Cleft lip is most closely associated with advanced maternal age, as older maternal age has been linked to an increased risk of craniofacial malformations including orofacial clefts. The risk is thought to be related to age-related changes in oocyte quality and genetic factors influencing embryonic development. Proper understanding of this association is crucial for prenatal counseling and risk assessment. Early diagnosis allows for timely surgical repair, which typically involves cleft lip closure around 3 months of age to optimize functional and aesthetic outcomes.

Reference: Nelson Textbook of Pediatrics, Kliegman RM, 21st Edition.