ObjectiveTo describe the immunological and hematological reference intervals of low-risk pregnant women.MethodsA cross-sectional retrospective database analysis of a basic and translational study analyzing the hematological evaluation blood counts and immunophenotyping of TCD3 + , TCD4 + , TCD8 + , B, and natural killer (NK) cells of the peripheral blood in 79 low-risk pregnant women and of 30 control women from the state of Pernambuco, Brazil, was performed.ResultsNo significant differences were detected between the hematological profiles of the 2ndand 3rdtrimesters. Nevertheless, the median level of B cells decreased significantly in the 2nd(174 × 103µL;p< 0.002) and 3rdtrimesters (160 × 103µL;p< 0.001), compared with the control group (296 × 103µL). Similarly, the median level of NK cells was lower in the 2nd(134 × 103µL;p< 0.0004) and 3rdtrimesters (100 × 103µL,p< 0.0004), compared with the control group (183 × 103µL). In contrast, relative TCD4+ and TCD8+ levels increased in the 2ndand 3rdtrimesters compared with the controls (TCD4 + : 2ndtrimester = 59%;p< 0.001; 3rdtrimester = 57%;p< 0.01; control = 50%; and TCD8 + : 2ndtrimester = 31%;p< 0.001; 3rdtrimester = 36%;p< 0.01; control = 24%).ConclusionLow-risk pregnant women have ∼ 40% less B and NK cells in the peripheral blood, compared with non-pregnant women. These parameters may improve health assistance for mothers and contribute to define reference values for normal pregnancies.