Background: Obesity would increase the possibility of unfavorable effects on maternal and fetal outcomes. So, it is important to investigate the relationship between maternal obesity and its possible effects and determinants. Subject & Methods: A cohort study was conducted on 104 pregnant women at the 3rd trimester attending antenatal clinic of zagazig university hospital for routine antenatal care. Data was collected by semi-structured interview, follow up sheet in the 3rd trimester, as well as labor, and delivery sheets and neonatal assessment sheet. Results: Findings of the study revealed that, women aged ≥ 30 years old tend to be obese (p = 0.005). Multipara has 3 times risk of obesity (Relative risk (RR) = 3.0, 95 % Confidence Interval (CI) = 2.27-15.0) than primipara. Obese women had 2 times risk to have miscarriage than non-obese (RR =2.2, 95 % CI = 1.18-8.21). Obese pregnant women were liable to pregnancy complication such as gestational hypertension, gestational diabetes and preeclampsia (p = 0.03). Also they had 6 times risk to have cesarean delivery (RR =5.5, 95 % CI = 1.17-3.55) than non-obese women. Fetal macrosomia are more common among babies born to obese mothers (p < /p>