Introduction: Studying on the changes of hematology system in pregnant women was interested by researchers in the world. Objective: to describe some characteristics of CBC and blood coagulation tests in first trimester pregnant women. Subjects and method: 77 pregnant women from 5 to14 week managed by Hanoi Obstetrics and Gynecology Hospital (study group) and 29 healthy women aged 15-49 (control group). The research parameters were platelet count, PT, APTT, plasma fibrinogen concentration, RBC, Hb, Hct, MCV, MCH, MCHC, WBC. Results: Platelet count of study group was 223.27 + or - 45.70 G/I, APTTs was 26.54 + or - 2.10s, rAPTT was 0.95 + or - 0.08, PTs was 11.45 + or - 0.67s, PT percent was 91.74 + or - 9.95 percent, PT-INR was 1.05 + or - 0.07, and plasma fibrinogen concentration was 3.51 + or - 0.79 g/I. RBC was 4.19 + or - 0.38 T/I, Hb concentration was 120.60 + or - 8.22 g/l, Hct was 0.36 + or - 0.03 I/I, MCV was 86.03 + or - 5.66 fl, MCH was 28.98 + or - 2.00 pg, MCHC was 336.92 + or - 9.52 g/l, WBC was 9.09 + or - 2.19 G/I. Conclusion: Except to PTs, the remaining coagulation parameters changed significantly in comparision with control group while no significant differences about CBC between two groups.