Biochemical changes in women with gestational diabetes mellitus (GDM) and healthy pregnant women (HPW) were studied. 103 GDM women and 97 HPW were selected and registered for the study from the admitted pregnant women of Gynea Ward of Khyber Teaching Hospital, Peshawar. Sociodemographic and other pregnancy related information, including monthly-income, age, body mass index (BMI), parity, previous history of gestational diabetes and family history of diabetes, were collected on a well-designed questionnaire. Fasting blood sugar (FBS), random blood sugar (RBS), glycosylated hemoglobin (HbA1c), hemoglobin (Hb), platelet count (PC), total cholesterol (TC), triglycerides (TG), high density lipoprotein-cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C), liver function tests namely alanine amino transferase (ALT), alkaline phosphatase (ALP), serum bilirubin, renal function tests namely urea, creatinine, and hormones like insulin, prolactin, cortisol, triiodothyronine (T3), thyroxin (T4) and thyroid stimulating hormone (TSH) were determined by standard procedures using recommended kit for each procedure. The data were statistically analyzed using computer software, SPSS version 10. The mean monthly income of GDM and HPW was Rs.30845 ± 11107 vs Rs.28360 ± 11511, mean age was 34.01 ± 4.54 years vs 30.30 ± 5.86 years, mean BMI was 28.07 ± 2.90 kg/m 2 vs 27.30 ± 1.94 kg/ m 2 , mean parity was 5.44 ± 2.49 vs 4.95 ± 2.43, mean systolic BP was 114.80 ± 17.14 mm Hg vs 107.70 ± 19.40 mm Hg and mean diastolic BP was 86.50 ± 7.48 mm Hg vs 80.70 ± 10.02 mm Hg respectively. Age, BMI, systolic and diastolic BP was significantly higher (P<0.05) according to Pearson Chi- square test in GDM women as vicompared to HPW. The mean FBS, RBS and HbA1c of GDM women and HPW were 111.69 ± 8.70 mg/dL vs 86.59 ± 6.91, 145.45 ± 6.62 mg/dL vs 123.52 ± 9.37mg/dL and 6.58 ± 1.30 vs 4.95 ± 0.45 respectively. The FBS, RBS and HbA1c of GDM women were significantly higher than the HPW (P<0.001). The mean Hb concentration and PC of GDM women and HPW were 10.98 ± 1.12% vs 11.01 ± 1.03% and 226.31 thousand/mL vs 228.14 ± 37.61 thousand/mL. In lipid profile TC and TG of GDM group were significantly higher than the contol group (P<0.01). The mean TC of GDM and HPW was 206.01 ± 18.79 mg/dL vs 195.01 ± 24.15 mg/dL, TG was 190.12 ± 19.83 mg/dL vs 172.13 ± 21.66 mg/dL, HDL-C was 55.21 ± 8.20 mg/dL vs 56.20 ± 8.82 mg/dL and LDL-C was 93.13 ± 18.71 mg/dL vs 88.10 ± 16.36 mg/dL respectively. Liver and renal function tests of GDM women were not significantly different (P<0.05) from HPW. In liver function tests the mean ALT, ALP and serum bilirubin values of GDM women were 30.21 ± 12.47 U/L, 190.55 ± 22.20 U/L, 0.67 ± 0.41 mg/dL while of HPW were 29.64 ± 7.96 U/L, 189.95 ± 21.28 U/L, 0.58 ± 0.17 mg/dL respectively. In renal function tests the mean serum urea and serum creatinine values of GDM women were 23.70 ± 8.54 mg/dL and 0.82 ± 0.32 mg/dL while of HPW were 21.97 ± 6.16 mg/dL and 0.74 ± 0.15 mg/dL respectively. The mean insulin level of GDM women were 33.68 ± 3.69 μIU/mL, which was significantly higher (P<0.01) than the mean insulin level of HPW (29.80 ± 2.80 μIU/mL ). Among placental hormones the mean prolactin values of GDM women and HPW were 135.47 ± 9.83 ng/mL vs 131.80 ± 8.54 ng/mL and mean serum cortisol values were 734.9 ± 51.1 ng/mL vs 719.2 ± 54.7 ng/mL. The mean serum prolactin and serum cortisol values of GDM women were significantly higher (P< 0.05) when compared to HPW. No significant differences were viiobserved in the concentration of thyroid hormones. The mean TSH values of GDM and HPW were 1.72 ± 0.95 mlU/L vs 1.87 ± 0.83 mlU/L, mean T 3 values were 2.51 ± 0.62 nmol/L vs 2.62 ± 0.57 nmol/L, mean T 4 values were 103. 86 ± 14.74 nmol/L vs 105.38 ± 13.93 nmol/L. Cesarean sections (P=0.009), still birth rate (P=0.003) and macrosomic babies (P=0.001) were significantly more in GDM group.