Anemia is a major cause of morbidity and mortality during pregnancy in developing countries. The main aim of this study was to determine the prevalence and effect of nutritional status in the form of anemia and associated factors among pregnant women on infant birth weight attending ANC of Gajendra Narayan Singh Sagarmatha Zonal Hospital of Rajbiraj, Saptari. The study was observational and the design was a cross sectional prospective survey involving 150 pregnant women aged 15-49 years. Structured questionnaire and records from maternal health record books including body weight and haemoglobin levels were used for the assessment. The major findings from the study indicated that 91.2% of women did not gain the recommended weight during second trimester of pregnancy. Mean weight gain during second trimester was 2.2± 2.1kg. Also 95.3% did not gain the recommended weight in their third trimester. Mean weight at third trimester was 2.9± 2.2kg. The prevalence of anaemia at first, second and third trimesters were 63.2%, 80.7% and 88.7% respectively. Mean haemoglobin levels at first, second and third trimesters were 10.4± 1.8g/dl; 6.1± 1.6g/dl; and 9.9± 1g/dl respectively.