Patients
This was an observational, prospective study conducted in a single-center hospital with the approval of the Medical Institutional Ethics Committee. Eligible singleton pregnancies admitted at the Department of Obstetrics, Xiangyang NO.1 People's Hospital, Hubei University of Medicine, over a 2-year period from January 2017 to January 2019 were recruited. The inclusion criteria were described as follows: (a) aged between 18-45 years; (b) gestation age between 37-41 weeks; (c) underwent Doppler ultrasound before attending the labor room; (d) with completed clinical data from medical records. The exclusion criteria were described as follows: (a) maternal with antepartum hemorrhage, intrauterine infection, premature rupture of fetal membranes over 18 h, scarred uterus, or multiple gestations; (b) cervical dilatation ≥ 5 cm on admission; (c) fetuses with congenital malformations, e.g. structural or chromosomal anomalies; (d) planned cesarean delivery; (e) body mass index (BMI) > 40 kg/m2. Each enrolled participant offered signed informed consent.
Data collection
Maternal characteristics including age, BMI, smoking habits, conception (spontaneous or assisted), obstetric history, previous miscarriage, comorbidities of gestational diabetes, hypertension, and pre-eclampsia, gestational age at delivery, and route of delivery were extracted from the medical records. A same experienced operator was requested to perform the B-mode ultrasonography and Doppler ultrasound examination according to standard methodology (11). The ultrasound and Doppler parameters including MCA PI, UA PI, uterine artery PI, CPR, and oligohydramnios (defined as amniotic fluid index <5cm) were examined. CPR was calculated by dividing the MCA PI with UA-PI. MCA PI-to- uterine artery PI ratio was also calculated. Moreover, neonatal variables including birth weight, length at birth, head circumference, male gender, arterial pH, arterial base excess, glucose levels and lactate concentration were also detected and documented.
Outcome evaluation
An adverse perinatal outcome was set as the primary observational endpoint. According to the definitions by previous studies (12, 13), the adverse perinatal outcome includes stillbirth, early neonatal death, neonatal intensive care unit (NICU) admission ≥ 24h, Apgar score < 7 at 5 min, cesarean section for non-reassuring fetal status, meconium stained amniotic fluid, respiratory distress requiring oxygen support and mechanical ventilation, necrotizing enterocolitis, sepsis, hypothermia, and hypoglycemia.
Statistical analysis
Statistical analyses were performed using GraphPad prism 8.0 (GraphPad Inc., San Diego, CA, USA) and SPSS 19.0 (SPSS Inc., Chicago, IL, USA). Data analyses were carried out using the Chi-square test, Fisher’s exact test, Student t test, and Mann–Whitney U test as appropriate. The receiver operating characteristic (ROC) curve was plotted to investigate the predictive and cut-off values of MCA PI, CPR, and MCA/uterine artery PI ratio for adverse perinatal outcome using the Youden index. Independent risk factors for adverse perinatal outcome were assessed by the univariate and multivariate logistic regression analyses. A P value of < 0.05 was considered as statistically different.