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Birth Defects

Maternal Conditions

Birth defects can also result from physical conditions affecting the health of the mother. One common maternal condition associated with birth defects is diabetes mellitus, a multifactorial disorder. Mothers with diabetes have a two-to three-fold times greater risk of having a child with birth defects than the general population if their condition is not well controlled. However, good glucose control has been shown to correlate with a decreased risk of congenital malformations. Characteristic diabetic malformations include cardiovascular, craniofacial, genitourinary, gastrointestinal, and neurological abnormalities. The risk that the child born of a mother with diabetes mellitis will also develop diabetes as an adult is 1 to 3 percent.

Another maternal condition giving rise to birth defects is maternal phenylketonuria (PKU). This is an autosomal recessive disorder in which an enzyme called phenylalanine hydroxylase is defective. This enzyme normally converts a substance in the blood called phenylalanine to another substance called tyrosine. As a result, phenylalanine levels are high, resulting in mental retardation, microencephaly, growth retardation, cardiac problems, seizures, vomiting, and hyperactivity. Other traits associated with PKU are fair hair and skin and blue eyes. PKU can be effectively managed through changes in the diet, and women who have appropriately managed their diet can have pregnancies with healthy offspring.

Nancy S. Green

and Terri Creeden


Batshaw, Mark L. When Your Child Has a Disability: The Complete Sourcebook of Daily and Medical Care. Baltimore, MD: Paul H. Brooks Publishing, 2001.

"Leading Categories of Birth Defects." March of Dimes Perinatal Data Center, 2000.

Internet Resource

National Organization of Rare Disorders. <http://www.rarediseases.org>.

The average IQ of an individual with Down syndrome is 55. Most tests cite an IQ of 100 as "average."

Additional topics

Medicine EncyclopediaGenetics in Medicine - Part 1Birth Defects - Various Causes, Various Treatments, Single-gene Mutations, Autosomal Dominant Disorders, Functional Birth Defects