Perception of Child Vulnerability Among Mothers of Former Premature Infants
* Departments of Pediatrics
Public Health Sciences, Wake Forest University School of Medicine, Winston-Salem, North Carolina
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ABSTRACT |
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Objectives. Parents of premature infants often perceive their infants as medically vulnerable. High parental perception of child vulnerability (PPCV) is associated with disproportionately high health care utilization. The objectives of this study were to determine whether higher PPCV is correlated with worse developmental outcome in premature infants at 1-year adjusted age and to identify factors, present at neonatal discharge, that predict high PPCV.
Methods. This prospective cohort study assessed mothers of 116 premature infants who were 
32 weeks’ gestation and required supplemental oxygen at 36 weeks postmenstrual age. At neonatal discharge, mothers completed the Spielberger State Anxiety Inventory, Beck Depression Inventory, Impact on Family Scale, Life Orientation Test, General Health Survey, and Medical Outcomes Study social support survey. At 1-year adjusted age, child development was assessed using the Bayley Scales of Infant Development and Vineland Adaptive Behavior Scales, and mothers completed the Vulnerable Child Scale, a 16-item self-report measure of PPCV. Chart review was performed to determine the presence or absence of specific indicators of medical vulnerability at 1-year adjusted age.
Results. Mean infant gestational age and birth weight were 26.5 ± 2.5 weeks and 894 ± 287 g. A total of 69% of mothers were white, and 78% were high school graduates. Higher PPCV (lower Vulnerable Child Scale score) was correlated with lower scores on the Vineland Adaptive Behavior Composite and Bayley Psychomotor Developmental Index but not on the Bayley Mental Developmental Index. After controlling for the presence of 1 or more indicators of medical vulnerability, higher PPCV was still correlated with lower adaptive development. This correlation was stronger in the group of children with no indicators of medical vulnerability. In univariate analyses, higher PPCV was predicted by nonfirstborn status; longer neonatal hospitalization; higher maternal anxiety and depression; greater impact of the illness on the family; and lower maternal optimism, life satisfaction, and social support. PPCV was not associated with maternal age, education, marital status, income, or ethnicity or with child gender, gestational age, birth weight, or length of mechanical ventilation. A linear regression model containing all variables significant at the univariate level explained 29% of the variance in PPCV. Maternal anxiety was the only variable that was statistically significant in the full model.
Conclusions. Higher PPCV is associated with worse developmental outcome in premature infants at 1-year adjusted age. Maternal anxiety at neonatal discharge predicts later high PPCV. Interventions to prevent or decrease PPCV in premature infants should be targeted at parents who are more anxious at hospital discharge.
Key Words: vulnerable child syndrome • parental perceptions • vulnerability • prematurity
Abbreviations: PPCV, parental perception of child vulnerability • VCS, Vulnerable Child Scale • ABC, Adaptive Behavior Composite • MDI, Mental Developmental Index • PDI, Psychomotor Developmental Index
Children who are perceived by their parents as vulnerable have an increased risk of behavior problems, difficult parent–child interactions,1–3 and disproportionately high health care utilization.4–6 In their original description of the vulnerable child syndrome, Green and Solnit7 recognized that children who experience an acute, potentially life-threatening illness early in life may be perceived by their parents as being medically vulnerable long after they have fully recovered. This heightened parental perception of child vulnerability (PPCV) was hypothesized to have long-term negative effects on the parent–child relationship, leading to problems with separation, discipline, academic underachievement, and excessive health concerns. Thomasgard and Metz8 defined PPCV as "an increased parental perception of child vulnerability to illness or injury, secondary to separation or loss, which is either real or feared." Children whose mothers view them as vulnerable are more likely than their peers to be rated by their mother as having somatic problems, social withdrawal, and behavior problems.1–3,9 Mothers who see their children as vulnerable feel less competent at parenting and less in control of their children’s behavior.1 They also identify their children as less developmentally competent than do medical providers or objective measurements of cognitive development.1 High PPCV is associated with increased use of health care resources, including more frequent sick, well-child, and emergency department visits.2,4,5,9–11
Parents of premature infants often perceive their infants as medically vulnerable, even after their health improves.1,3,12 Among the recognized antecedents of high PPCV,7,8,13,14 premature birth is particularly important because of the dramatic increase in the survival rates of premature infants over the past decade.15 Premature infants often have multiple risk factors for high PPCV: pregnancy complications,16 maternal depression,16 jaundice,4 feeding and crying behavior,9 and/or parental worry that the child might die.2,9,13 Parents of sick premature infants are faced with the possibility of serious morbidity and/or mortality of their infants. Therefore, it is not surprising that 64% of preschoolers who were born prematurely are still perceived by their mother as vulnerable.1
If parents of premature infants who are more likely to develop high PPCV could be identified during the first months of a child’s life—before PPCV has developed—then interventions could be targeted toward their parents to prevent PPCV. Health care providers could help parents to develop more realistic expectations about their infants’ recovery and stress the need for the parents to treat their premature infants as normally as possible.7 Parents could also be given information about supportive counseling, parent support groups, and/or mentoring by experienced parents. These interventions might decrease the child behavior problems, parent–child interaction problems, and unnecessary health care utilization attributable to high PPCV.
