Statistical analyses
The data of the women with placental abruption were
reviewed. The maternal background
and obstetric outcomes were compared between women with and without
placental abruption. We also examined the frequency of placental
abruption according to the gestational age. The chi-square test and
Fisher’s exact test were used to compare the categorical variables, and
t-test was used to compare the continuous variables after confirming
that each of the continuous variables was normally distributed. The
adjusted OR (aOR) and 95% CI for placental abruption were calculated
using the multiple logistic regression model. The ORs were adjusted for
confounding variables, including history of placental abruption, ART
pregnancy, parity, maternal age, smoking during pregnancy, BMI before
pregnancy, chronic hypertension, and uterine myoma. In the logistic
regression model, dummy variables were used for the categorical
variables that consisted of more than three categories. All statistical
analyses were conducted using SPSS, version 26 (IBM Corp., Armonk, NY,
USA). The differences with P <0.05 were considered
statistically significant.