(782) Transcerebellar diameter in fetal growth restriction - does concordance with estimated fetal weight matter?

Fetal growth restriction (FGR) is a significant risk factor for perinatal morbidity and mortality. Differentiating pathologic FGR due to placental insufficiency from a benign constitutionally small fetus remains challenging. We evaluated whether discordance between transcerebellar diameter (TCD) and estimated fetal weight (EFW) was associated with signs of pathologic FGR.

Study Design: We conducted a multi-center prospective study of singleton pregnancies with FGR (EFW < 10th%) diagnosed between 16 and 37.6 weeks gestation. We excluded those without confirmed first trimester dating, or with identifiable anatomic, genetic, or infectious etiologies of FGR. Cerebellum measurement was planned at each growth scan. Concordance between measures was defined as TCD < 25th% and EFW < 10th% and discordance TCD ≥ 25th% and EFW < 10th%. The primary outcome was a composite of signs of placental insufficiency (abnormal umbilical artery Dopplers, oligohydramnios, and/or abnormal antepartum testing). Secondary outcomes included gestational age (GA) at delivery, FGR resolution prior to delivery, neonatal outcomes, and hypertensive disorders of pregnancy (HDP). Associations between discordance and outcomes was estimated by the adjusted relative risk (95% confidence interval) through modified Poisson regression.

Results: Of the 128 participants enrolled, 68 had complete data on cerebellar measurements. Pregnancies with discordant measures were more likely to have signs of placental insufficiency compared to those with concordant measures (41.8% vs. 23.1%; aRR 1.63 (95% CI [0.57, 4.69])). Concordant pregnancies were diagnosed with FGR earlier and were more likely to resolve prior to delivery. Groups did not differ in GA at delivery, birthweight, rates of medically-indicated preterm birth, rates of SGA, other neonatal outcomes, and HDP.

Conclusion: FGR pregnancies with discordant TCD and EFW may be associated with signs of placental insufficiency, but due to high variability in the association, further confirmation of these findings is warranted. TCD discordance may be a tool for differentiating pathologic from benign FGR.