Possible Causes for Developmental Delays
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.
A mother who does not appear to respond to her child's cries or smiles is one example of unresponsive behavior that may affect the level of infant stimulation. This type of response is more likely to occur after an unwanted pregnancy, when the mother has a serious or chronic illness, or while the mother is addicted to alcohol or other drugs (Evrand & Scola, 1990). It is also likely to occur when a infant has a disability that lowers the child's level of responsiveness, which in turn leads to the adults being less responsive. See Table 3.2 for a list of postnatal medical complications that also place children at risk.
Many environmental conditions believed to contribute to developmental delays are related to the socioeconomic status (SES) of children's families (Wachs & Gruen, 1982). That is, children from lower SES families are believed to be more vulnerable or more at risk than other children. This risk status may occur because low SES mothers often lack adequate prenatal care and are more likely to give birth to low birth weight children. Children with exceptionally low birth weight tend to have lower intelligence quotient (IQ) scores when evaluated later in life. Low birth weight is also related to higher rates of seizures, mental retardation, cerebral palsy, and deafness (Bennett, 1984).
Children from low SES families are also less likely to have adequate medical care, including lack of immunizations, and may be malnourished. Lead poisoning. which is linked to mental retardation and learning disabilities, is more likely to be found in the homes of low SES families. These children are also more likely at risk because of the increased likelihood of having family members with histories of diabetes, muscular dystrophy, epilepsy, or hearing problems. Children from low SES backgrounds are more likely to be exposed to drugs, alcohol, and human immmunodeficiency virus (HIV) prenatally, which also places them at risk (Herbst & Baird, 1983).
Many children classified as developmentally delayed come from diverse cultural backgrounds and may be exposed to bilingual home environments (Hakuta & Garcia, 1989). Often, it is difficult to provide a nonbiased assessment of children from diverse backgrounds. This may be because it is difficult to find professionals who speak English as well as the language most often spoken in the child's home. Research indicates that children from varied cultures may be labeled as developmentally delayed, even when they are not, based on aptitude tests that are often biased against children from minority cultures (Capron & Duyme, 1989).
It is often difficult to separate effects of multiculturalism from effects of poverty. A disproportionate number of culturally diverse children live in poverty. The National Council on Disability (1993) reported that 53 percent of African American families and 40 percent of Latino families live in poverty. This is in contrast to this organization's estimate that about 22 percent of all American children live in poverty.
There are many factors that place children at risk of developmental delays. The goal of early intervention programs is to help prevent delays from occurring by providing proper nutrition, medical care, and healthy learning environments. Data from several infant and preschool intervention programs suggest that these programs are one of the most successful ways to compensate for the effects of poverty on children's later development (Campbell & Ramey, 1991).
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