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

Objective: Fetal growth restriction (FGR) is associated with an increased risk of adverse perinatal outcomes. The cerebroplacental ratio (CPR) represents the interaction of alterations in blood flow to the fetal brain and placenta. CPR has been utilized as a superior reflection of fetal hypoxia/acidemia and therefore a better predictor of fetal morbidity. We sought to determine the role of the CPR as an adjunctive tool to identify fetuses at increased risk of adverse perinatal outcomes in a study population of marijuana (MJ) exposed FGR fetuses. Methods: This was a retrospective cohort study of high-risk singleton pregnancies over a 4-year period. Self-identified daily MJ users with FGR fetuses 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. Results: 26/192 (13.5%) of MJ exposed fetuses were diagnosed with FGR in the 3rd trimester. 12/26 (46%) had an abnormal CPR and 14 had a normal CPR (mean CPR 0.60 vs 1.57, p =.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 =.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. Conclusions: 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 of adverse perinatal outcomes.