Congenital Malformations Registry - Summary Report
Section V: Comparison of Selected Malformation Prevalence With Other Birth Defects Registries
Introduction to Table
The CMR relies on reports from hospitals and physicians for case ascertainment. Underreporting is an obvious concern, and the CMR over the years has developed methods to monitor hospital reporting. In this section, CMR live birth prevalences are compared with the national prevalence estimates for 21 selected defects developed by the Centers for Disease Control and Prevention (CDC) and the National Birth Defects Prevention Network (NBDPN).1 The 21 defects were selected because they are generally diagnosed soon after birth and the accuracy of diagnosis should be similar across sites1. These estimates were based on 11 registries which use active case-finding. Active case-finding uses data collection specialists who go to hospitals to identify and abstract records of children with malformations. The active case-finding systems were chosen because they have similar methodology and prevalence. Estimates are usually higher in systems using active case finding, although variations were observed even among the 11 active case finding systems (See Figure 1 in Canfield1).
As can be seen from Table 1, the CMR prevalences are equal to or higher than the lower boundary of the actual range of the 11 registries for 13 of the 21 defects (bold prevalences) and six of the defects are equal to or higher than the lower 95% Confidence Interval(CI) (boxed prevalences). The prevalences are generally higher for New York State not including New York City than for New York City (16 defect prevalences are equal to or higher than the lower boundary of the actual range of the 11 registries compared to 12 for New York City).
The interpretation of differences among registry prevalences is difficult. The lower prevalences of the CMR for Neural Tube Defects (NTD) is most likely due to the lack of reports on terminations as termination rates for NTDs are high (See CMR report 1998-2001, Section 6, NTD Surveillance and Trends). Lower prevalences for Anophthalmia/Microphthalmia might occur as some of these children have multiple defects and other defects may be reported but not the Anophthalmia/Microphthalmia. (Preliminary data from 2005 shows an increase in Anophthalmia/Microphthalmia which could be the result of the on-site audits. The lower prevalence for cleft lip with/without cleft palate is difficult to explain. There has been little variation in the prevalence since 1983 and it is an easily identified condition. There is also a wide variation within New York State itself from 5.3 in New York City to 13.0 in another region.
None of the 11 registries had all 21 defect prevalences fall within the 95% confidence intervals. Several registries would have the highest prevalence for one defect and the lowest prevalence for others. Variation among the registries in the rates of specific defects could reflect demographic differences in the populations as there are racial and ethnic differences in the rates of specific birth defects1. The prevalence of Down syndrome, Trisomy 18 and Trisomy 13 is highly dependent upon the maternal age distribution, age-specific pregnancy rates and women's use of prenatal diagnosis and pregnancy termination. The lower live birth prevalence rates of these chromosomal abnormalities in the CMR may be partially attributable to one or more of these factors. However, the source(s) of much of the variation is unclear and there may be true geographic differences. A comparison of birth defect prevalences between the Metropolitan Atlanta Congenital Defects Program (MACDP) and the California Birth Defects Monitoring Program (CBDMP) for the years 1983-1988 that adjusted for race, sex and maternal age showed regional differences in arm, hand and limb reduction defects2.
CMR staff will continue their efforts to improve reporting (See Section 6) and will continue to track our progress using the NBDPN national prevalence estimates.
a - Prevalence (number of defects per 10,000 live birth)