Because most previous studies of PPCV have used cross-sectional designs, they have not been able to examine temporal relationships between risk factors and high PPCV. Studies of PPCV in premature infants have involved small samples.1,3,17 Little attention has been paid to the effects of maternal psychosocial factors on the later development of PPCV.8 Finally, the few studies that have assessed the relationship between PPCV and development or maternal perception of development have not assessed adaptive or motor development.1,18 This study addresses these issues.
The study had 2 objectives: 1) to determine whether higher PPCV is correlated with worse developmental outcome in premature infants at 1-year adjusted age and 2) to identify demographic, neonatal illness severity, and maternal psychosocial factors, present at neonatal discharge, that predict high PPCV.
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METHODS |
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Subjects
This prospective cohort study was part of a larger randomized clinical trial assessing outcomes of premature infants who were randomized to receive either community-based or center-based care after neonatal discharge. Infants were eligible for the study when they were born at
32 weeks, had chronic lung disease (defined as the need for supplemental oxygen at 36 weeks postmenstrual age), and were admitted to 1 of 5 intensive care nurseries in northwest North Carolina. Infants were excluded when they had a congenital lung or brain malformation, a tracheostomy, or a mother who did not speak English or who lived >150 miles away. Study infants were born between March 30, 1996, and March 17, 1998. The study was approved by the Institutional Review Board of Wake Forest University School of Medicine. Of 164 families consecutively approached about the randomized clinical trial, 150 (92%) agreed to participate in the study. A total of 146 children survived to 1-year adjusted age, and of these, 116 (79%) mothers completed questionnaires from which data for this study were derived. Participants and eligible nonparticipants did not differ on maternal and child demographic characteristics or indicators of neonatal illness severity. No differences were found between mothers of infants who were randomized to community-based and center-based follow-up in the larger trial on demographic factors, indicators of neonatal illness severity, maternal psychosocial factors, or parental perception of child vulnerability. Therefore, the 2 groups were combined for all analyses.
Procedures
Demographic and medical data about the infant (gender, birth weight, gestational age, length of mechanical ventilation, length of neonatal hospitalization, and medical complications) were collected by reviewing medical records. Demographic and psychosocial data about the mother (maternal age, marital status, ethnicity, education, anxiety, depression, optimism, life satisfaction, and social support) and the family (number of siblings, family income, and impact of the illness on the family) were collected using questionnaires completed by the mother in the week before discharge from the intensive care nursery. At 1-year adjusted age (adjusted for prematurity), maternal perception of child vulnerability and infant developmental outcomes were assessed in the Intensive Care Nursery Follow-up Clinic. Chart review was performed to determine the presence or absence of specific indicators of medical vulnerability at 1-year adjusted age.
Measures
Maternal perception of child vulnerability was assessed using the Vulnerable Child Scale (VCS),3 a 16-item measure that asks parents to respond to statements about their child’s health on a 4-point scale. Each item is scored from 1 ("definitely true") to 4 ("definitely false"). Lower scores indicate greater perception of vulnerability. Sample items include, "I feel anxious about leaving my child with a babysitter or at day care," and, "I sometimes worry that my child will die." The VCS has good internal reliability (Cronbach’s 
= .75). The scale has excellent test-retest reliability, both between telephone and mailed administrations (r = .95) and 2 telephone administrations (r = .96). The validity of the VCS is supported by its significant correlation with scores on the Internalization Somatic Symptoms subscale of the Personality Inventory for Children.3 The content of the VCS is relevant to parents of both infants and preschoolers. Since its original standardization on parents of preschoolers, reliable results have been obtained using the VCS with parents of infants as young as 3 months of age.19 Our study shows that the VCS has good internal reliability in parents of children at 1-year adjusted age (Cronbach’s = .82).
