Hospitalization of very low birth weight children at shcool age

Hospitalization of very low birth weight children at school age M a r i e C. M c C o r m i c k MD, ScD, K a t h r y n W o r k m a n - D a n i e l s , PhD, J e a n n e B r o o k s - G u n n , PhD, a n d G e o r g e J. P e c k h a m , MD From the Joint Program In Neonatology, Department of Pediatrics, Harvard Medical School, and the Department of Maternal and Child Health, Harvard School of Public Health, Boston, Massachusetts, the Center for the Study of Children and Families, Teachers College, Columbia University, New York, New York, the Educational Testing Service, Princeton, New Jersey, and the Division of Neonatology, Department of Pediatrics, Children's Hospital of Philadelphia, Philadelphia, Pennsylvania

Objective: To assess whether very low birth weight (VLBW) increases the risk of hospitalization at school a g e . Design: Prospective, multisite cohort study. Participants: Selected from a previous multisite, hospital-based trial, 611 VLBW children, and, from a prior representative sample, 724 children who weighed 1501 to 2500 gm and 533 who weighed >2500 gin. All the children were recontacted at 8 to 10 years of a g e for this study. Methods: Maternal interview with the use of standardized questions. Main outcome: Hospitalization in year before interview. Results: The VLBW children were three or four times more likely to be rehospitalIzed than children of normal birth weight, both In the year before the interview (7% vs 2%) and since birth (50% to 60% vs 22%). Morbidity and M e d i c a i d covera g e increased the risk of hospitalization In the year before the Interview; nonwhite race d e c r e a s e d il. After control for other factors, however, lower birth weight remained a significant risk factor for hospitalization. Conclusions: The VLBW children continue to have an Increased risk of hospltalization; the risk is similar in magnitude to that seen In infancy. (J PEDIATR4993; 122:360-5) Very low birth weight is a well-documented risk factor for rehospitalization in infancyl-5; congenital malformations

Supported by a contract from the National Institute of Child ltealth and ttuman Development, in conjunction with the Bureau of Maternal and Child Health (NOI-IID-5-2928), and by grants from the Robert Wood Johnson Foundation (9104) and the William T. Grant Foundation (86-0401-92). The content of this publication does not necessarily reflect the views or policies of the Department of Ilealth and Iluman Services, nor does the mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government. Submitted for publication April 22, 1992; accepted Oct. 2, 1992. Reprint requests: Marie C. McCormick, MD, ScD, Professor and Chair, Department of Maternal and Child Health, ttarvard School of Public Health, 677 Iluntington Ave., Boston, MA 02115. Copyright 9 1993 by Mosby-Year Book, Inc. 0022-3476/93/51.00 + .10 9/20/43124

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and conditions associated with complications of the neonatal period account for much of the increased risk. 1"5 After the first year, the influence of these conditions has decreased,I, 5.6 suggesting that L B W children may cease to have more frequent hospitalization than normal birth Ci LBW NBW OR PDA VLBW

Confidence interval Low birth weight (--<2500 gm) Normal birth weight (>2500 gm) Odds ratio Patent ductus arteriosus Very.low birth weight (_<1500 gm)

weight peers. Tile few studies 5, 7 that have examined hospital use among older V L B W children have produced conflicting results and may not be generalizable to the United States because of its more heterogeneous populations and

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medical care system. However, the question remains an important one both for providing anticipatory guidance to the parents of individual children and for assessing the effects of neonatal intensive care more generally. 8-12 We examined whether VLBW continues to confer increased risk of hospitalization and what factors may influence the risk in a large, recent sample of children of varying birth weights. METHODS Sample. The data for this report were obtained through an assessment of children who had participated in two previous multisite studies. Details of cohort reconstruction and assessment of health status at school age have been published elsewhere. 13, 14 The VLBW children came from 10 of the 13 original centers participating in a National Heart, Lung, and Blood Institute randomized, controlled trial of indomethacin for the treatment of patent ductus arteriosus.lS, 16 All children who had been discharged alike and were not known to have died in the intervening period at the 10 sites able to participate in this study were eligible for follow-up. From this cohort we selected all children with birth weights _<1000 gm (n = 395) and a random sample of children weighing 1001 to 1500 gm (n = 656). For observations on children of similar age but of heavier birth weight, children originally assessed during infancy as part of the evaluation of the Robert Wood Johnson Foundation ( R W J F ) National Perinatal Regionalization Demonstration Program were selected from the areas of Syracuse, New York, Dallas, Texas, and Cleveland, Ohio. 17-19A sample of all infants with l-year information was selected for follow-up at school age, to include 1172 children who weighed ~ 2 5 0 0 g m a t birth (including a small number of VLBW children) and 685 children who weighed >2500 gm. All children in the study were contacted between April 1986 and November 1988 by using a prespecified approach to locating and recruiting families. 13 Overall, follow-up information was obtained on 65.1% of the entire sample. When respondents were compared with nonrespondents, the major predictor of nonresponse common in both cohorts was maternal educational attainment of less than high school graduation when the child was an infant. In both cohorts the indicators of higher levels of neonatal morbidity were associated with higher response rates (neonatal length of hospitalization greater than the 75th percentile for birth weight in the R W J F cohort, birth weight ~1000 gm in the PDA cohort). Mean ( + S D ) age at follow-up was 110.8 + 9.5 months (115.0+ 6.1 months for the R W J F cohort; 100.3 -4- 8.1 months for the PDA cohort); thus the majority of children were between 8 and 10 years of age. Data collection. Data were derived from a parent interview on intervening child health, use of health services, and sociodemographic factors. To take into account the slightly

