2.2| Data collection
Data were extracted from the medical
charts. Demographic characteristics included maternal age, prepregnancy
body mass index (prepregnancy BMI), nulliparity, history of previous
cervical surgery, history of smoking, clinical data including validation
of gestational age by first trimester ultrasound, chorionicity, history
of previous preterm or late abortion, complications during pregnancy,
use of assisted reproductive technology, cervical length (20-24 weeks)
and cervical funneling, gestational age at delivery.
Gestational age was calculated from the last menstrual period (LMP) and
confirmed by the foetal crown-rump length measurement at the first
trimester ultrasonic scan. If a discrepancy of more than 7 days was
observed, the sonographic gestational age was followed. Chorionicity was
confirmed by identifying lambda and T signs with ultrasound imaging
between 11+0 and 13+6 weeks of
gestation.21
All patients underwent transvaginal cervical length (TVCL) measurements
between 20-24 weeks prior to viability and at a gestational age when the
optimal image of the cervix was relatively easy to capture. The TVCL
measurements of all subjects were performed by experienced sonographers
at our ultrasound units. The ultrasound assessment was performed to
measure the length of the cervical canal from the internal os to the
external os and observe whether the cervical funneling appears with
patients in the lithotomy position with an empty bladder. The
measurement was repeated under fundal pressure or the Valsalva manoeuvre
unless severe cervical shortening was observed.16 In
addition, all the ultrasonic reports were reviewed in detail for
information on the presence, shape and length of cervical funneling; the
length of the closed part of the cervix; and changes in cervical
funneling and the closed part in response to increased abdominal
pressure.23