Maternal state anxiety was measured with the Spielberger State Anxiety Inventory, Form Y-1.20 Subjects are given 20 brief statements and asked to rate the intensity of their feelings of anxiety "right now/at this moment" on a 4-point scale, from "not at all" to "very much so." Typical items include, "I feel upset," and, "I am relaxed." Higher scores indicate greater state anxiety. The scale has good construct validity, discriminating adults with generalized anxiety disorder.20
Maternal depressive symptoms were assessed with the Beck Depression Inventory,21 a 20-item measure, for which Cronbach’s has been .73 to .92 and test-retest reliability has ranged from .48 to .86. Each of the 21 items is scored from 0 to 3, with higher scores reflecting more depressive symptoms. The measure correlates well with clinical ratings22 and the Hamilton Psychiatric Rating Scale for Depression.23
Maternal optimism was measured using the Life Orientation Test, a scale measuring dispositional optimism.24 This measure consists of 8 items and 4 filler items, scored from 0 ("strongly disagree") to 4 ("strongly agree"), with higher scores indicating higher optimism. Sample items include, "I always look on the bright side of things," and, "If something can go wrong for me, it will." The Life Orientation Test has adequate internal consistency (Cronbach’s = .76) and good test-retest reliability of .79. It also has adequate convergent validity, with factors that are distinct from conceptually similar variables measured by other scales.24
Maternal life satisfaction was measured using the first item of the General Health Survey.25 This item, known as the "Ladder of Life," is an analog scale on which respondents rate their life satisfaction over the past 4 weeks on a scale from 1 ("worst life I could expect to have") to 9 ("best life I could expect to have").25
Maternal social support was measured with the social support survey developed for the Medical Outcomes Study.26 This 19-item, self-report measure assesses the availability of 4 dimensions of social support: emotional/information, tangible, affectionate, and positive social interaction. Items are scored from 1 ("none of the time") to 5 ("all of the time"). Sample items include "someone who understands your problems" and "someone who shows you love and affection." Item scores are averaged and then transformed to yield total scores ranging from 1 to 100, with higher scores reflecting greater availability of social support. The measure has excellent internal reliability, with a Cronbach’s of .97. Its construct validity is evident in its high correlation with a measure of loneliness (r = –.67) and low correlation with a measure of physical functioning (r = .11).26
Impact of the illness on the family was assessed with the Impact on Family Scale,27 which measures the impact on 4 components of family life: the financial situation, social interaction, subjective distress experienced by the parent, and a positive sense of mastery of the situation (Financial, Familial/Social, Personal Strain, and Mastery). Each of 24 brief statements is scored from 1 ("strongly agree") to 4 ("strongly disagree"), with higher scores reflecting less perceived impact on the family. Sample items include, "The illness is causing financial problems for the family," and, "We see family and friends less because of the illness." The scale has good internal reliability, with a Cronbach’s of .88.27 Its construct validity is apparent in its correlations with medical and psychological variables in children with different health conditions.28,29 To focus on the impact on the family, rather than the family’s coping strategies, we excluded the 5 mastery items and summed the other 19 items.29
Child adaptive development was measured using the Vineland Adaptive Behavior Scales.30 For this scale, a trained examiner interviewed a parent at the child’s visit at 1-year adjusted age. The scale assesses 4 domains of adaptive development: communication, daily living skills, socialization, and motor skills. Item scores indicate whether the child performs an activity "yes, usually" (2), "sometimes or partially" (1), or "no, never" (0). The overall Adaptive Behavior Composite (ABC) is a standard score based on the child’s age, with higher scores representing better adaptive functioning. Interrater, test-retest, and split-half reliabilities range from 0.62 to 0.99.30
The Bayley Scales of Infant Development31 were used to assess child cognitive and motor development, reported as Mental Developmental Index (MDI) and Psychomotor Developmental Index (PDI), respectively. Both the MDI and the PDI are standard scores, with higher scores reflecting higher cognitive and motor skills. In this study, we report ABC, MDI, and PDI scores for the child’s adjusted age (adjusted for prematurity). The Bayley Scales were standardized on a sample of 1700 children. Internal consistency reliability coefficients range from 0.78 to 0.93 for the Mental Scale and from 0.79 to 0.91 for the Motor Scale. Repeated measures reliability (after 1–16 days) ranged from 0.87 for the Mental Scale to 0.78 for the Motor Scale. Acceptable convergent and divergent validity of the Bayley Scales was determined in a study of at-risk children.31
For this study, we regarded infants as having objective indicators of medical vulnerability when they had 1 or more of the following at 1-year adjusted age: weight/length <5th percentile, tube feeding, home oxygen, tracheostomy, cerebral palsy, severe visual impairment (involvement with a school for the blind), severe hearing impairment (use of hearing aids), ventriculoperitoneal shunt, or anticonvulsant use.
