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.