality of glycoregulation during CSII therapy in the pregnant women with type 1 diabetes mellitus. The quality of glycoregulation in the moment of conception was the important factor for pregnancy outcome.