Strengths and limitations
Our study has several strengths. First, all the patients were have their
prenatal examination and delivered at our institution, where the
clinical data were relatively complete. Second, our research had a large
sample and a long research time span, which would be more
representative. However, there are some limitations to this study. Due
to the impact of retrospective analysis, the three groups of people had
heterogeneity, and there is subjectivity in the selection of placental
pathology, which may lead to bias. In addition, this study lacks a
normal placental control group , and further prospective randomized
controlled trials are still needed in the future.