Epidemiological analysis of the association between two congenital anomalies in the same child: a method for adjusting nonspecific clustering.

Most of the methods proposed to analyze patterns of congenital anomaly clusters have been criticized because large observed/expected (O/E) ratios are obtained for many defect combinations, suggesting that the association of congenital defects is a generalized and nonspecific tendency. To avoid this problem, two methods have been proposed: (1) the analysis of the association of two defects in the subgroup of infants with only multiple congenital anomaly (MCA) patterns, and (2) a method for adjusting the O/E ratio for the nonspecific tendency of defects to cluster among themselves. However, neither of these methods analyzes the association of only two particular defects in a child who apparently has no other anomalies apart from the two that are being analyzed. Here we present a method that analyzes the association of two particular defects, when they are the only defects observed in the child. The method is tested on the Spanish Collaborative Study of Congenital Malformations (ECEMC) data base. The proposed method also controls for the tendency of nonspecific defect clustering.