About 80% of birth defects between 2005 and 2009 have an unknown etiology, according to a study published in the BMJ.

Marcia L. Feldkamp, Division of Medical Genetics, Department of Pediatrics, University of Utah School of Medicine, and colleagues sought to assess causation and clinical presentation of major birth defects in children born between 2005 and 2009 to resident women in Utah’s statewide population-based public health surveillance system.

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The study included 5,504 cases among 270,878 births (prevalence 2.03%), excluding mild isolated conditions such as muscular ventricular septal defects and distal hypospadias. Results showed that 92.1% were live born infants, and 75.3% of cases (either known or unknown etiology) were classified as having an isolated birth defect.

The researchers observed a definite cause of birth defect in 20.2% of cases (n=1,114). Chromosomal or genetic conditions accounted for 94.4% of known birth defects, teratogens for 4.1%, and having twins for 1.4%.

The remaining 79.8% (n=4,390) were classified as unknown etiology, and 88.2% of these were isolated birth defects. A family history, defined as a similarly affected first-degree relative, was documented in 4.8%.

“For clinicians and parents, it is important to understand what can be done today to prevent birth defects, in particular the role of preconception care focusing on optimal women’s health (including screening/treating chronic illnesses, attaining folic acid sufficiency, etc),” the study authors wrote.

“In addition, investigation of potential causes of a birth defect at the time of diagnosis (such as whether a genetic condition is present) can help to better plan management and appropriately counsel families, including the relief of anxiety related to unfounded information and guilt,” the researchers concluded.


  1. Feldkamp ML, Carey JC, Byrne JLB, Krikov S, Botto LD. Etiology and clinical presentation of birth defects: Population based study. BMJ. 2017. doi:10.1136/bmj.j2249