Background We hypothesized that women with congenital heart disease (CHD) are at increased risk of giving birth preterm, including very and moderately preterm and giving birth to infants small for gestational age (SGA). We aimed to investigate this in a nation-wide study with focus on the potential modifying effect of socioeconomic status. Methods and Results We performed a cohort study using Danish nation-wide registers between 1997 and 2014. The exposure, maternal CHD, was subdivided into simple, moderate and complex based on severity of defects. Outcomes were preterm birth and SGA. Cox regression was used to estimate hazard ratios (HR). A total of 933 149 births including 3745 births among women with CHD were studied. The risk of giving birth preterm and SGA were higher among women with CHD as compared with women without CHD; for example, adjusted hazard ratios of preterm birth according to severity: simple 1.33 (95% CI, 1.11-1.59), moderate 1.45 (95% CI, 1.14-1.83) and complex 3.26 (95% CI, 2.41-4.40). Same pattern was seen for very and moderately preterm births and SGA. Education was a strong predictor of both preterm birth and SGA but did not modify the association between maternal congenital heart disease and preterm birth (P=0.38) or SGA (P=0.99). Conclusions Women with CHD were at increased risk of preterm birth both, moderately and very preterm, as well as giving birth to infants SGA. Education was a strong predictor of both preterm birth and SGA but the association between CHD and risk of preterm birth and SGA was independent of educational level.