Modeling third trimester gestational age using transcerebellar diameter and fetal kidney length: A comparative statistical evaluation

Accurate estimation of gestational age (GA) in the third trimester remains a clinical challenge, particularly in low-resource settings where early ultrasound dating or reliable menstrual history may be unavailable. This study evaluates the predictive validity of the transcerebellar diameter (TCD) and the length of the fetal kidney (FKL) to estimate the third-trimester GA within a Nigerian cohort, to improve diagnostic precision using alternative biometric parameters. Data from 239 singleton pregnancies were collected prospectively from two tertiary hospitals in Lagos, Nigeria. Pearson’s correlation, linear regression, polynomial regression of degree 2 and generalized additive models (GAM) were employed to examine the relationship between TCD, FKL and clinically assigned GA. Six models were developed, individual and combined, for TCD and FKL, and their performance was compared. The agreement between predicted and clinical GA was assessed using the Welch t-test. Both TCD and FKL showed strong correlations with GA ($r=0.7315$ and $r=0.7317$; $p<0.001$), with GAM outperforming other models in predictive precision. No significant differences were observed between the clinical and predicted GA for all models ($p>0.05$). These findings suggest that both TCD and FKL are reliable in estimating GA in the third trimester, and GAM offers greater flexibility. The study supports the integration of these parameters into clinical protocols, especially for pregnancies with missed early ultrasounds or uncertain dates, and highlights their relevance in improving maternal-fetal care in sub-Saharan Africa.