Variables of interest
We scrutinized the sonographic reports in the electronic database of the
hospital to identify patients with a short cervix. The relevant
information was then collected from the electronic medical records using
their hospital identity of each patient. Throughout the study period, no
significant changes was made to the electronic medical database.
We collected the demographic characteristics, obstetric data, risk
history, and preexisting comorbidities. The demographic characteristics
included were: maternal age at conception and body mass index (BMI)
before pregnancy. For robust clinical assessment, BMI was classified
into “normal” (18.5≤ BMI ≤23.9kg/m2), “overweight”
(24≤ BMI ≤27.9kg/m2) and “obesity” (BMI
≥28kg/m2) groups12. None of the
women was a smoker or drinker, thus lifestyle factors (e.g., smoking and
drinking) were not analyzed in this study. In the obstetrics data,
gestational age at diagnosis of short cervix, cervical length and
amniotic fluid sludge were collected when the patient’s short cervix was
first detected. Risk history was defined as having a previous short
cervical length or PTB (e.g., induced abortion, intrauterine operation
frequency (except abortion) and history of preterm birth). Autoimmune
diseases included in the preexisting comorbidities was defined as
systemic lupus erythematosus (SLE) or antiphospholipid syndrome (APS)
that was found to be related to PTB13. To explore the
relationship between some pregnancy complications and PTB among
participants, we collected data such as polyhydramnios, gestational
diabetes mellitus, and blood pressure state.