Birth Defect Clusters

What is a birth defect cluster?

  • A birth defect cluster is the occurrence of more than the usual or expected number of birth defect cases in a specific geographical area during a defined period of time.

What causes clusters?

  • Birth defects, like all other health conditions, often occur in clusters.
  • Most happen by coincidence or chance alone.
  • Others can be explained by changes in diagnostic practices or hospital referral patterns.
  • Rarely, a cluster is due to an environmental exposure that all the mothers or fathers have in common. 

Why investigate birth defect clusters?

  • The purpose of evaluating cluster reports is to determine if an increase in birth defects has occurred and, if so, whether there is an exposure that may be linked.
  • A cluster investigation cannot answer parents' questions about why their child was born with a birth defect. Causes can only be identified through large case-control interview studies, like the National Birth Defects Prevention Study.

What characterizes a cluster caused by environmental exposure?

Evidence includes:

  • A large increase in babies born with the same birth defect and
  • A prenatal exposure that the mothers or fathers have in common, such as illness, diet, medication, alcohol or drugs, or chemicals at home or work.

Who should I report a cluster to?

  • Suspected clusters should be reported to the public health officer in your county health department or the state department of health.

What information should I include in a cluster report?

To evaluate the report, investigators need to know:

  • For each child, the names of the mother and baby, the date and hospital of birth, and all the child's diagnoses,
  • Ideas about environmental exposures during early pregnancy. To determine if the cases may have the same cause, investigators need to know what exposures all the mothers have in common.

What about the confidentiality of the information I provide?

  • State law requires that all identifying information be kept confidential.
  • Only investigating staff have access to this information
  • Public reports are limited to summary data.

What will happen after I make a report?

Investigators will determine:

  • If all the babies have the same birth defect
  • Whether there are more babies with the same birth defect than would normally be expected in a certain area for a certain period (many conditions are more common than people realize).
  • If there is a common exposure that may explain the increase.
  • Parents may be asked to provide more information and to give permission for investigators to review their medical records.
  • A written report will be made of the investigation's findings.

Birth Defect Cluster Investigations in Texas 

For more information or possible cluster concerns, please email

The information above was adapted with permission from the National Birth Defects Prevention Network.