Statistical Analysis
Descriptive statistics were calculated on all measures to determine the characteristics of the sample, check normality assumptions, and ensure adequate variability. Univariate analyses were performed using t tests for dichotomous variables, analyses of variance for polychotomous variables, and linear regression analyses for continuous variables.
Linear regression analysis was used to assess the relationship between VCS score and all of the demographic, neonatal illness severity, and maternal psychosocial variables, known at neonatal discharge, that were significant at the univariate level. Variables were entered simultaneously into the model. Linear regression analyses were used to determine the relationships between VCS score and child development outcome variables, first independently and then while controlling for the presence of 1 or more objective indicators of medical vulnerability (listed above). All analyses were performed using SAS for Windows, version 8.
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RESULTS |
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Descriptive Statistics
Maternal and child demographic characteristics of the sample, indicators of neonatal illness severity, and indicators of medical vulnerability are shown in Tables 1, 2, and 3, respectively. In the entire sample of 116 mothers of premature infants with chronic lung disease, the mean score on the VCS was 48.6, with a standard deviation of 6.9, median score of 48.0, and range of 29 to 64. Children with at least 1 objective indicator of medical vulnerability at 1-year adjusted age were perceived by their mothers as being more vulnerable (lower mean VCS score) than were children with no indicators of medical vulnerability (46.5 ± 5.7 vs 49.6 ± 7.2, respectively; P < .02).
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Association Between PPCV and Child Developmental Outcome
For the entire sample, mean scores (ranges) for the MDI, PDI, and ABC were 88 (50–137), 81 (50–139), and 100 (66–122), respectively. In univariate analyses, higher perceived vulnerability (lower VCS score) was significantly correlated with lower scores for adaptive development (Vineland ABC; P = .002) and motor development (Bayley PDI; P = .02) but not mental development (Bayley MDI; P = .08). After adjusting for the presence of 1 or more indicators of medical vulnerability, higher PPCV remained significantly correlated with lower adaptive development (P = .03) but not with mental or motor development.
Children with 1 or more indicators of medical vulnerability at 1-year adjusted age had lower adaptive development (mean Vineland ABC score) than did children with no indicators of medical vulnerability (96 ± 12.4 vs 102 ± 8.5, respectively; P = .009). Because medical conditions, such as cerebral palsy, visual impairment, and growth delay, may worsen adaptive development, we performed a subset analysis in which we eliminated the children who had 1 or more indicators of medical vulnerability. In the remaining 78 children, who had no objective indicators of medical vulnerability at 1-year adjusted age, higher perceived vulnerability (lower VCS score) was strongly correlated with worse adaptive development (lower Vineland ABC score; r = .31; P = .006).
Predictors of PPCV
Relationships between PPCV at 1-year adjusted age and demographic, neonatal illness severity, and maternal psychosocial factors known at neonatal discharge are summarized in Tables 1, 2, and 4, respectively. In univariate analyses, higher PPCV (lower VCS score) was associated with nonfirstborn status; longer neonatal hospitalization; higher maternal anxiety and depression; greater impact of the illness on the family; and lower maternal optimism, life satisfaction, and social support. PPCV was not associated with any of the other demographic factors (maternal age, education, marital status, income, or ethnicity or child gender) or neonatal illness severity factors (gestational age, birth weight, or length of mechanical ventilation).
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A linear regression analysis was used to assess the relationship between PPCV and all of the variables that were significant at the univariate level (firstborn status; length of hospitalization; and maternal anxiety, depression, optimism, life satisfaction, social support, and perceived impact of the illness on the family). The regression model containing these variables explained 29% of the variance in PPCV (P = .0003). Maternal anxiety was the only variable that was statistically significant in the full model (P = .009).
