PEDIATRICS Vol. 122 No. 1 July 2008, pp. e100-e106 (doi:10.1542/peds.2007-1314)
ARTICLE |
Associations Between Maternal Age and Infant Health Outcomes Among Medicaid-Insured Infants in South Carolina: Mediating Effects of Socioeconomic Factors
a Division of Pediatric Epidemiology and Health Systems Research, Department of Pediatrics, Medical University of South Carolina, Charleston, South Carolina
b Departments of Epidemiology and Biostatistics
c Health Services Policy and Management, Arnold School of Public Health, University of South Carolina, Columbia, South Carolina
| ABSTRACT |
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OBJECTIVE. The objective of this study was to investigate whether infants who are born to adolescent mothers are at greater risk for health problems than those who are born to older mothers.
METHODS. Data represent all health care encounters for infants who were born in South Carolina between 2000 and 2002 and were healthy at birth and continuously enrolled in fee-for-service Medicaid (n = 41696). We separately examined in the first and second years of life use of preventive care doctor visits, sick-infant doctor visits, emergency department visits, hospital admissions, and both emergency department visits and hospitalizations for ambulatory care–sensitive conditions. We compared these outcomes for infants of adolescent mothers (aged 11–17 years) and older mothers (aged 18–47 years), adjusting for individual characteristics of mothers and infants.
RESULTS. In unadjusted results, infants of adolescent mothers used more health care in 9 of 12 use categories. For example, in year 1, they had an average of 1.71 emergency department visits and 1.39 hospitalizations, compared with 1.26 and 1.18, respectively, for infants of older mothers. In results that were adjusted only for infant and delivery characteristics, they similarly used more services in most categories. After adjustment for either mothers' characteristics alone or those of both the infant/delivery and mothers, there was evidence that they had modestly more sick-infant doctor visits and hospital admissions in year 1 and notably more hospital admissions for ambulatory care–sensitive conditions.
CONCLUSIONS. Infants of adolescent mothers are more likely than infants of older mothers to use a variety of health care services that suggest poorer health. A considerable proportion of this greater use seems to be attributable to specific characteristics of mothers, such as socioeconomic characteristics, rather than to an inability that is common among adolescents to promote infant health or to use health care appropriately.
Key Words: Medicaid adolescent mothers infant health care socioeconomic status ambulatory care sensitive conditions
Abbreviations: ED—emergency department FFS—fee for service ACSC—ambulatory care–sensitive condition FPL—federal poverty level EPSDT—Early and Periodic Screening, Diagnosis, and Treatment AAP—American Academy of Pediatrics RR—rate ratio CI—confidence interval
Adolescent pregnancy is a public health concern with striking psychological, social, and physiologic ramifications for young women and their infants.1,2 Numerous studies have described poor reproductive outcomes for adolescent pregnancy, attributing adverse events to a variety of causes, including lifestyle, ethnic and cultural background, socioeconomic status, marital status, education, place of residence, and inadequate accessibility and use of health care.3–8 Some researchers suggested that socioeconomic status is a primary determinant of adverse outcomes for adolescent pregnancies.9,10
Health status and health care use of infants of adolescent mothers has been less well described than their mothers' reproductive outcomes. Studies of this issue, which are primarily descriptive, have mixed results. Some indicated more intentional and unintentional injury and hospitalization for infants of adolescents and a lack of immunization.11–13 Others described no differences in emergency department (ED) visits, hospitalizations, or immunizations for infants of younger and older mothers.14–16
Limited available research suggested that the average adolescent mother has lower income than the average older mother, less education, and less awareness of her infant's medical needs, suggesting less ability to promote infant health.2,8,17–19 The association between infant health and socioeconomic status limits the usefulness of most studies of this issue, which typically rely on health care claims data that do not permit individual-level controls for characteristics such as education or income.20 Results of studies without individual-level controls for socioeconomic characteristics provide uncertain evidence about risks for infant health that may actually be attributable to characteristics of young mothers, such as an ability to promote infant health by using health care appropriately. Thus, well-controlled empirical investigation of health care use by infants of adolescent mothers is needed by physicians and policymakers for appropriate design of interventions to improve health status and to coordinate health service use. If poor infant outcomes are an independent function of adolescent mothering, then efficient interventions might differ from those that would be appropriate if other factors account for these outcomes, such as mothers' socioeconomic characteristics or serious conditions that affect infants at birth.
