<b><i>Background/Aims:</i></b> Carbohydrate counting (CC) is a helpful strategy for the treatment of type 1 diabetes mellitus (T1DM) and the main parameters used in this method are the insulin to carbohydrate ratio (ICR) and the sensitivity factor (SF). Throughout pregnancy, a state of insulin resistance develops. Therefore, we hypothesized that ICR and SF change and our aim was to describe the pattern of modification of these parameters in pregnant women with T1DM on CC. <b><i>Methods:</i></b> This study followed 21 women with T1DM throughout pregnancy. Starting ICR was 1:15 and SF was calculated using the formula: 1,500/total daily insulin dose (TDID; for regular insulin) or 1,800/TDID (for ultra-rapid analogs). ICR was adjusted every 1-2 weeks according to self-monitoring of blood glucose. SF was recalculated every 1-2 weeks. <b><i>Results:</i></b> Throughout gestation there was a mean decrease in the ICR in breakfast, lunch and dinner of 8.2 (<i>p</i> < 0.0001), 7.7 (<i>p</i> = 0.003) and 7 (<i>p</i> = 0.005) grams per international units (g/IU), respectively. Mean SF reduction from first to third trimester was 10 mg/dL per IU (mg/dL/IU; <i>p</i> < 0.0001). <b><i>Conclusions:</i></b> Women with T1DM in CC during pregnancy evolve with a progressive reduction in the ICR at every meal (mean of 8.2 g/IU for breakfast, 7.7 g/IU for lunch and 7 g/IU for dinner) and also in the SF (10 mg/dL/IU).