Individual linear regression models, stratified by BMI category, showed first trimester leptin and first trimester TNFα were significantly associated with birthweight, but only in normal weight women (Normal weight: leptin B = .007 95%CI: .002, .011, p = 0.005 and TNFα B = -14.99 95%CI: -29.43,-0.543, p = 0.042; Overweight/Obesity: leptin B = .002, 95%CI: -.005, .009, p = 0.531 and TNFα B = 1.09, 95%CI: -20.35, 22.54, p = 0.918). The gene discussed is TNF; the disease is obesity due to melanocortin 4 receptor deficiency.