How do minor anomalies differ from major congenital malformations?

Minor anomalies and major congenital malformations differ primarily in their timing of development and their clinical nature.

Developmental Timing

• Major Congenital Malformations: These arise during the early stages of development, specifically during blastogenesis and organogenesis. They are often the result of interruptions in these critical early growth phases, which can be caused by mutant genes, chromosomal abnormalities, or environmental factors such as maternal infection or exposure to injurious substances.12
• Minor Anomalies: These are defined as arising during phenogenesis, the period of "attainment of final form" that occurs between days 57 and 266 of development.1

Characteristics

• Major Malformations: These involve significant structural defects, such as the absence of limbs, anencephaly, or cleft palate, which often have profound effects on function and health.3
• Minor Anomalies: These are subtle defects of appearance and structure that are evaluated subjectively or through measurement. While some may be internal and only discovered during an autopsy, they are generally considered the mildest of malformations and are relatively common in the population.1