2 MATERIALS AND METHODS
This was a retrospective study in the Fetal Medicine Center of the First Affiliated Hospital of Chongqing Medical University in Chongqing, China, between January 2017 and June 2020. As this was a retrospective analysis of routinely collected anonymized clinical data, the local Ethics Committee confirmed that no ethical approval from the patients was necessary in accordance with the national regulations.
SGA was defined as a customized birth weight between the 3rd and 10th centiles, and FGR was defined as a birth weight < 3rd centile15. Late-onset fetal growth restriction (FGR) is usually defined as that diagnosed >32 weeks of pregnancy. Adverse perinatal outcomes included emergency cesarean section for non-reassuring fetal status, 5-min Apgar score < 7 and neonatal acidosis at birth 16. According to the ACOG guideline 17, all of the SGA with normal umbilical artery Doppler included in our study were delivered at about 37 weeks of gestation. The gestational age (GA) was determined according to the last menstrual period, the first-trimester crown-rump length or the head circumference when the first ultrasound examination was performed after 14 weeks of gestation.
The inclusion criteria for three groups were as follows: (1) singleton gestation, (2) intact membranes, (3) absence of congenital or chromosomal abnormalities, (4) absence of pregnancy complications (i.e. hypertensive disorders, diabetes), (5) normal amniotic fluid, (6) the UA-PI within the normal range for GA, (7) SGA and FGR were delivered at 37 ± 2 weeks and (8) an ultrasound examination, including fetal biometry and UA velocities, was performed at 37 ± 2 weeks for all fetuses. The parameters of UA velocities included the umbilical artery end-diastolic velocity (UA-EDV), umbilical artery peak systolic velocity (UA-PSV), umbilical artery mean diastolic velocity (UA-MDV) and umbilical artery time-averaged maximum velocity (UA-TAMXV).
The normality of the data was determined by Kolmogorov-Smirnov test. Continuous variables were expressed as the means ± standard deviations or the Medians (interquartile ranges) as appropriate. Categorical variables were expressed as the numbers of cases. For multiple comparisons, one-way analysis of variance (ANOVA) was performed for continuous variables, and pearson’s chi-square test was performed for categorical variables. Logistic regression analysis was performed to identify the predictive factors of FGR. The predictive performance for FGR was determined by receiver–operating characteristics (ROC) curve analysis. P < 0.05 was considered to be statistically significant. All P values were two-sided, and P values of less than 0.05 were considered statistically significant. Statistical analyzes were performed using SPSS version 21.0 (IBM Corporation, Armonk, NY, USA) and MedCalc version 11.4.2 (MedCalc Software, Ostend, Belgium).