Selected midline defect associations: a population study.

Using data from the population-based Metropolitan Atlanta Congenital Defects Program, the association of seven relatively common and easily ascertainable groups of midline defects was studied. These defects were neural tube defects (575 patients), oral clefts (633 patients), omphalocele (141 patients), esophageal atresia/tracheoesophageal fistula (88 patients), imperforate anus (151 patients), conotruncal heart defects (289 patients), and diaphragmatic hernia (75 patients). Known syndromes were excluded from the analysis. Of 1743 infants with at least one midline defect, 86 (4.9%) had at least a second midline defect, and 9 (0.5%) had two additional midline defects. Pairwise analysis of the seven defects shows that, although most midline defects tend to be statistically associated with other midline defects, specific combinations of midline defects are seen. For example, neural tube defects are more strongly associated with cleft lip with or without cleft palate than with cleft palate alone; imperforate anus is more strongly associated with spina bifida than with anencephaly or encephalocele. Moreover, some combinations of defects are not observed (eg, neural tube defect and conotruncal heart defect, clefts and diaphragmatic hernia, omphalocele and esophageal atresia/tracheoesophageal fistula). These data point to the need for further refinement in the study of the association of midline defects in terms of embryologic and pathogenetic mechanisms because most midline defects tend to occur as an isolated defect, some midline defects occur with nonmidline defects (such as limb defects), and specific associations among midline defects are observed.