Birth Defects

Definition of Reported Measures

  • Anencephaly occurs when the portion of neural tube that forms the brain does not close during the first weeks of pregnancy.
  • Cleft lip with cleft palate occurs when the structures that form the infant’s lip and roof of the mouth do not fully close during development.
  • Cleft lip without cleft palate occurs when the structures that form the infant’s lip do not fully close during development.  
  • Down Syndrome (Trisomy 21) occurs when the egg or sperm divides incorrectly, so that the infant has an extra copy of chromosome 21.
  • Gastroschisis occurs when a portion of the infant's intestines protrude through the body, typically next to the umbilical cord.
  • Hypoplastic left heart syndrome is a term for a group of defects, indicating that the left side of heart is underdeveloped.
  • Hypospadias (male infants only) occurs in males when the opening of the urethra, the tube that carries urine from the bladder to the outside of the body, is located along the underside of the penis instead of at the tip.
  • Limb deficiencies occurs when part of the fetal arm, leg, lower or upper limb do not form completely during pregnancy.
  • Spinal bifida without anencephaly occurs when the portion of the neural tube that forms the spinal cord does not close completely during weeks 3 and 4 of pregnancy.
  • Tetralogy of Fallot is present at birth and affects the flow of blood through the heart.
  • Transposition of the great arteries (vessels) occurs when the two main arteries carrying blood away from the heart (the pulmonary artery and the aorta) are switched or transposed in position.

How to Read Tables, Charts, and Maps

  • The 95% confidence interval (CI) is the range of values that likely contains the true rate in the population.
  • Prevalence rates express the number of outcomes over a specific time period relative to the number of live births for that same time period.  N/A indicates that the data are not available due to the number of events being less than 5.
  • Average number per year are listed next to prevalence rates unless the total number of events is less than 5

Data Sources

  • The California Birth Defects Monitoring Program, California Department of Public Health. The California Birth Defects Monitoring Program only conducts routine surveillance in eight counties located in the Central Valley: Fresno, Kern, Kings, Madera, Merced, San Joaquin, Stanislaus, and Tulare.

Methods

  • Average- The 4 or 5-year average is calculated by counting the total number of a particular birth defect (e.g. anencephaly) over the time period (e.g. 2010-2014) and dividing by the number of years presented.
  • Prevalence Rate- The 4 or 5-year prevalence rate for each birth defect is calculated by taking the total number of a particular birth defect over a specific time period (e.g. 2010-2014) in a county, and dividing by the total number of live births in that county for that same time period.  The rates are then multiplied by 10,000 and expressed as X birth defects per 10,000 live births.

Limitations

  • Data are only available for: Fresno, Kern, Kings, Madera, Merced, San Joaquin, Stanislaus, and Tulare. These are the only counties currently being monitored for birth defects by the California Birth Defects Monitoring Program. Thus statewide data or data for counties other than the aforementioned eight do not exist.
  • Data are aggregated into 4 or 5-year intervals. Birth defects are a rare event.  In order to analyze demographic sub-groups of data, while protecting confidentiality, we have aggregated the data into multi-year intervals

Suggested Citation

Tracking California, Public Health Institute. Birth Defects data. Accessed [Month/Day/Year] from www.trackingcalifornia.org/cbd/query.


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