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.