Co-occurrence of birth defects and intellectual disability

This study used population-based databases to ascertain birth defects and intellectual disability (ID), defined as full IQ < 70, in children born in Western Australia during 1980-99. Of the children surviving to 1 year (n = 474 285), 4.9% had birth defects and 1.3% ID. ID was identified in 7.9% of children with birth defects. After adjusting for sex, mother's age, race, parity, plurality, birthweight and gestational age the prevalence ratio (PR) [95% confidence interval (Cl)] for ID in children with birth defects compared with those with no birth defects was 7.6 [7.2, 8.0]. Those with chromosomal anomalies comprised 3.2% of the group with birth defects. The percentage ID (and PR [95% CI]) in specific categories were: Down's syndrome 97% (84.5 [79.4, 90.0]), sex chromosome anomalies 30.3% (31.0 [23.8, 40.3]), other chromosomal anomalies 64.2% (54.2 [47.2, 62.3]). Birth defects were categorised according to system in the 96.8% of children with non-chromosomal anomalies. The percentage with ID (and PR [95% Cl]) for birth defects in each system were: spina bifida 18.8 (16.7 [12.2, 23.0]); nervous (except spina bifida) 38.6 (33.4 [30.3, 36.9]); cardiovascular 4.2 (4.1 [3.5, 4.8]); gastrointestinal 2.2 (2.0 [1.5, 2.7]); urogenital 2.6 (2.4 [2.0, 2.8]; musculo-skeletal 3.6 (4.0 [3.5, 4.6]); other non-chromosomal 7.0 (7.3 [6.5, 8.3]); and multiple systems 12.3 (10.2 [8.6, 12.2]).Birth defects were present in 30.2% of children with ID (27.7% of children with mild/moderate ID (IQ 40-69) and 54% of children with severe ID (IQ < 40)). Adjusted PRs for birth defects in children with any ID, mild/moderate ID and severe ID compared with children with normal intellectual function were 6.0 [5.8, 6.3], 5.5 [5.3, 5.8] and 10.5 [9.7, 11.4] respectively The data are useful for those providing services for children with developmental disabilities especially for predicting family support and respite and accommodation requirements for children and adults with severe ID.