The California Birth Defects Monitoring Program is capable of springing into action when there is concern that local environmental conditions may be linked to birth defects. Small area investigations can be reactive or proactive, responding to community cluster reports or an environmental emergency.
INVESTIGATING BIRTH DEFECTS CLUSTERS
A cluster is a mini-epidemic, where too many affected babies are born in a short time span. Birth defects, like other health conditions, often occur in clusters. Most happen by coincidence or chance alone. Others can be explained by changes in medical practices. Very rarely, a cluster is due to a teratogen—an environmental exposure that causes birth defects.
IN THE AFTERMATH OF AN ENVIRONMENTAL CRISIS
Occasionally, an environmental emergency prompts concerns. For example, in 1991, The Program tracked over 100 pregnancies conceived shortly before or after a massive spill of the toxic herbicide metam-sodium into the Sacramento River. (We determined that birth defects were not elevated.)
HALLMARKS OF A TERATOGEN
A local investigation can only detect “sledgehammers”–very potent teratogens. Otherwise, the limited numbers involved aren’t statistically powerful enough to resolve questions. At best, small area studies generate clues—even if results are suspicious, they must be confirmed with a larger case-control study.
In evaluating community concerns, we look for the features noted in scenarios where teratogens have been involved:
- cases with the same or developmentally related birth defects
- a large increase (more than 10 times the expected rate)
- an exposure in common.