Fetal-to-placental weight ratio adjusted for key factors: a cohort study

Abstract

Objective: To assess the association between placental weight and birthweight, exploring fetal-to-placental ratio (FPR) adjusting for parity, sex and PAPP-A and β-hCG levels. Methods: A retrospective cohort study was conducted at a tertiary university hospital. We included singleton pregnancies undergoing first-trimester screening and delivering at the same hospital between May 2013 and September 2024. Clinical data were gathered from electronic databases (SClínico®, ObsCare®, ASTRAIA®). Continuous variables were assessed through ANOVA or T test. Pearson or Spearman correlation was applied as appropriate. Linear regression assessed independent variables' impact. For significance, a p-value<0.05 was assumed. All data was processed with IBM SPSS v29.0. Results: Among 16492 singleton pregnancies, 54.9% women were nulliparous and 8.9% newborns were small for gestational age. Placental weight was positively correlated with birthweight (r=0.517,p<0.001), which increased by 1.77g per gram of placental weight, explaining 26.7% of the birthweight variation. Preterm deliveries (6.8%) had lower mean placental weight (493.1g versus 579.2g) and birthweight (900g difference, p<0.001) compared to term group. Mean male fetuses' birthweight was 121.3g higher than female (p<0.001). Female fetuses and nulliparity were associated with decreased placental weight (p<0.001). On average, the FPR was 6:1, with male fetuses exhibiting greater FPR (p<0.001) as well as term deliveries (p<0.001). FPR was correlated with 5-minute Apgar score (Apgar<7:5.0 vs. Apgar≥7:5.7, p<0.001) and revealed a weak negative association with PAPP-A levels and β-hCG levels (p<0.001). However, parity (p=0.121) showed no significant association with FPR. Conclusion: Placental weight correlates with birthweight. FPR is influenced by sex and gestational age.