Multivariable logistic regression analysis of the associations between other pregnancy outcomes and IPIs (Tables 4, 5, 6, 7, 8, and 9)
Multivariable logistic regression analysis using an IPI of 24-59 months as the reference category was conducted to examine the associations between different IPIs and adverse perinatal outcomes among 1662 women with previous CS. Model 1 did not adjust for any confounding factors (Table 4), while model 2 adjusted for maternal age, maternal BMI, educational status, assisted reproductive technology (ART), number of previous CSs, previous vaginal delivery and previous emergency CSs (Table 5). In model 1, an IPI of less than 24 months significantly increased the risk of incomplete uterine rupture (OR 1.30, 95% CI 1.05-1.61), while an IPI of 60 to 119 months (OR 0.77, 95% CI 0.62-0.95) and 120 months or greater (OR 0.59, 95% CI 0.38-1.08) significantly reduced the risk of incomplete uterine rupture. In model 2, after adjustments for some confounders, the results suggested that the IPI was not a risk factor for incomplete uterine rupture. In models 1 and 2, we found that IPI had no effect on other adverse perinatal outcomes, including pernicious placenta, abnormal placental position, PROM, PPH, hysterectomy, low 1-min Apgar score, and admission to the NICU.
Studies have confirmed that emergency CS can significantly increase the risk of adverse perinatal outcomes.22 The other four models were established by using multivariable logistic regression analysis to analyze the relationship between the IPI of 552 women with emergency CS and that of 1099 women with elective CS and perinatal outcomes separately. Model 3 did not adjust for any confounding factors in women with emergency CS (Table 6), while model 4 adjusted for maternal age, maternal BMI, educational status, ART, number of previous CSs, and previous vaginal delivery (Table 7). In models 3 and 4, the association between IPI and incomplete uterine rupture among women with emergency CS always remained nonsignificant (p > 0.05). Model 5 did not adjust for any confounding factors among women with elective CS (Table 8), while model 6 adjusted for maternal age, maternal BMI, educational status, ART, number of previous cesarean sections, and previous vaginal delivery (Table 9). In model 5, IPI was a risk factor for incomplete uterine rupture (p = 0.048). An IPI of less than 24 months significantly increased the risk of incomplete uterine rupture (OR 1.35, 95% CI 1-1.82), and an IPI of 60 to 119 months (OR 0.74, 95% CI 0.55-1) or 120 months or greater (OR 0.55, 95% CI 0.3-0.99) significantly reduced the risk of incomplete uterine rupture. In model 6, after adjustments for some confounders, we found that the IPI of women with a history of selected CS was not a risk factor for incomplete uterine rupture (p = 0.131).