Routine assessment of cerebroplacental ratio at 35-37 weeks' gestation in the prediction of adverse perinatal outcome

Background: Third trimester studies in selected high-risk pregnancies have reported that low cerebroplacental ratio (CPR), due to high pulsatility index (PI) in the umbilical artery (UA), and or decreased PI in the fetal middle cerebral artery (MCA), is associated with increased risk of adverse perinatal outcomes. Objective: To investigate the predictive performance of screening for adverse perinatal outcome by the cerebroplacental ratio (CPR) measured routinely at 35+6 - 36+6 weeks’ gestation. Methods: This was a prospective observational study in 47,211 women with singleton pregnancies undergoing routine ultrasound examination at 35+6 - 36+6 weeks’ gestation, including measurement of UA-PI and MCA-PI. The measured UA-PI and MCA-PI and their ratio were converted to multiples of the median (MoM) after adjustment for gestational age. Multivariable logistic regression analysis was used to determine whether CPR improved the prediction of adverse perinatal outcome that was provided by maternal characteristics, medical history and obstetric factors. The following outcome measures were considered: first, adverse perinatal outcome consisting of stillbirth, neonatal death or hypoxic ischemic encephalopathy grades 2 and 3, second, presence of surrogate markers of perinatal hypoxia consisting of umbilical arterial or venous cord blood pH ≤7 and ≤7.1, respectively, 5-minute Apgar score 24 hours, third, cesarean section for presumed fetal distress in labor, and fourth, neonatal birthweight <3rd percentile for gestational age. Results: Low CPR was associated with increased risk of adverse perinatal outcome, presence of surrogate markers of perinatal hypoxia, cesarean section for presumed fetal distress in labor and birth of neonates with birthweight