Third-Trimester Cerebroplacental Ratio and Preceding Fetal Growth in Appropriate-for-Gestational-Age Fetuses: Limited Individual-Level Information in a Longitudinal Cohort

Background/Objectives: Cerebroplacental ratio (CPR) is mainly a contemporaneous hemodynamic and prognostic marker but has also been proposed as a marker of impaired growth velocity. We quantified how much third-trimester CPR constrains an individual fetus’s preceding measured growth. Methods: In a retrospective single-center cohort, conditional estimated fetal weight growth (cEFW) was derived in 920 singleton pregnancies and analyzed in 760 fetuses appropriate for gestational age (AGA) at the third-trimester scan (median 32.9 weeks), with umbilical and middle cerebral artery Doppler measurements obtained during the same examination. Quantile regression estimated the conditional/unconditional 10th–90th percentile width of cEFW (width ratio) by within-cohort CPR z-score. Results: Each 1 SD increase in CPR corresponded to 0.100 SD higher cEFW (95% CI 0.040–0.160); the AUC for cEFW ≤ −1 SD was 0.553 (0.479–0.619). Point-estimate width ratios ranged from 0.968 to 1.194 between CPR z −2 and +1, with wide intervals at low CPR. The modeled probability of cEFW ≤ −1 SD was 14.4% (8.5–22.1) at z −2 and 10.5% (8.4–12.9) at z 0. Without AGA restriction (n = 878), the association was stronger (AUC 0.615), but point-estimate width ratios likewise showed no narrowing at low CPR. Conclusions: In AGA fetuses scanned mainly at 31–34 weeks, CPR provided limited individual-level information about preceding measured growth in terms of central 80% width, discrimination and lower-tail probabilities; at very low CPR, meaningful narrowing cannot be excluded. Prognostic value for perinatal outcome was not assessed.