31cCormick et al.

361

different ages of the children in the two cohorts, we selected only items that would be appropriate over the entire age range or capable of generating age-standardized measures. Hospitalization. Questions about hospitalization were derived from previously used instruments I. 20 and included questions about overnight stays in the hospital within the past year and follow-up questions about the number of episodes and the date, hospital, length of stay, reason for admission, and details of any surgery for each episode. Additional, similar questions dealt with earlier admissions. Health status. A multidimensional approach to the definition of health status was employed and described in detail. 14 Morbidity, functional impact of health status, and mental health were assessed. Morbidity was determined by the presence or absence of 17 specific conditions derived from the National Health Interview Survey. 2~ Functional impact of health status was evaluated by the presence or absence of limitations in activities of daily living because of health status and was measured by using a 16-item scale modified from that developed for the National Health Insurance Study, 21 with higher scores indicative of more activities limited by health problems. Mental health was assessed by focusing on child behavior problems, measured by using a checklist developed by Peterson and Zil122 for the National Study of Children, with higher scores indicative of more behavior problems. Characteristics o f health services used. Usual sources of health care for the child were categorized as follows: physician's office (also included group practice and private clinics), hospital outpatient clinic, public clinic (neighborhood health center or public health clinic), and other (no usual source, hospital emergency department only). Insurance coverage for the child included private (Blue Cross/ Blue Shield, other private insurance), Medicaid, self-pay (i.e., none mentioned), and other (includes Title V [Social Security Act, 1935] programs and health maintenance organizations for which the specific source of payment was not noted). Sociodemographic and neonatal factors. Sociodemographic factors that were asked about included family income at the time of the interview, maternal educational attainment when the child was an infant, and maternal age at the child's birth. Important neonatal factors included the child's race, gender, plurality, birth weight, and length of hospital stay during the neonatal period. The last was coded as either greater than, or equal to or less than, the 75th percentile for birth weight, paralleling a neonatal severity score developed by Scott et al. 23 Analysis. Comparisons by birth weight of categorical variables relied on chi-square analysis (with odds ratios where appropriate). Pairwise comparisons of differences in mean values were assessed with the Tukey Studentized

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M c C o r m i c k et al.

The Journal of Pediatrics March 1993

Table I. Sociodemographic factors and characteristics of child health care use by birth weight Birth w e i g h t ( g m ) --<1500 (n = 614)

Male 45.8 Nonwhite 38.5 Maternal age 20.0 __<19yr
1501-2500 (n = 724)

>2500 (n = 533)

