Total (n = 1,376)
Period 1 January 2010 to July 2015 (n = 704) Period 2 August 2015 to July 2020 (n = 756)
P-value
Maternal age (yr) 32 (30–35) 33 (31–36) <0.001*
Primiparity (%) 41.5 (292/704) 51.2 (387/756) <0.001**
Body mass index (kg/m2) before pregnancy 20.7 (19.3–22.8) 21.3 (19.5–24.2) <0.001*
History of preterm delivery (%) 11.5 (81/704) 9.39 (71/756) 0.186**
Multifetal pregnancy
Twin (%) 18.6 (131/704) 18.7 (141/756) 0.983**
Triplet (%) 1.4 (10/704) 2.1 (16/756) 0.315**
Pregnancy by in vitro fertilization-embryo transfer (%) 15.8 (111/704) 20.2 (153/756) 0.027**
Pregnancy by intrauterine insemination (%) 2.3 (16/704) 2.3 (17/756) 0.972**
Gestational age at admission (wk) 28.2 (24.6–32.4) 29.3 (24.1–33.1) 0.097*
Diagnosis at admission
Preterm premature rupture of membrane (%)
39.6 (279/704)
40.0 (302/756)
0.902**
Incompetent internal os of the cervix (%)
16.6 (117/704)
18.7 (141/756)
0.309**
Cerclage (%) 9.0 (63/704) 11.2 (85/756) 0.147**
Preterm labor (%) 41.3 (291/704) 35.7 (270/756) 0.027**
Short cervical length (%) 2.6 (18/704) 8.5 (64/756) <0.001**
Prior antibiotic treatment (%) 13.9 (98/704) 18.5 (140/756) 0.018**