Abstract:The aim of this study was to evaluate the values of hematological parameters at different trimesters of pregnancy in pregnant women who attended antenatal care at Sabratha Teaching Hospital, Northwest Libya. This cross-sectional survey included consecutive pregnant women who attended the obstetrical department in Sabratha Teaching Hospital for prenatal booking. This study was carried out over period of 6 month from April 2016 to September 2016. The study involved 120 pregnant women as the study group and 40 non-pregnant women as control. The study pregnant women were between the ages of 18 to 45 years. 5 ml of venous blood samples were taken from each pregnant woman in K 3 -EDTA tubes for the haematological examinations. The analysis of haematological indices was done using automated hematological analyzer. The obtained results showed that the mean age of pregnant women was 30 years ± 5.8 SD, 48.4% of pregnant women were between 21-30 years old, 40.8% were at age between 31-40 years. The most prevalent blood group in pregnant women was group O, 47.5%; followed by blood group A, 28.3%; blood group B, 17.5% and blood group AB, 6.7%. 15.8% of the pregnant women were observed to lack Rh antigen in their blood. Highly significance decrease in Hb, Hct, MCH, MCHC, lymphocytes%, RBCs and blood platelets count and significant decrease in MCV as compared with non pregnant women. On the other hand, highly significance increased in WBCs count, and neutrophils % of pregnant women compared with non pregnant women. A progressive decline in Hb concentration and haematocrite values from the first to third trimester was observed. The mean corpuscular volume was significantly decreased in the second trimester. The values of MCH showed highly significant decrease in the second and third trimester, and MCHC decreased significantly in the first trimester. WBC count and neutrophils % showed highly significant increase from the first to the third trimester. Lymphocytes % were highly significant decreased from the first to the third trimester. Mixed percentage of leukocytes (eosinophil, basophil and monocytes) decreased significantly in the third trimester. Platelets count exhibited a highly significant decrease in the second and third trimesters, and a significantly decrease in the first trimester. It can be concluded that a significant changes in the haematological parameters at different trimesters of pregnancy in pregnant women. So it is essential to monitor and manage these parameters during pregnancy.