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DISCUSSION |
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This study suggests that higher maternal perception of child vulnerability is correlated with worse developmental outcome in premature infants with chronic lung disease at 1-year adjusted age. In univariate analyses, higher PPCV was associated with lower adaptive and motor functioning but not with lower cognitive functioning. After controlling for medical vulnerability, the negative association between PPCV and adaptive functioning remained significant, consistent with previous research showing that parents who perceive their children as more vulnerable also tend to perceive them as developing more slowly.18 The anxiety caused by the threatened loss of a child may permanently change the way a parent perceives and interacts with a child.6 Parents may tend to shelter children whom they see as vulnerable, providing fewer opportunities for them to gain independence in activities of daily living. In this study, the negative association between PPCV and motor development can be reasonably attributed to greater severity of medical illness among children with higher PPCV. Child adaptive development, measured by parent report, is inherently more strongly influenced by parental perceptions than is cognitive development, measured objectively. This may explain why we found no significant association between PPCV and cognitive development. In a study of premature infants at 3 years of age, Estroff et al1 also found no relationship between PPCV and an objective measure of cognitive development, although mothers who saw their children as vulnerable identified them as less developmentally competent.
Our study also suggests that maternal anxiety and other factors identifiable at neonatal discharge predict maternal perception of child vulnerability at 1-year adjusted age. Mothers who saw their children as vulnerable had more anxiety and depression; less optimism, life satisfaction, and social support; and a greater perceived impact of the illness on the family. Children who were not firstborn and who had longer neonatal hospitalizations were seen as more vulnerable.
Maternal anxiety at neonatal discharge was the strongest predictor of PPCV at 1-year adjusted age in our study. Mothers of very low birth weight infants with chronic lung disease have been shown to report more anxiety than mothers of term infants.32 Mothers of premature infants are also more likely to be anxious about leaving their child with a babysitter.13 Our study extends these findings by showing that maternal anxiety is associated with increased PPCV in mothers of premature infants. Mothers who are more anxious may be more likely to perceive their premature infants as medically vulnerable.
We found that higher PPCV is associated not only with higher maternal anxiety but also with higher maternal depression and lower maternal life satisfaction, consistent with reported associations between higher PPCV and both postpartum depression16 and lower maternal well-being.3 Higher PPCV may also explain a previous observation that mothers of premature infants with low social support leave their infants less frequently and for shorter periods.33
Higher PPCV was associated also with greater impact of the illness on the family. Mothers of very low birth weight infants with chronic lung disease report greater impact on the family, even at 3 years, than mothers of term infants.32 Greater impact on the family has also been shown to be associated with lower adaptive functioning,34 poorer perceived health, and increased health care utilization35 in very low birth weight infants. Mothers who are experiencing a greater impact of the illness on their family may see their infants as more vulnerable and, in turn, seek more medical services for infants whom they perceive as having poorer health and development.
Higher PPCV among premature infants at 1-year adjusted age was associated with longer neonatal hospitalization but not with gestational age, birth weight, or length of mechanical ventilation. This suggests that length of neonatal hospitalization, which was closely correlated with gestational age, birth weight, and length of mechanical ventilation in our study, is probably much more salient to parents than other indicators of neonatal illness severity, which it summarizes. The association between higher PPCV and longer neonatal hospitalization is a new finding, which is consistent with a previous report of higher PPCV in sick, premature infants than in healthy, term infants.3 Like Estroff et al,1 we found that PPCV was not associated with birth weight or gestational age. We attribute this, at least in part, to the relatively narrow range of birth weight and gestational age in our sample. It is possible that the homogeneity of our sample of very low gestational age premature infants with chronic lung disease obscured the negative association between PPCV and birth weight previously reported by others.3,12,16
Contrary to our expectation, we found that premature infants who were not firstborn were perceived as more vulnerable than firstborn children. It is possible that mothers with healthy children at home may see their premature infant’s illness as more threatening than do mothers with less basis for comparison. Other studies of PPCV in premature infants have found either that firstborn children were perceived as more vulnerable than nonfirstborn children12 or that birth order was not associated with PPCV.1
We found no association between PPCV and other demographic variables (maternal age, marital status, ethnicity, and education; family income; and child gender). Previous studies analyzing the relationship between PPCV and demographic factors have yielded conflicting results. A study of PPCV in premature infants documented no association between PPCV and maternal age, race, or socioeconomic status.1 Studies conducted in pediatric office settings have found that higher PPCV is associated with younger parental age,9,11 unmarried marital status,9,16,36 and lower family income.9,16 Previous research has shown a negative association,16,36 no association,9 or a positive association3,12 between PPCV and maternal education. In our study, the severity of the child’s illness and the maternal psychosocial response to the illness eclipsed any minor differences in PPCV attributable to demographic factors.
