Study design and selection of participants
We retrospectively analyzed data of a cohort of pregnant women with a
short cervix. All women had their delivery at Peking University First
Hospital in Beijing, China, from January 1, 2017 to January 1, 2018. In
our center, the pregnancies underwent transvaginal ultrasonography
throughout the gestational period and the cervical length is routinely
measured. A short cervix was defined as cervical length < 25mm
under transvaginal ultrasonography. In women showing signs of
miscarriage such as bleeding and contraction, we also recommended
transvaginal ultrasonography. Patients with triple gestations, who
underwent induced abortions due to personal reasons and patients
whose
short cervix was first detected after 36 weeks were excluded from this
study. Women had received a preventive cervical ligation treatment were
also excluded from this study. In the analysis of PTB < 34
weeks, pregnancies whose short cervix was first detected after 33 weeks
were excluded.(Figure 1) The sonographers who performed the
scans were extensively trained and passed a practical examination
administered by an expert organization of Beijing.