870 Normalization of an abnormal second trimester cerebroplacental ratio in the third trimester equalizes perinatal risks

Abstract

An abnormal cerebroplacental ratio (CPR) is associated with increased risk of adverse perinatal outcomes. It is unknown if these risks persist with normalization of the cerebroplacental ratio later in gestation. This is a sub-analysis of a retrospective cohort study that utilized data from all non-anomalous singleton pregnancies that underwent Doppler assessment of the CPR between 20-28 weeks gestation at a single tertiary referral center. The perinatal outcomes of patients who had reassessment of the CPR after 32 weeks gestation were analyzed. The final CPR obtained before delivery was used. An abnormal ratio was defined as less than 5th percentile for gestational age. Adverse perinatal outcomes included preterm delivery, a small for gestational age neonate, and neonatal intensive care unit admission. 2326 patients were included in the original study, of which 3.9% had an abnormal CPR in the second trimester. 32 (35.1%) of these patients did not have reassessment of the CPR after 32 weeks, either due to delivery before 32 weeks (37.5%) or because the ratio was not obtained (62.5%). Patients with an abnormal CPR in the second trimester that had no ultrasound reassessment in the third trimester had a significantly earlier gestational age at delivery (34.8 weeks) compared to patients with a normal CPR that had no ultrasound reassessment (38.5 weeks). Of patients with an abnormal CPR in the second trimester, 50 (54.9%) experienced normalization of the cerebroplacental ratio after 32 weeks gestation. These patients were not significantly more likely to experience preterm delivery, a small for gestational age neonate, or neonatal intensive care unit admission when compared to patients who maintained a normal ratio throughout gestation. The association of adverse perinatal outcome with an abnormal second trimester cerebroplacental ratio is driven mostly by very preterm birth (<32 weeks). In approximately half of patients, the ratio normalized in the third trimester and was then associated with an average risk for an adverse outcome.