As expected, children who had objective evidence of medical vulnerability at 1-year adjusted age (weight/length <5th percentile, tube feeding, home oxygen, tracheostomy, cerebral palsy, severe visual impairment, severe hearing impairment, ventriculoperitoneal shunt, and/or anticonvulsant use) were perceived by their parents as being more vulnerable than children who had none of these indicators. Clearly, objective evidence of continued medical vulnerability contributes to higher parental perception of child vulnerability in premature infants at 1-year adjusted age. The mean VCS scores of both our medically vulnerable and medically healthy premature infants (46.5 and 49.6) were lower than those of the 3-year-old formerly sick premature and healthy term infants (52.1 and 55.5, respectively) described by Perrin et al.3 The fact that the premature infants with chronic lung disease in our study were perceived by their mothers as more vulnerable at 1-year adjusted age than Perrin’s formerly sick premature infants at 3 years of age suggests that PPCV may decrease over time as children’s health improves and their parents become more confident in caring for them.
Several limitations of this study should be noted. First, all of our subjects were very low gestational age infants with chronic lung disease, limiting the extent to which our findings can be generalized to other groups of infants. Second, we did not include a control group of either term or healthier premature infants, so no inferences can be drawn about the association between prematurity and PPCV. Third, the relative homogeneity of our sample with regard to severity of illness may have masked relationships between PPCV and other variables. Fourth, we assessed developmental outcome at a relatively early age. Despite these limitations, our study should be of interest to professionals who care for families of chronically ill premature infants. Future research should involve longer follow-up of a larger, more diverse sample of infants and include a comparison group of healthier premature infants and/or term infants.
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This study suggests that higher parental perception of child vulnerability is correlated with worse developmental outcome in premature infants at 1-year adjusted age. Maternal anxiety at neonatal discharge predicts subsequent high PPCV. These findings have implications for the care of sick premature infants, who are already at increased risk for adverse developmental outcome and high health care utilization. The portion of that risk that is attributable to PPCV can potentially be modified in the first year of life. Interventions to prevent or reduce PPCV should be targeted toward more anxious parents, who can be identified using a brief, self-administered measure of anxiety. By decreasing anxious parents’ perception of child vulnerability, these interventions may prevent unnecessary health care utilization and improve developmental outcome in premature infants.
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"Once a population has a large number of people who are immune, the key question becomes: If the microbe finds a susceptible person in the mixed population, how many additional people is that victim likely to infect? ... That number is called the ‘effective reproductive number.’ When it is <1, an outbreak will disappear spontaneously because the victims in each round of infection will not ‘replace’ themselves with new victims. However, if the number is >1, the outbreak will sustain itself or grow. ... In England’s recent measles outbreaks, the ‘effective reproductive number’ has been rising—a very ominous sign. ... In the outbreaks from 1955 to 1998, the number was 0.47. For those from 1999 to 2002, it was 0.82. ... If it reaches 1, measles will be able to find enough new victims to keep the infection moving through the population—at least until something is done to raise the percentage of people who are immune. Herd immunity will be gone."
Jansen YAA. Washington Post Weekly. September 29–October 5, 2003
Submitted by Student
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ACKNOWLEDGMENTS |
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This study was supported by grant R01 HS07928 from the Agency for Healthcare Research and Quality.
We thank Debbie Hiatt and Dr Robert Dillard for clinical care of the children and families described here and Drs Kurt Klinepeter and Virginia Nichols, who helped us to develop the list of indicators of medical vulnerability.
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FOOTNOTES |
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Received for publication Sep 16, 2002; Accepted Jun 4, 2003.
Reprint requests to (E.C.A.) Wake Forest University School of Medicine, Department of Pediatrics, 3325 Silas Creek Pkwy, Winston-Salem, NC 27103. E-mail: eallen{at}wfubmc.edu
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