1028: Utility of the cerebroplacental ratio (CPR) in marijuana exposed growth restricted fetuses

Abstract

Severe fetal growth disorders are associated with an increased risk of adverse perinatal outcome (APO). The CPR represents the interaction of alterations in blood flow to the fetal brain and placenta. It is calculated by dividing the Doppler indices of the middle cerebral artery (MCA) by those of the umbilical artery (UA). CPR has been toted as a superior reflection of fetal hypoxia/acidemia and therefore a better predictor of APO. We sought to determine the role of CPR as a predictor of severe fetal growth restriction (FGR), defined as an estimated fetal weight (EFW) less than the 5th percentile, in a study population of marijuana (MJ) exposed FGR fetuses. This was a retrospective cohort study of high-risk singleton pregnancies over a four-year period. Self-identified daily MJ users with FGR fetuses, defined as fetuses with an EFW less than the 10th percentile, in the 3rd trimester were isolated. Fetal biometry, amniotic fluid indices, and CPRs were calculated. A CPR < 1 was considered abnormal. FGR fetuses with normal and abnormal CPRs were then compared. 26 /192 (13.5%) of MJ exposed fetuses were diagnosed with FGR in 3rd trimester. 12/26 (46%) had an abnormal CPR and 14 had a normal CPR (mean CPR 0.60 vs 1.57, p = 0.0001). The mean EFW percentile was lower in the abnormal CPR group in comparison to the group with normal CPR (3.33 vs 7.64, p=0.0001). Both groups showed evidence of brain sparing with an overall mean head circumference of 17.55 in comparison to a mean abdominal circumference of 5.63. A CPR < 1 was associated with more severe FGR, oligohydramnios, and abnormal UA Doppler studies (see table 1). Approximately half of the MJ exposed FGR fetuses had an abnormal CPR. In this subset of patients, > 90% had severe FGR, a higher proportion had absence/reversal of end diastolic flow in the UA, and a higher proportion had oligohydramnios. This demonstrates that an abnormal CPR identifies a group of FGR fetuses at a greater risk for severe FGR and possibly APO.