CYP3A7 is a fetal-specific cytochrome P450 enzyme that represents 30-50% of total cytochrome P450 in fetal liver and 87-100% of total fetal hepatic CYP3A content 1. Originally thought exclusive to fetal tissues, CYP3A7 has been identified in neonates and developing infants up to 24 months post-gestational age 2. The enzyme exhibits developmental regulation, with expression peaking before birth and declining after birth 1, though significant interindividual variability (326-fold) exists among individuals 3. CYP3A7 metabolizes endogenous compounds critical for fetal development, including dehydroepiandrosterone sulfate (DHEA-S) and all-trans retinoic acid (atRA), as well as various xenobiotics 2. Expression is primarily regulated by glucocorticoids via glucocorticoid receptor signaling and by nuclear receptors (PXR, CAR, VDR, PPARα) 13. Transcriptional regulation involves Sp1, Sp3, and other transcription factors binding NF-κB-like elements in the promoter 4. Clinically, CYP3A7 expression shows ethnic variation in polymorphism frequencies 56, with implications for drug metabolism in fetuses, neonates, and select adult populations including pregnant women and cancer patients 2. Understanding CYP3A7 metabolism is essential for individualized pharmacotherapy in perinatal populations 2. The enzyme demonstrates ligand promiscuity similar to CYP3A4, metabolizing numerous substrates and inhibitors 7.