Study limitations
This was a retrospective single-center study in which data were collected from medical records. We focused on the delivery period, as most patients were referred in the later stages of pregnancy, and we were often unable to obtain information on events occurring early during pregnancy, the subsequent analysis may be biased in that sense. Meanwhile, a few data remained incomplete, incorrectly entered, or unavailable. In addition, there was a lack of data on scheduled or unscheduled cesarean sections. Moreover, some simple CHD such as PFO, ASD with small defect, actually have very little impact on the body, which can cause bias. What’s more, there were also differences in the number, age, and other aspects of specific CHD between the two groups, which can also cause selection bias.