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epidemiology


The registry—a system for recording and tracking malformations in the population—is the backbone of birth defects epidemiology. The California Birth Defects Registry is a database of diagnostic and demographic information drawn from over 3.9 million births. Our data collection and reporting procedures—reflecting 20+ years experience—ensure that data is accurate, comprehensive, consistent and useful.

WHO’S IN THE REGISTRY?

We gather information on children with specified birth defects— major malformations with significant medical and public health impact. We look at live births, medically indicated pregnancy terminations, and stillbirths occurring after 20 weeks gestation.

Our registry covers a representative subset of California counties—Fresno, Kern, Kings, Madera, Merced, Orange, Riverside, San Bernardino, San Diego, San Joaquin, Stanislaus and Tulare—comprising 44% of the state’s births and reflecting its racial/ethnic diversity. (Limited data collection occurs in additional counties for research purposes.)

COLLECTING MEDICAL INFORMATION

We use broad casefinding criteria following well-documented procedures to ensure complete ascertainment. Program staff review logbooks and other records at hospitals where births occur or where children are treated, as well as genetic clinics and chromosome laboratories.
Data collection specialists review the entire medical chart for each potential case identified, recording any diagnoses made prenatally, after birth and up to 1 year. Only conditions confirmed by physicians using appropriate tests (for example, x-rays, cardiac catheterization, surgery, autopsy) are included. Since 1998, medical geneticists—specialists in birth defects—have evaluated case records to ensure diagnostic criteria are met.

LINKING WITH VITAL STATISTICS RECORDS

Information is coded and entered into the database. We merge multiple records on the same child, who may have been treated at several facilities or had many hospital admissions. Case files are linked to Vital Statistics records (birth or fetal death certificates) which supply demographics, including parents’ races, ages, and residence.

ANALYZING AND REPORTING RESULTS

To minimize the random variation inherent in small numbers, we report:

bullet 5 year averages
bullet Estimated figures for counties derived from registry rates and local population size.

To protect confidentiality, we do not report:

bullet Rates based on fewer than 5 cases
bullet Potentially identifying information.

SAFEGUARDING CONFIDENTIALITY

We have a moral and legal obligation to protect and keep confidential all information that could potentially identify children or their families.

Confidentiality Requirements and Procedures



WHAT MAKES THE REGISTRY UNIQUE?

bullet Population-based ascertainment. We actively gather data rather than relying on physician or hospital reporting, and cast a wide case-collection net to identify all eligible children within our registry areas.
bullet Robust medical data. We gather complete diagnostic information on eligible children, including confirmatory clinical tests. Specialists in birth defects review case records.
bullet One year follow-up. Although many birth defects are not correctly diagnosed in the newborn period, approximately 95% are recognized by a child’s first birthday.
bullet Large and varied population. The registry reflects California’s racial/ethnic diversity, providing unique data on never-before studied groups such as the Vietnamese.

HOW IS THE DATA USED?

Registry data can be mined for a variety of activities:

bullet Surveillance—monitoring baseline rates/trends.
bullet Supporting research studies—suggesting clues for further study, identifying cases and controls.
bullet Planning services—evaluating public health programs.
bullet Addressing public concerns—about birth defects and the environment.

REFINEMENTS OVER TIME

Over 20 years of experience have taught us:

bullet Bigger isn’t necessarily better. We began by collecting statewide information on 200+ conditions, many of which were rare or unevenly diagnosed or ascertained. This provided valuable baseline information, but studying such data wasn’t always productive.
bullet Better data is more useful. To maximize our effectiveness, we now focus on gathering pristine data on conditions with medical and public health impact—about 60% of newborns with birth defects has at least one of our registry conditions.
bullet Research studies are the best way to find causes. Widespread population monitoring did not identify any environmental agents causing birth defects. Large-scale studies are more effective in pinpointing causes and subtle risk factors.




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