Part one provided a brief introduction (click here for part one). In this section some medical issues are discussed.
Medical Issues Associated with Preterm Births
When a baby is born before term most of its organs are immature; however, the brain and the lungs appear to be especially susceptible to the consequences of a birth before term. This inevitably results in high rates of long-term health and neurological issues for these children. Because there are increasing costs to provide for neonatal intensive care as well as increasing social and economic burdens of the disabilities associated with preterm births there is an ongoing debate concerning the notion if the use of intensive care is actually justifiable for preterm infants that have borderline viability. As survival rates increase clinicians will find themselves increasingly exposed to the survivors of preterm births. As a result physicians and other health care workers should be aware of the ever-changing outcomes of preterm births as well as the long-term effects of the disabilities associated with preterm births and the numerous health problems that are incurred on the survivors, their families, and on society Saigal & Doyle, 2008).
Neurological Problems
Neurological problems associated with preterm birth are numerous and include developmental disability, developmental delays, apnea of prematurity, retinopathy of prematurity, cerebral palsy, hypoxic-ischemic encephalopathy, and intraventricular hemorrhage. This last complication, bleeds within the ventricles of the brain, has been known to affect as many as 25 percent of preterm babies and is especially a problem if the baby is born before the 32nd week of pregnancy (Saigal & Doyle, 2008). Babies can be resilient and milder brain bleeds may not result in severe or lasting complications; however, more severe bleeds can result in severe irreparable brain damage or even death.
The HPA-axis
With respect to neurological issues in preterm infants, the thyroid gland, pituitary gland, and the hypothalamus all begin their development early in gestation. Berbel, Navarro, Auso, Varea, et al. (2010) investigated the role of the thyroid gland in brain development. At about 10-12 weeks thyroid hormone synthesis begins and serum thyroid hormone levels progressively rise progressively for the remainder of gestation. The hypo-thalamic-pituitary-thyroid axis (HPA-axis), that deals with stress, hormone regulation, and other functions, becomes functional in the infant during the latter half of gestation, but its development continues until nearly two months after birth in normal human infants. As a result, the developing infant requires thyroid hormones from the mother during its development in utero. Thyroid hormones are extremely important regulators of the infant’s brain development during the both the fetal and neonatal periods. During these periods these hormones control both neuronal and glial proliferation in specific brain regions and are important in regulating neural migration and neural differentiation. Neural differentiation also includes the development of neuronal connections and myelination which are crucial to normal development. This differentiation takes place in very discrete developmental periods or windows. Thus, the role of these thyroid hormones in coordinating the timing of specific developmental signals and events is critical and even transient disruptions in thyroid hormone availability can lead to very profound effects on the brain development of the infant. Some research has been able to link the neurodevelopmental problems associated with preterm birth to lack of maternal thyroid hormones as the immature infant’s thyroid gland cannot meet their own requirements.
Magnetic Resonance Imaging (MRI) can be useful to identify the structural abnormalities of the preterm infant’s brain. However, in many developmentally delayed children MRI cannot determine any structural difficulties and other more sensitive methods must be used. For example, Filippi, Ulug, Deck, Zimmerman, and Heier (2002) in a seminal study reported results of using Proton MR Spectroscopy to detect differences in brain myelination of normal children to developmentally delayed children over the age of two years that had normal MRI scans. Children under age two with delays did not yet demonstrate this difference. Consequently, preterm children may have subtle differences in their brains not readily observed by conventional assessment techniques and the researchers suggested using different methods to search for these etiologies.
Other Medical Issues
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).
Neurodevelopmental Sequelae
Cerebral Palsy
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).
Over 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 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
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 mentally 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).
Click here to read Part III: Cognitive and other Behavioral Problems
Rudy Hatfield - I am a clinical neuropsychologist with extensive experience in the assessment and treatment of neurological and psychiatric disorders. I ...
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