While neurological issues delays are primarily responsible for the functional developmental delays in children other complications can also affect the development of a preterm child. These problems include: cardiovascular complications; respiratory problems such as respiratory distress syndrome or chronic lung disease; a number of severe metabolic and gastrointestinal problems that can result in delayed growth and other problems; immune system problems, such as susceptibility to infections or diseases like pneumonia; and hematologic complications (Saigal & Doyle, 2008).
Cerebral palsy is a heterogeneous group of neurologically-related disorders that can involve central nervous system functions as well as other functions such as leaning, movement, vision, hearing, and cognitive speed (Saigal & Doyle, 2008). As a result there are several variations of cerebral palsy including dyskinetic (mixed tone in the muscles that leads to difficulties with posture and movement), spastic (increased muscle tone leading to stiff and jerky movements), ataxic (poor coordination and loose/low muscle tone leading to floppy movements), and mixed (two or more of the other types are present).
Across most studies the incidence of cerebral palsy in preterm children is negatively related to weeks of gestation, although some studies indicate curvilinear trends (Saigal & Doyle, 2008). Therefore, both the prevalence and severity of cerebral palsy in preterm infants will general ly vary depending on the time to birth. For instance, Sagial and Doyle (2008) report the results of some Swedish studies that indicated that the rates of cerebral palsy were 14%, 19%, and 3% for infants born at 23-24, 25-26, and 27 weeks of gestation respectively. .
A significant number of children who are born preterm develop cerebral palsy. Many of these children have moderate to severe motor disabilities. These disabilities obviously lead to delays in motor and even sensory development (Marlow, Wolke, Bracewell, & Samara, 2005; Sagial & Doyle, 2008). Children with either moderate or severely disabling cerebral palsy are significantly more likely to display cognitive impairments when compared to age-matched normal peers as well as children with other motor problems (Sagial & Doyle, 2008). Marlow, Wolke, Bracewell, & Samara (2005) performed a large and often cited study of very early preterm infants who were six years of age and compared them to their full term peers on their performances over several cognitive measures. Overall performance was significantly lower for children with cerebral palsy for children without neurological abnormalities. Moreover, the cognitive scores of the very preterm children who later display cerebral palsy are typically poorer than those who are born preterm but at a longer weeks of gestation. Forty six percent of children born between 22 and 25 weeks of gestation had severe or moderate disabilities such as cerebral palsy, vision or hearing loss, and learning problems.
Mental retardation is not uncommon for preterm infants. Like cerebral palsy there is an inverse relationship between the weeks of gestation to birth and the prevalence and severity of mental retardation in preterm infants (Sagial & Doyle, 2008). Using the United States criteria for mental retardation (IQ < 70) Neubauer, Voss, and Kattner (2008) found a high proportion of mental retardation in a cohort of preterm infants that had been treated at a neonatal intensive care unit and followed up to age ten. The researchers defined a major impairment present in the child if the child had one or more of the following: cerebral palsy, intellectual disability, blindness, deafness, and/or intractable epilepsy. In the cohort of 135 children 24 had major impairment as defined by the researchers and of those 24 children 19 (79%) had mental retardation. The researchers did not delineate the various IQ scores of this subset of children so there is no way of knowing the range of mental impairment observed in the cohort; however, they did report that earlier preterm infants were more likely to have more severe deficits.
Given the aforementioned discussion concerning the role of the thyroid in assisting with cerebral development the finding of high levels of mental retardation in this group is not surprising.
Other Motor and Sensory Disabilities
Although individual differences can vary significantly among both full term and preterm children regarding their capacity to respond to environmental stimuli, preterm infants demonstrate some rather striking differences. Preterm infants have been observed to spend less time in a state of awareness than full term infants. They sleep more than full term infants and when they are alert they often experience difficulty maintaining states of alertness or wakefulness (Sagial & Doyle, 2008). Preterm infants also appear less responsive to sights and sounds around them. Motor development is often delayed, especially in the second half of the first year when many parents report that noticeable changes in a preterm infant's motor abilities are often reported (Restiffe & Gherpelli, 2006; Marlow, Wolke, Bracewell, & Samara, 2005).
Less severe motor disabilities can also lead to developmental delays in children; however, some studies have suggested that correcting for the age of the child (taking into account the child's age from conception opposed to birth) often leads to a more valid assessment of the child's development as opposed to using age measurements from birth (Restiffe & Gherpelli, 2006). Moreover, male children appear more likely than female children to display motor difficulties. In addition, many of the differences in motor skills not related to severe neurological problems such as cerebral palsy diminish significantly and even dissipate as the child gets older. Often by age two and beyond these differences are not apparent. Thus, there is a significant body of research that has argued that comparisons between preterm infants and full term infants, at least concerning mild forms of motor disabilities, should not be made (Restiffe & Gherpelli, 2006).
The effects of early environment on the development of the preterm infant regarding their sensory and motor skills and development has been investigated by many researchers (e.g., see Beck et al., 2010; Sagial & Doyle, 2008). From these studies it is clear that the special or different environment of the preterm infant lead to markedly different social interactions between the infant and its caregiver when compared to full term infants. Studies have indicated that when preterm infants are stimulated either by rocking or by using visual or auditory stimulation they demonstrate greater gains in body weight and overall development compared to the preterm infants who do not receive these special treatments (Beck et al., 2010). Thus, at least some of the long-term consequences of preterm birth may be offset by the use of careful monitoring and by the use of intervention programs that support an educate parents about the most productive way to care and stimulate these frail infants (Restiffe & Gherpelli, 2006; Sagial & Doyle, 2008).
Cognitive and other Behavioral Sequelae
Deficits in Intelligence
Even though the majority of children even born at fewer than 26 weeks of gestation often have cognitive and IQ scores within the lower average ranges there are still some interesting trends in the research regarding the cognitive performance of preterm children.
This paper has already discussed the potential for preterm infants to qualify for a diagnosis of mental retardation; however, even preterm children that do not have major impairments demonstrated lower than expected IQ attainment. This is important because aspects of intelligence have been demonstrated to be a major factor associated with developmental delays in children (Marlow, Wolke, Bracewell, & Samara, 2005).
Sagial and Doyle (2008) report studies that indicate that infants born before 28 weeks of gestation when tested at eight years of age scored poorer than controls of normal birth weight on measures of full-scale IQ. The magnitude of the difference between the two groups was between a half and three quarters of a standard deviation suggesting that the difference in IQ general abilities and not specific intellectual abilities
Marlow, Wolke, Bracewell, & Samara (2005) compared IQ attainment of extremely preterm children born before 25 weeks of gestation to normal term children at six years if age. The mean difference in the scores for overall cognitive ability (IQ) between the extremely preterm group and the control group of classmates was 24 IQ points with a 95% confidence interval of 20 to 27 IQ points. This is an amazing large difference
. In the control classmate group the IQ scores of the boys were not significantly different from the IQ scores of the girls; however, among the extremely preterm group the boys had a mean difference of 10 IQ points lower than the girls. In an ANOVA analysis the interaction between sex and group was highly significant (p = 0.002). The researchers decided that perhaps physical disabilities could confound the results, but the effects remained robust even after the exclusion from the analysis of children with physical disabilities (a mean difference of 20 IQ points and a 95% confidence interval of 17 to 23 IQ points. Although there also appeared to be a significant decrease in the…