Methods
This is a prospective cohort study in pregnant women with a term
singleton pregnancy in latent phase of labour or prior to labour
induction at the Prince of Wales Hospital, Hong Kong SAR. This series is
an expansion from the initial study of 218 cases who delivered at our
hospital between May 2019 and December 2019 16. The
gestational age was calculated using the first date of the last
menstrual period and confirmed by the measurement of foetal crown-rump
length in the first trimester or head circumference in the second
trimester 31. The entry criteria were a live fetus in
cephalic presentation between 37 complete weeks and 41 weeks 6 days of
gestation, either in the latent phase of labour or due to undergo
induction of labour. Women who were unconscious or severely ill, women
with learning disabilities or serious mental illnesses, women in labour
with cervical dilatation of 3 cm or more or when the estimated foetal
weight (EFW) was greater than 4.2 Kg where elective Caesarean delivery
is offered in our institute were excluded. The women who agreed to
participate in the study provided written informed consent, which was
approved by the Institutional Review Board (Joint Chinese University of
Hong Kong – New Territories East Cluster Clinical Research Ethics
Committee, Reference Numbers CRE-2017.608).
The ultrasonographic assessment of foetal growth, amniotic fluid volume,
placental location and Doppler velocimetry was performed
transabdominally using convex 2D 1-5 MHz probe of Voluson E6 (GE
Healthcare, Austria) or convex 2D 2-6 MHz probe Affiniti 50W (Philips
Healthcare, Amsterdam, Netherlands) by one of the five obstetricians
with at least three years of expertise in obstetric ultrasound (MSNL,
SM, AHWK, STKW, AWTT). The Hadlock model 3 was used to estimate foetal
size based on measurements of head circumference, abdominal
circumference, and femur length 32. The UA-PI was
measured from a free-floating section of the umbilical cord, while the
MCA-PI was measured from the proximal third of the vessel, taking care
not to compress the foetal head with the transducer. The UtA-PI was
measured within 1 cm of the crossing of the uterine artery with the
external iliac artery adopting a similar technique as previously
described for measuring the UtA-PI by the transabdominal approach during
the second trimester of pregnancy 33, 34. The
pulsatility indices from the right and left uterine arteries were
measured and the mean UtA-PI was calculated. During foetal quiescence,
all foetal parameters including biometry and Doppler indices were
measured in triplicate, with averages recorded. The CPR was calculated
as the ratio of MCA-PI to the UA-PI.
After the ultrasound evaluation, the participants had cCTG monitoring
for at least 60 minutes using the Sonicaid Team 3 Foetal Monitor, which
includes Dawes-Redman CTG analysis, together with the Sonicaid Centrale
Huntleigh software (Huntleigh Healthcare Ltd, Wales, United Kingdom).
The Dawes-Redman CTG analysis is a software that interprets the CTG
trace numerically based on the Dawes-Redman criteria. If all the
criteria are met, the software will perform the first analysis after 10
minutes of CTG tracing. If all the criteria are not met, the recording
and analysis continue to evaluate every 2 minutes until all criteria are
met, or until a maximum of 60 minutes. “Dawes-Redman criteria not met”
will be used to describe the CTG tracing only after 60 minutes of
monitoring. The participants were instructed to use an event marker
button to record foetal movements. If there were unsatisfactory CTG
findings based on conventional visual assessment during the tracing,
on-call obstetricians were notified, and the participant was managed in
accordance with our internally published and agreed-upon departmental
protocol. Participants with CTG tracing duration of less than 60 minutes
were not included in the statistical analysis.
During labour, the attending midwives and obstetricians were blinded to
the ultrasonographic Doppler and cCTG findings, except when
absent/reversed end diastolic flow in the UA was detected. The research
team as well as midwives and obstetricians were also blinded to the cCTG
findings to reduce bias. Induction of labour and intrapartum care were
both carried out in accordance with hospital departmental protocol and
practice. An experienced obstetrician determined the Bishop score. If
the cervix was favourable (Bishop score ≥6), labour was induced with
amniotomy followed by oxytocin. If the cervix was unfavourable (Bishop
score <6), 10 mg Dinoprostone slow-release vaginal pessary
(Propess, Ferring Pharmaceuticals, Saint-Prex, Switzerland) was used to
induce labour. Women with an unfavourable cervix were reassessed 24
hours later; if the cervix remained unfavourable, another Propess was
administered, and if the cervix was favourable, an amniotomy was
performed. If the woman remained in the latent phase after 12 hours of
oxytocin infusion, or if the cervix failed to dilate at a rate ≥1
cm/hour for ≥2 hours when the cervix was >4 cm dilated, a
Caesarean delivery was indicated due to lack of labour progress. The
attending obstetricians will interpret the CTG during active labour, and
further management, including instrumental or Caesarean delivery, would
be carried out in accordance with the department protocol based on their
clinical assessment and evaluation. The presence of recurrent variable
or late decelerations and/or reduced variability was used to identify
pathological CTG 3, 35.
Data on maternal and pregnancy characteristics, including age, weight,
height, racial origin, smoking, parity and gestational age, indications
for induction, pregnancy, and labour outcomes, such as mode of delivery,
birth weight, umbilical cord arterial pH and base excess, Apgar scores
at 1 and 5 minutes, and NICU/SCBU admission, were obtained from
computerised medical records and entered the secure research database.