Possible Causes for Developmental Delays

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About 10 percent of all infants, toddlers, and preschool children are classified as developmentally delayed (U.S. Department of Education, 1995). Possible causes for developmental delays are numerous. They are categorized as genetic influences inherited from biological parents and environmental influences, including accidents, exposure to toxins, illnesses, and cultural disadvantages such as being raised in poor living conditions. Delays based on genetic influences are estimated to account for about 15 to 25 percent of developmental disorders. About 75 to 85 percent of these cases are linked to effects of the environment or the reasons for developmental delays remain unknown (Bee, 1995).

Factors that affect physiological causes may be referred to as biological causes. Biological factors may be based on environmental or genetic influences. Infections, lead poisoning, head injuries, and prenatal exposure to toxins are a few of the many possible environmental effects that may result in physiological abnormalities. Inherited disorders such as metabolic conditions (e.g., PKU) or syndromes (e.g., fragile-X) are examples of genetic factors that contribute to biological changes.

Although causes for developmental delays often are not clearly determined and every child has a unique pattern of delay, certain characteristics are associated with particular disabilities. These characteristics are described in this chapter. To help prevent developmental delays from occurring, it is first necessary to develop an understanding of factors that place children at risk.

While children from all socioeconomic groups of society are known to have developmental delays, some children appear to be more vulnerable than others (Kendall, 1996). Children who live in environments believed to lower the likelihood of reaching maximum levels of development are often referred to as at risk or high risk. These children have a higher than normal probability of having a developmental delay. Although there is no single set of indicators identifying children as being at risk for a developmental delay, there are several situations or characteristics that suggest children are at risk (Ramey & Campbell, 1984). See Table 3.1 for a list of environmental conditions that may place children at risk.

Prenatal factors, conditions that occur during pregnancy such as Rh incompatibility (blood incompatibility), viral infections, toxemia (toxic substances in the blood), and exposure to drugs may place children at risk. Perinatal factors, conditions that occur during the birth process, including labor and delivery, may also contribute to abnormal development. Prolonged labors lasting more than twenty-four hours or difficult labors may lead to head injuries or lack of oxygen for the child. In addition, children with low birth weight and who are born prematurely, after less than thirty-seven weeks in the womb, are also considered to be at risk for developmental delays (Thurman & Widerstrom, 1990).

After birth, a number of medical complications or postnatal factors may place a child at risk. One postnatal factor is maternal deprivation. It occurs when mothers or mother figures behave in an emotionally unresponsive fashion toward their children. In the case of maternal deprivation, children often receive very limited stimulation. Sensory stimulation is crucial for optimal development of the infant.