53.0 30.5 21.0

49.9 17.8 10.9

28.3

i 6.3

41.0

27.4

61.6 16.3

58.7 !.1

14.1 8.8

5.8 6.2

15.6 16.8

9.8 8.8

Range Test. 24 Multivariate logistic regressions were used to assess the most significant predictors of health care use. All analyses were conducted by using Statistical Analysis Systems (SAS Institute Inc., Cary, N.C.), 25 except for crude ORs, which were obtained by using Epi Info 3.0 software. 26 RESULTS Rehospilalization. Of 611 VLBW children in the study, 6.9% had been rehospitalized in the year before the interview, compared with 1.8% of the 533 NBW children (OR = 2.98; CI = 2.00 to 4.45). The risk among heavier LBW children compared with NBW children was intermediate; 5.0% of 724 children with birth weights between 1501 and 2500 gm were hospitalized (OR = 2.74; CI = 1.29 to 5.94). The risk of hospitalization among the 247 children with birth weights ~1000 gm did not differ significantly from that among other VLBW children (6.5% vs 7.2%). Cumulatively, 54.7% of the VLBW children had ever been hospitalized, compared with 34.5% of the heavier LBW children and 22% of NBW children. Among those hospitalized in the year before the interview, the average (___SD) number of days of hospitalization was 5.2 + 7.0. The difference in the number of average hospital days was not significant in VLBW and heavier birth weight children. When the reasons for hospitalization in the year before the interview were examined, respiratory illness predominated, with asthma the single most frequent diagnosis (13 of 99 hospital episodes among the 88 children hospitalized). Other lower respiratory tract conditions (pneumonia, bron-

chitis) accounted for another eight admissions. A third of the episodes were related to upper airway problems, primarily recurrent ear infections and tonsillitis, and related surgical interventions such as myringotomy tube placement, and tonsillectomy with adenoidectomy. No difference by birth weight was seen for the proportion of episodes caused by either upper or lower respiratory tract conditions. The VLBW children with and without a history of bronchopulmonary dysplasia did not differ in the risk of hospitalization in the year before the interview (6.2% vs 7.1%; chi-square value = 0.035; p = 0.85). Of all episodes, 11 related to central nervous system disorders, including seizures, cerebral palsy, veritriculoperitoneal shunt revisions, and meningitis; all these hospitalizations were of LBW children, including 9 of the I 1 hospitalizations of VLBW children. Another eight hospitalizations were accounted for by abdominal problems, such as pain, hernias, and appendicitis. A further eight episodes were for injuries of various types, and these occurred almost entirely among the non-VLBW children. The remaining episodes covered a wide range of individual diagnoses. To assess whether lower birth weight increased the risk of hospitalization independent of factors associated with both birth weight and health care of children,27' 28 we first examined which factors differed among the birth weight groups. Increased morbidity in terms of the presence of one or more of the 17 conditions, limitation of one or more activities of daily living by health problems, and clinically significant behavior problem scores has been reported. 14 The VLBW children also differed from heavier birth weight children in sociodemographic factors and characteristics of medical care use (Table I). Because the VLBW children were more disadvantaged, they relied on Medicaid and on hospital or public health clinics for care. By definition, one fourth of each birth weight grou p had had a longer-thanaverage neonatal hospital stay. When these factors were entered into a logistic equation (Table II), nonwhite race entered the equation, as did Medicaid coverage, higher birth order, and measures of morbidity. Even after control for morbidity, however, lower birth weight continued to be a highly significant predictor of hospitalization. DISCUSSION We conclude that VLBW children continue to have an increased risk of rehospitalization at school age. The magnitude of this risk is similar to that in infancy, although for all birth weight groups the rates of hospitalization are lower in childhood than in infancy. I, 5, 6 The reasons for this increased risk are not totally clear. Respiratory conditions account for half the admissions in all birth weight groups. Thus some proportion of the increased risk of hospitalization could be due to increased respiratory

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illness or to greater severity of such illnesses. The VLBW infants have greater vulnerability to lower respiratory tract infections,29, 30 and early respiratory infections increase the risk of respiratory symptoms later in childhood.31, 32 Alternatively, persistent respiratory symptoms may reflect altered pulmonary function because of neonatal respiratory distress. 33"35 Finally, environmental factors that affect the risk of asthma or hospitalization for asthma, wheezing, or both may occur disproportionately among VLBW children.36. 37 Although VLBW children are more likely to be hospitalized for central nervous system conditions (e.g., shunt revision, cerebral palsy), this disadvantage is somewhat offset by a reduced risk of hospitalization for other reasons such as injury. Moreover, although VLBW children are at increased risk for a variety of health problems, such considerations do not explain the persistent, independent contribution of lower birth weight to the risk of hospitalization after control for this morbidity and other factors. Underascertainment of morbidity may have occurred, although interview approaches represent the most widely used technique for obtaining such information. An alternative is that birth weight reflects a persistent sense of vulnerabilityconcerning VLBW children on the part of parents, providers; or both, irrespective of the child's subsequent health status, 3s'4~ but our analyses do not provide support for the influence of past health events in maternal assessment of current health. 41 Besides birth weight and morbidity, few of the other variables used in this analysis were associated with an increased risk of hospitalization. Our results are similar to those for infancy; lower socioeconomic status, usual source of medical care, and insurance coverage t, 42 are associated with the rate of health care use. Adjusting for other factors in the equation, a nonwhite child is substantially less likely to be admitted to the hospital than a white child. These results are consistent with other work documenting access problems for nonwhite persons generally43 and for children needing ambulatory care, 44 and argue for renewed attention to access to and use of health care for vulnerable groups such as VLBW children. Interpretation of the results should include consideration of the limitations of the study. The first limitation is the rate of completion of the study. Our previous analyses for the heavier birth weight children 13 revealed that less maternal education and longer hospitalizations in the newborn period were significant predictors of noncompletion.The results for the VLBW group are similar. The pattern of nonresponse may affect estimates of rehospitalization rates but in ways that are difficult to predict. Other analyses,45 however, suggest that selection biases resulting from cohort attrition are less likely to influenceanalyses of factors associated with the use of health services.

