In Norway, there were parallel increases and subsequent decreases in birth weight (BW) and consumption of sugar-sweetened carbonated soft drinks (SSC) during the period 1990-2010, and by an ecological approach, we have suggested that the relationship was causal. The objective of this study was to examine if such a relationship was present in a prospectively followed cohort of pregnant women. The study population included 62,494 term singleton mother-infant dyads in the Norwegian Mother and Child Cohort Study (MoBa), a national prospective cohort study in Norway from 1999 to 2008. The association between SSC consumption and BW was assessed using multiple regression analyses with adjustment for potential confounders. Each 100 ml intake of SSC was associated with a 7.8 g (95% confidence interval [CI]: -10.3 to -5.3) decrease in BW, a decreased risk of BW > 4,500 g (odds ratio [OR]: 0.94, 95% CI: 0.90 to 0.97) and a near significantly increased risk of BW 4,500 g (OR: 1.18, 95% CI: 1.00 to 1.39) and a trend towards significant increase in mean BW (25.1 g, 95% CI: -2.0 to 52.2) per 100 ml SSC. Our findings suggest that increasing consumption of rapidly absorbed sugar from SSC had opposite associations with BW in normal pregnancies and pregnancies complicated by gestational diabetes mellitus.