Pregnancy is associated with normal physiological changes that assist fetal survival as well as preparation for labour. It is typically broken into three trimesters, each of about three months. These distinctions are useful in describing the changes that take place over time. Biochemical parameters reflect these adaptive changes are clearly distinct from the non-pregnant state. The mother and the placenta produces many hormones, maternal thyroid function during pregnancy is important for both the mother and the developing fetus. Especially during the first trimester, when the fetus is completely dependent on the mother for thyroid hormone. It also decreases maternal tissue sensitivity to insulin, resulting in gestational diabetes. Dilution anaemia is caused by the rise in plasma volume, Blood volume increases by 40% in the first two trimesters this causes low level of albumin . This is just to an increase in plasma volume through increased aldosterone. Increase liver metabolism is also seen, with increased gluconeogenesis to increase maternal glucose levels .Renal plasma flow increases during pregnancy. Objectives :1-This Study includes measurement of the thyroid hormones T3,T4,TSH and biochemical parameters(glucose, uric acid, total protein ,lipid profile , and hemoglobin) in serum of pregnant women during the three trimesters and serum of non-pregnant women. 2- Investigation the relationship between thyroid hormones level and bio- chemical tests profile in serum of the pregnants during three trimesters and also non-pregnant women. Subject and Methods :In the present study the individual sera of hormones (triiodothyronin (T3 ) , thyroxin (T4) and thyroid -stimulating hormone (TSH) were assayed in 70 healthy women . Serum collected from fifty pregnant women at three trimesters and twenty non-pregnant women as a control group. The measurements occurs in both Al- ELWIA Hospital and Central Public Health Laboratories. The T3,T4 and TSH was measured by using Immunophlorences method by miniVidas. This measurement is recruited from 1/7/2007 to 8/4/2008. This study also designed to investigate changes in the levels of biochemical parameters (Glucose, Uric acid ,Total protein, Lipid profile , and Hemoglobin )in sera of pregnant women at three trimesters and on sera of non-pregnant women. The glucose, uric acid, lipid profile were measured by spectrophotometer instrument .The Total protein was measured by using Clinical refractometers instrumental ( ATAGO) and hemoglobin was measured by Micro-Haematocrit Centrifuge instrument .. Results :Results of pregnant women at first trimester showed that there was a significant difference (P<0.001) in hormones T4 compared with control group . Results in the second trimester it was found that a highly significant difference (P<0.001)in hormones T3,T4 and TSH (P<0.05) compared with the control group .In the third trimester there was a significant differennce (P<0.001) in hormones T4 and T3 (P<0.05) compared with the control group. The results of Biochemical parameters showed that at the first trimester there was a positive significant difference (P<0.001) in glucose, hemoglobin compared with control group ,In the second trimester there was a positive significant difference (P<0.05) in cholesterol , LDL and hemoglobin , and in the third trimester it was found apositive significant differences (P<0.001) in Total protein, cholesterol , triglyceride , LDL and VLDL compared with the control group. A strong positive correlation coefficient was found between T3 at the firsttrimister with a weak of gestation and HDL, and a negative correlation coefficient between T3 with glucose and uric acid . And a significant positive correlation coefficient was found at the second trimester between T3 with triglyceride, VLDL and CHO/HDL, while a negative correlation with uric acid ,total protein and hemoglobin . A positive correlation was found at third trimester between T3 with glucose and uric acid. Results of non-pregnant group were found with a negative correlation coefficient between T3 with triglyceride, VLDL, LDL ,and LDL/HDL. There was a negative correlation coefficient between T4 at the firsttrimister with glucose . Results At the second trimester there was a positive correlation coefficient between T4 with weak of gestation and T3,there was a negative correlation coefficient between T4 with total protein .Results At third trimester there was a negative correlation coefficient between T4 with triglyceride and VLDL.Results in non-pregnant state there was a negative correlation coefficient between T4 with hemoglubin. There was a positive correlation coefficient between TSH at the firsttrimister with glucose, uric acid, cholesterol, VLDL, triglyceride, LDL, CHO/HDL and LDL/HDL .Results At the second trimester there was a positive correlation coefficient between TSH with glucose, and uric acid ,there was a negative correlation coefficient between TSH with triglyceride, VLDL and T3 . Results At third trimester there was a positive correlation coefficient between TSH with glucose. Results in non-pregnant state there was a positive correlation coefficient between TSH with HDL, and T3 . Conclusions: 1-In this study it was an increasing in higher T3 and T4 levels and decreasing in the TSH levels in serum of pregnant at the three trimesters which will produced hyperthyroidism if not controlled symptoms. 2- The study proves that changes in biochemical parameters in serum pregnant during three trimester , affects on the mother and fetal. 3- There were a relationships between thyroid hormone and biochemical parameters for pregnant women and non-pregnant women.