M c C o r m i c k et al.

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II. Multiple logistic regressions of factors associated with hospitalization in year before Interview Table

Hospitalization in year before Interview Variable

Male gender Nonwhite race Maternal education 75th percentile for BW Hospital clinic usual source of care Public health clinic for care Medicaid coverage Self-pay 1+ Specified conditions 1+ Limits in ADL Behavior problem scale >14 BW (gm) 1000 1 0 0 1 - 1500 1501-2500

Adjusted OR

Cl

1.34 0.51 0.97

0.84-2.16 0.27-0.95" 0.52-1.83

0.89

0.45-1.79

0.56 1.28

0.31-0.99" 0.72-2.27

1.16 1.39

0.62-2.17 0.78-2.47

1.58

0.78-3.21

0.56

0.22-1.39

2.18 0.72 2.34 i.76 0.87

1.08-4.39* 0.28-1.84 1.30-4.22" 1.07-2.91" 0.51-1.47

3.30 3.47 2.75

1.35-8.09* 1.46-8.25* 1.25-6.03*

HSG, High schoolgraduation;BIV, birth weight;ADL, activitiesof daily

living. *p <0.05 "]'Maternaleducationalattainmentof lessthanhighschoolgraduationwhen child was an infant. Another limitation stems from the heavy reliance on maternal reports, but unfortunately our resources were insufficient to attempt a validation of these reports. To reduce biases in reporting, we restricted questions about hospitalization to a time (1 year) during which recall is dependable46; the questions were derived from previous questionnaires used in national samples.2~ Furthermore, confidence in our results is derived from the comparability of findings with other studies of rehospitalization in VLBW children.5,6 However, provider-based analyses would be desirable to complement studies based on maternal reports. The study is also constrained by geography and time and by our dependence on the two previotisly conducted studies. A major limitation stemming from the location of the study sites is the relatively few Hispanic children assessed. Moreover, the study reflects the intensive care experience almost 10 years ago. With increasing survival rates for very tiny infants, the available data suggest that morbidity has not

364

M c C o r m i c k et al.

varied as m a r k e d l y a s survival. II However, t e m p o r a l c h a n g e s in morbidity and other factors m a y influence projections from our data to current survivors. Reliance on reconstructing two previously studied groups of infants, although an economic way of obtaining prospective data, incurs the constraints of the previous studies. For example, the fact t h a t the V L B W children constitute a hospital-based sample m a y create a bias toward sieker infants, but the elimination of those with major m a l f o r m a t i o n s would have the opposite effect. Finally, the relatively small sample of events m a y limit our power to detect differences by birth weight across the broad range of potential diagnoses for which children might be hospitalized. Despite these limitations our results indicate that, although health care use diminishes for all children by early school age, the risk of increased hospitalization in V L B W children relative to N B W children remains similar to that in infancy. A portion of this risk m a y reflect the persistence of conditions related to the complications of prematurity. Even after control for morbidity, V L B W exerts a substantial independent risk of hospitalization even at school age, a finding that requires further research with the aim of reducing morbidity a m o n g these children. We acknowledge the contributions of Drs. Judy Bernbaum, Sarah Friedman, Michael Guilfoyle, Ruby P. Hearn, Marsha Iloffman-Williamson, Woodie Kessel, Donald McNellis, Alex Nadas, Marcia Sass, Peter Vietze, Susan Weller, and Sumner Yaffe; Professor Sam Shapiro; and Judith Baker to this project. In addition, we are grateful for the technical assistance provided by Patrick DiGiacomo, Ann Payson, Lorraine Luciano, JoAnna Tuner, and Alice Morris, and the staff at participating sites.

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9.

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