We used unique data from South Carolina to examine whether there were differences in infant health outcomes associated with maternal age, controlling for individual-level socioeconomic characteristics of mothers and several infant characteristics. We hypothesized that, among term, appropriately grown infants who are insured by fee-for-service (FFS) Medicaid in South Carolina, those of adolescents and those of older mothers would have similar health care use, generally indicating similar health status, in their first 24 months of life, when socioeconomic characteristics are controlled. Specifically, we hypothesized that infants of adolescent and older mothers use similar numbers of preventive-care doctor visits, sick-infant doctor visits, ED visits, hospitalizations, and both ED visits and hospitalizations for ambulatory care–sensitive conditions (ACSCs).
| METHODS |
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Population Studied
A total of 61112 births were insured by Medicaid in South Carolina in 2000, 2001, and 2002. Among these, 59216 (96.9%) were enrolled in FFS Medicaid at some time during the first 2 years of life. Infants are often not enrolled in their Medicaid insurance plan until sometime during the first month of life. Thus, we studied infants who were continuously enrolled in FFS Medicaid from the second through the 24th months of life and calculated the number of visits or stays for the first year on the basis of the second through 12th months of life. The requirement that infants must have been continuously enrolled in FFS excluded 1215 infants who switched from FFS to Medicaid managed care in the first 24 months. Another 25 infants whose insurance switched from Medicaid managed care to FFS were also excluded from the analysis. The term "adolescent mother" is defined for this investigation as a mother who was younger than 18 years at the time of delivery. The threshold distinguishing adolescent and older mothers, age 18, was selected for consistency with previous studies.19,21 This age is consistent with high school graduation, voting, and increased independence.
The data, obtained from the South Carolina Budget and Control Board, Office of Research and Statistics, linked state Medicaid claims and birth certificate files. All infants who are insured by South Carolina Medicaid have low income (up to 185% of the federal poverty level [FPL]); therefore, restricting the investigation of infant health to those who were insured by Medicaid provided a useful degree of control for socioeconomic status. Furthermore, the South Carolina statewide Medicaid data include detailed individual-level measures of socioeconomic characteristics of mothers, such as marital status, level of income, and education, information that is not available in administrative data. Our previous research using the South Carolina Medicaid data indicated that the data and linkages required for this research have a high degree of completeness and validity.21–24 In this study, the linkage was successful for 94% of the infants who were covered by Medicaid during the study years.
The usual expectation in research on this topic is that health outcomes are likely to be associated with mothers' abilities to maintain infant health, to identify health problems, and to seek an appropriate level of care in a timely manner when infant health care needs arise. Thus, it was desirable to exclude infants who had conditions that might predispose them to use the health care services that we examined. The study excluded infants with birth admissions that lasted
7 days or with major heart diseases or conditions (International Classification of Diseases, Ninth Revision, Clinical Modification codes 745.4, 745.5, 759.9, 747.41, 747.0, 745.1, 745.2, 746.7, 747.10, 746.87, and 745.0), central nervous system malformations (742.3, 742.1, 655.0,653.60, and 653.63), genitourinary anomalies (752.7, 752.61, 752.62, and 752.51), gastrointestinal anomalies (751.2, 530.1, 750.3, and 751.4), musculoskeletal anomalies (756.9), and recognizable genetic malformations (758.0,758.1, 758.2, 760.71, and 282.6).
Infants were also restricted to those who were term and appropriately grown at birth, by requiring at least 37 weeks' gestational age, and infant birth weight within published fetal growth norms.25,26 Infants with birth weight below the fifth percentile for infants aged 37 to 42 weeks or above the 95th percentile were excluded from the analysis. These restrictions excluded 16280 infants; the majority of exclusions were attributed to birth anomalies (n = 11552), birth weight outside fetal growth norms (n = 6878), and gestational age <37 weeks (n = 7491). Of the infants excluded, 5913 met >1 of these criteria.
