Results
In total, 104,102 records were identified during the study period. Of those, 1,994 records from women with multiple gestation pregnancies and 7,698 records of women with missing data were excluded from the analysis (Figure 1). After applying our exclusion criteria, the data of 94,410 maternal participants were included in the analysis. Among 94,410 participants, 416 women had placental abruption and 93,994 women were without placental abruption. The prevalence rate of placental abruption was 0.4% (416/94410). Almost half (44.1%) of the placental abruption cases occurred prematurely before the gestational age of 37 weeks (Figure 2A).
Table 1 summarizes the maternal characteristics and obstetric outcomes of the participants stratified by the presence and absence of placental abruption.
The rate of CS in women with placental abruption was 62.2%, which was significantly higher than that in women without placental abruption (18.6%, P <0.001). Among women with placental abruption, the rate of CS dropped rapidly after 37 weeks of pregnancy (Figure 2B).
Table 2 shows the results of the logistic regression analyses. After adjusting for potential confounding factors, history of placental abruption (aOR: 3.5, 95% CI: 1.3–9.6, P =0.013), ART (aOR: 1.7, 95% CI: 1.1–2.7,P =0.021), maternal age <20 years (aOR: 2.8, 95% CI: 1.2–6.5, P =0.016), maternal age ≥35 years (aOR: 1.7, 95% CI: 1.1–2.5, P =0.024), smoking during pregnancy (aOR: 1.7, 95% CI: 1.2–2.5, P =0.003), and chronic hypertension before pregnancy (aOR: 4.0, 95% CI: 2.5–6.2, P <0.001) were associated with placental abruption. When no parity was set as a reference, no association was observed between the number of parities and risk of placental abruption.