Background: In general, the existing evidence points to a role for maternal sleep in pregnancy complications and fetal growth, however, little has been focused on birth defects. We aimed to explore the association between periconceptional poor sleep and the risk of congenital heart disease (CHD), and to examine if daytime napping could to some extent change the association. Methods: A case-control study was conducted in Shanghai Children's Medical Center, in which, a total of 524 cases (262 simple CHD vs. 262 severe CHD), along with 262 controls. Results: In the multivariable logistic analysis, poor sleep could increase the risk of both simple CHD (OR = 2.486, 95% CI = 1.619-3.818) and severe CHD (OR = 1.950, 95% CI = 1.269-2.997), while routine daytime nap could decrease risk of simple CHD (OR = 0.634, 95% CI = 0.435-0.923). In the stratified analysis, the concurrence with routine daytime nap could weaken the risk of simple CHD caused by poor sleep (OR = 3.183, 95% CI: 1.830-5.537 decreased to OR = 2.236, 95% CI: 1.200-4.165). The examinations were repeated in ventricular septal defect and tetralogy of Fallot, and the established associations can be verified. Moreover, all these findings were also similarly observed in both propensityscore-adjusted and propensity-score-matched analyses. Conclusions: Poor maternal sleep around periconceptional period seems to be an independent risk factor for CHD. The concurrence with daytime nap could to some extent reduce the risk in simple CHD. The results individually and collectively put forward the importance of maternal sleep in embryonic heart development. K E Y W O R D S case-control study, congenital heart disease, daytime nap, maternal sleep, pregnancy Anda Zhao and Kena Zhao contributed equally to this work.