Causes of neonatal and postneonatal death among infants with birth defects in Texas

Enhancing the Classification of Congenital Heart Defects for Outcome Association Studies in Birth Defects Registries

INTRODUCTION

Traditional strategies for grouping congenital heart defects (CHDs) using birth defect registry data do not adequately address differences in expected clinical consequences between different combinations of CHDs. We report a lesion-specific classification system for birth defect registry-based outcome studies.

METHODS

For Core Cardiac Lesion Outcome Classifications (C-CLOC) groups, common CHDs expected to have reasonable clinical homogeneity were defined. Criteria based on combinations of Centers for Disease and Control-modified British Pediatric Association (BPA) codes were defined for each C-CLOC group. To demonstrate proof of concept and retention of reasonable case counts within C-CLOC groups, Texas Birth Defect Registry data (1999-2017 deliveries) were used to compare case counts and neonatal mortality between traditional vs. C-CLOC classification approaches.

RESULTS

C-CLOC defined 59 CHD groups among 62,262 infants with CHDs. Classifying cases into the single, mutually exclusive C-CLOC group reflecting the highest complexity CHD present reduced case counts among lower complexity lesions (e.g., 86.5% of cases with a common atrium BPA code were reclassified to a higher complexity group for a co-occurring CHD). As expected, C-CLOC groups had retained larger sample sizes (i.e., representing presumably better-powered analytic groups) compared to cases with only one CHD code and no occurring CHDs.

DISCUSSION

This new CHD classification system for investigators using birth defect registry data, C-CLOC, is expected to balance clinical outcome homogeneity in analytic groups while maintaining sufficiently large case counts within categories, thus improving power for CHD-specific outcome association comparisons. Future outcome studies utilizing C-CLOC-based classifications are planned.

Racial and ethnic differences in infant survival for hydrocephaly-Texas, 1999-2017

BACKGROUND

Congenital hydrocephaly, an abnormal accumulation of fluid within the ventricular spaces at birth, can cause disability or death if untreated. Limited information is available about survival of infants born with hydrocephaly in Texas. Therefore, the purpose of the study was to calculate survival estimates among infants born with hydrocephaly without spina bifida in Texas.

METHODS

A cohort of live-born infants delivered during 1999-2017 with congenital hydrocephaly without spina bifida was identified from the Texas Birth Defects Registry. Deaths within 1 year of delivery were identified using vital and medical records. One-year infant survival estimates were generated for multiple descriptive characteristics using the Kaplan-Meier method. Crude hazard ratios (HRs) for one-year survival among infants with congenital hydrocephaly by maternal and infant characteristics and adjusted HRs for maternal race and ethnicity were estimated using Cox proportional hazard models.

RESULTS

Among 5709 infants born with congenital hydrocephaly without spina bifida, 4681 (82%) survived the first year. The following characteristics were associated with infant survival: maternal race and ethnicity, clinical classification (e.g., chromosomal or syndromic), preterm birth, birth weight, birth year, and maternal education. In the multivariable Cox proportional hazards model, differences in survival were observed by maternal race and ethnicity after adjustment for other maternal and infant characteristics. Infants of non-Hispanic Black (HR: 1.28, 95% CI: 1.04-1.58) and Hispanic (HR: 1.31, 95% CI: 1.12-1.54) women had increased risk for mortality, compared with infants of non-Hispanic White women.

CONCLUSIONS

This study showed infant survival among a Texas cohort differed by maternal race and ethnicity, clinical classification, gestational age, birth weight, birth year, and maternal education in infants with congenital hydrocephaly without spina bifida. Findings confirm that mortality continues to be common among infants with hydrocephaly without spina bifida. Additional research is needed to identify other risk factors of mortality risk.

Contribution of Preterm Birth to Mortality Among Neonates with Birth Defects

OBJECTIVE

To estimate the proportion of neonatal mortality risk attributable to preterm delivery among neonates with birth defects.

STUDY DESIGN

Using a statewide cohort of live born infants from the Texas Birth Defects Registry (1999-2014 deliveries), we estimated the population attributable fraction and 95% CI of neonatal mortality (death <28 days) attributable to prematurity (birth at <37 weeks vs ≥37 weeks) for 31 specific birth defects. To better understand the overall population burden, analyses were repeated for all birth defects combined.

RESULTS

Our analyses included 169 148 neonates with birth defects, of which 40 872 (24.2%) were delivered preterm. The estimated proportion of neonatal mortality attributable to prematurity varied by birth defect, ranging from 12.5% (95% CI: 8.7-16.1) for hypoplastic left heart syndrome to 71.9% (95% CI: 41.1-86.6) for anotia or microtia. Overall, the proportion was 51.7% (95% CI: 49.4-54.0) for all birth defects combined.

CONCLUSIONS

A large proportion of deaths among neonates with birth defects are attributable to preterm delivery. Our results highlight differences in this burden across common birth defects. Our findings may be helpful for prioritizing future work focused on better understanding the etiology of prematurity among neonates with birth defects and the mechanisms by which prematurity contributes to neonatal mortality in this population.

Survival of infants and children born with severe microcephaly, Texas, 1999-2015

BACKGROUND

Severe microcephaly is a brain reduction defect where the delivery head circumference is <3rd percentile for gestational age and sex with subsequent lifelong morbidities. Our objective was to evaluate survival among 2,704 Texas infants with severe microcephaly delivered 1999-2015.

METHODS

Infants with severe microcephaly from the Texas Birth Defects Registry were linked to death certificates and the national death index. Survival estimates, hazard ratios (HR) and confidence intervals (CI) were calculated using the Kaplan-Meier method and Cox proportional hazards models stratified by presence versus absence of co-occurring defects.

RESULTS

We identified 496 deaths by age 4 years; most (42.9%) occurred in the neonatal period, and another 39.9% died by 1 year of age. Overall infant survival was 84.8%. Lowest infant survival subgroups included those with chromosomal/syndromic conditions (66.1%), very preterm deliveries (63.9%), or co-occurring critical congenital heart defects (44.0%). Among infants with severe microcephaly and a chromosomal/syndromic co-occurring defect, the risk of death was nearly three-fold higher among those with: proportionate microcephaly (i.e., small baby overall), relative to non-proportionate (HR = 2.84, 95% CI = 2.17-3.71); low-birthweight relative to normal (HR = 2.72, 95% CI = 1.92-3.85); critical congenital heart defects (CCHD) relative to no CCHD (HR = 2.90, 95% CI = 2.20-3.80). Trisomies were a leading underlying cause of death (27.5%).

CONCLUSIONS

Overall, infants with severe microcephaly had high 4-year survival rates which varied by the presence of co-occurring defects. Infants with co-occurring chromosomal/syndromic anomalies have a higher risk of death by age one than those without any co-occurring birth defects.