Figure 1 Forced expiratory volume in 1 s (FEV₁) in litres at age 31 years by tertiles of birth weight and weight gain during the first year in (A) men and (B) women in the 1966 Northern Finland Birth Cohort study. The figure shows mean values and 95% confidence limits. Values obtained from regression models and adjusted for gestational age at birth, maternal smoking during pregnancy and factors at 31 years: height, weight, cigarette smoking (never, former and current), and physical activity level (high versus low); p value for interaction between birth weight and weight gain during the first year was 0.88 in men and 0.04 in women.