SPTB and preterm premature rupture of the membranes: Subclassification of sPTB into sPTB-noPPROM and PTB-PPROM demonstrated a downward trend in sPTB-noPPROM while PTB-PPROM increased significantly (singleton: sPTB-noPPROM average annual percent change (AAPC) -0.96, 95% CI -1.67 to -0.41; PTB-PPROM AAPC 3.4, 95% CI 2.89 to 4.18; iPTB AAPC 2.01, 95% CI 1.57 to 2.45; twin: sPTB-noPPROM AAPC -2.62, 95% CI -4.09 to -1.58; PTB-PPROM AAPC 3.05, 95% CI 2.46 to 3.72; iPTB AAPC 2.75, 95% CI 1.82 to 3.69).