How to determine the causes and recurrence risks of congenital anomalies - a clinical approach

Major anomalies occur in 3-5% of newborns and usually require medical or surgical intervention.

Minor anomalies are variants of no serious medical or cosmetic significance and occur in less than 4% of the population. They occur in physical features of complex and variable development - anomalies of hair patterning, eye spacing, ear form, palmar creases and digits. As almost any minor variant may occasionally be found as a usual feature in a particular family, parents and other family members should be examined before assuming that the feature is part of a syndrome.

Three or more minor anomalies are found in only 0.5% of babies but 90% of these have one or more major defects as well. The finding of several minor anomalies in an individual is unusual and often indicates that a more serious problem in morphogenesis has occurred. Minor variants are extremely helpful in the diagnosis of syndromes postnatally.

Single malformations may occur as isolated anomalies, in an otherwise normal child.

Several anomalies together may suggest a specific diagnosis. Common recognisable patterns of major anomalies are most likely to be due to chromosomal imbalance, but certain combinations may also suggest rare single gene or dysmorphic syndromes or teratogens.