Evaluating the proportion of isolated cases among a spectrum of birth defects in a population-based registry

Classification of isolated versus multiple birth defects: An automated process for population-based registries

Epidemiologic studies of birth defects often conduct separate analyses for cases that have isolated defects (e.g., spina bifida only) and cases that have multiple defects (e.g., spina bifida and a congenital heart defect). However, in some instances, cases with additional defects (e.g., spina bifida and clubfoot) may be more appropriately considered as isolated because the co-occurring defect (clubfoot) is believed to be developmentally related to the defect of interest. Determining which combinations should be considered isolated can be challenging and potentially resource intensive for registries. Thus, we developed automated classification procedures for differentiating between isolated versus multiple defects, while accounting for developmentally related defects, and applied the approach to data from the Texas Birth Defects Registry (1999-2018 deliveries). Among 235,544 nonsyndromic cases in Texas, 89% of cases were classified as having isolated defects, with proportions ranging from 25% to 92% across 43 specific defects analyzed. A large proportion of isolated cases with spina bifida (44%), lower limb reduction defects (44%), and holoprosencephaly (32%) had developmentally related defects. Overall, our findings strongly support the need to account for isolated versus multiple defects in risk factor association analyses and to account for developmentally related defects when doing so, which has implications for interpreting prior studies.

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.

Survival of neonates, infants, and children with birth defects: a population-based study in Texas, 1999-2018

Background

Birth defects are a leading cause of neonatal, infant, and childhood mortality, but recent population-based survival estimates for a spectrum in the U.S. are lacking.

Methods

Using the statewide Texas Birth Defects Registry (1999-2017 births) and vital records linkage to ascertain deaths, we conducted Kaplan-Meier analyses to estimate survival probabilities at 1, 7, and 28 days, and 1, 5, and 10 years. We evaluated survival in the full cohort of infants with any major defect and for 30 specific conditions. One-year survival analyses were stratified by gestational age, birth year, and case classification.

Findings

Among 246,394 live-born infants with any major defect, the estimated survival probabilities were 98.9% at 1 day, 95.0% at 1 year, and 93.9% at 10 years. Ten-year survival varied by condition, ranging from 36.9% for holoprosencephaly to 99.3% for pyloric stenosis. One-year survival was associated with increasing gestational age (e.g., increasing from 46.9% at <28 weeks to 95.8% at ≥37 weeks for spina bifida). One-year survival increased in more recent birth years for several defect categories (e.g., increasing from 86.0% among 1999-2004 births to 93.1% among 2014-2017 births for unilateral renal agenesis/dysgenesis) and was higher among infants with an isolated defect versus those with multiple defects.

Interpretation

This study describes short- and long-term survival outcomes from one of the largest population-based birth defect registries in the world and highlights improved survival over time for several conditions. Our results may lend insight into future healthcare initiatives aimed at reducing mortality in this population.

Funding

This study was funded in part by a Centers for Disease Control and Prevention (CDC) birth defects surveillance cooperative agreement with the Texas Department of State Health Services and Health Resources and Services Administration (HRSA) Block Grant funds.

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.

Factors associated with nonsyndromic anotia and microtia, Texas, 1999-2014

BACKGROUND

Few risk factors have been identified for nonsyndromic anotia/microtia (A/M).

METHODS

We obtained data on cases and a reference population of all livebirths in Texas for 1999-2014 from the Texas Birth Defects Registry (TBDR) and Texas vital records. We estimated prevalence ratios (PRs) and 95% confidence intervals (CIs) for A/M (any, isolated, nonisolated, unilateral, and bilateral) using Poisson regression. We evaluated trends in prevalence rates using Joinpoint regression.

RESULTS

We identified 1,322 cases, of whom 982 (74.3%) had isolated and 1,175 (88.9%) had unilateral A/M. Prevalence was increased among males (PR: 1.3, 95% CI: 1.2-1.4), offspring of women with less than high school education (PR: 1.3, 95% CI: 1.1-1.5), diabetes (PR: 2.0, 95% CI: 1.6-2.4), or age 30-39 versus 20-29 years (PR: 1.2, 95% CI: 1.0-1.3). The prevalence was decreased among offspring of non-Hispanic Black versus White women (PR: 0.6, 95% CI: 0.4-0.8) but increased among offspring of Hispanic women (PR: 2.9, 95% CI: 2.5-3.4) and non-Hispanic women of other races (PR: 1.7, 95% CI: 1.3-2.3). We observed similar results among cases with isolated and unilateral A/M. Sex disparities were not evident for nonisolated or bilateral phenotypes, nor did birth prevalence differ between offspring of non-Hispanic Black and non-Hispanic White women. Maternal diabetes was more strongly associated with nonisolated (PR: 4.5, 95% CI: 3.2-6.4) and bilateral A/M (PR: 5.0, 95% CI: 3.3-7.7). Crude prevalence rates increased throughout the study period (annual percent change: 1.82).

CONCLUSION

We identified differences in the prevalence of nonsyndromic A/M by maternal race/ethnicity, education, and age, which may be indicators of unidentified social/environmental risk factors.

Identifying syndromes in studies of structural birth defects: Guidance on classification and evaluation of potential impact

Structural birth defects that occur in infants with syndromes may be etiologically distinct from those that occur in infants in whom there is not a recognized pattern of malformations; however, population-based registries often lack the resources to classify syndromic status via case reviews. We developed criteria to systematically identify infants with suspected syndromes, grouped by syndrome type and level of effort required for syndrome classification (e.g., text search). We applied this algorithm to the Texas Birth Defects Registry (TBDR) to describe the proportion of infants with syndromes delivered during 1999-2014. We also developed a bias analysis tool to estimate the potential percent bias resulting from including infants with syndromes in studies of risk factors. Among 207,880 cases with birth defects in the TBDR, 15% had suspected syndromes and 85% were assumed to be nonsyndromic, with a range across defect types from 28.5% (atrioventricular septal defects) to 98.9% (pyloric stenosis). Across hypothetical scenarios varying expected parameters (e.g., nonsyndromic proportion), the inclusion of syndromic cases in analyses resulted in up to 50.0% bias in prevalence ratios. In summary, we present a framework for identifying infants with syndromic conditions; implementation might harmonize syndromic classification across registries and reduce bias in association estimates.