Gestational Age Clocks
The cell type specificity of DNAm has complicated the use of the epigenetic clock to study pre-natal environmental exposures74 as the composition of cord blood is distinct from venous blood, thereby rendering clocks developed using venous blood unsuitable for gestational epigenetic age (GEA) predictions. The Horvath pan-tissue clock incorporated cord blood samples in its training set but set their CA at “0”75. This may lead to lower accuracy in neonatal blood samples as it does not account for their actual gestational age. Since then, gestational epigenetic clocks have been developed as summarized in Table 2 .
The study of the relationship between maternal exposures and DNAm has expanded rapidly. However, some studies use gestational age (as estimated through either last menstrual period or ultrasound methods)24 while others use GEA. Much like the use of EAA in childhood and adult studies, GEA can provide insight into the role of DNA methylation in traits in infancy.