These exclusions, which provided a control for baseline infant health and ensured uniform effects of insurance model, produced a final analytic sample of 41696. This study was approved by the institutional review board of the Medical University of South Carolina and the South Carolina Data Oversight Commission, which supervises use of Office of Research and Statistics data.
Dependent Variables
Dependent variables that were analyzed in separate models included the number of Early and Periodic Screening, Diagnosis, and Treatment (EPSDT; preventive care) doctor visits; sick-infant doctor visits; ED visits; hospital admissions; and both ED visits and hospital admissions specifically for ACSCs. The specific diagnoses for ACSC ED visits and hospitalizations, identified using International Classification of Diseases, Ninth Revision, Clinical Modification codes, are those previously reported to be the most common ACSC diagnoses in ED and hospital settings for infants who are insured by Medicaid27: asthma; seizure; cellulites; ear, nose, and throat infections; bacterial pneumonia; kidney/urinary tract infection; and gastrointestinal infections.
The EPSDT benefit, added to Medicaid in 1967, was designed to prevent disease in children and to detect and treat health problems before they become more serious.28–30 The American Academy of Pediatrics (AAP) recommends 6 EPSDT visits in the first year of life and 3 in the second year.31,32 These recommendations have been endorsed by the South Carolina Department of Health and Human Services for infants who are enrolled in Medicaid. The number of infant EPSDT visits represents the combined number of visits for immunizations and/or screening services. EPSDT visits were identified using the Health Care Financing Administration Common Procedure Coding System codes and definitions published in the Physician's Current Procedural Terminology.33 We also examined, for each year of the analysis, whether the infant received the AAP-recommended number of EPSDT visits.
Exposure Variable
The exposure variable, or independent variable of primary interest, was maternal age at delivery. For statistical comparisons, this analysis dichotomizes infants into 2 groups: those whose mother was 11 to 17 years of age at the time of delivery and those whose mother was 18 to 47 years of age.
Control Variables
Control variables included a number of characteristics of mothers, such as education in years. Dummy variables indicated whether the mother was married; whether the mother was non-Hispanic white, black, Hispanic, another race or ethnicity, or had a missing value for race/ethnicity; family income
50% of the FPL or greater (up to 185% of the FPL); maternal parity; whether the delivery was vaginal; whether the mother smoked, drank alcohol, or used illicit drugs during pregnancy; and whether the mother received adequate prenatal care, as defined by the Kessner Index of Prenatal Care Adequacy.34,35 Information about maternal use of alcohol, tobacco, and illicit drugs during pregnancy was obtained by health care providers by asking the mothers about use during their postpartum hospitalization and examining the mothers' responses recorded on birth certificates using specific diagnosis-related groups: alcohol use (65811), tobacco use (65651), and illicit drug use (65801). We controlled for type of delivery, vaginal or cesarean section, because it has been reported that the birth of a child in any way out of the ordinary (surgical delivery) may create parental emotional discomfort that affects infant care through the first 2 years of life or longer.36
Also included in the model were several controls for infant characteristics. Rural/urban residential status was assigned on the basis of the largest town in the infant's county of residence. Infants who resided in counties with a town of at least 25000 residents were considered to reside in urban areas; those in remaining counties were considered to reside in rural areas. Additional infant controls were birth weight in grams, gender, and gestational age in weeks. These controls were included because parenting behaviors have been associated with such factors. Although we excluded infants with low birth weight or congenital conditions, it remained useful to include in the models individual-level measures of infant development because parental behavior is clearly influenced by even minor deviations from expectation.37,38 Gestational age and birth weight were examined for nonlinear associations with the outcome variables by entering each measure into the models as a set of dummy variables. The results suggested that the associations between both measures and the outcomes were generally linear, a result that is consistent with previous research. Thus, for providing the maximum adjustment for potential confounding across all levels of these measures, both were entered into the final models as continuous variables.
Statistical Analysis
Bivariate analyses compared characteristics of mothers and infants according to mother's age group.
2 tests were conducted for categorical data, and t tests were conducted for continuous measures.
Because the count data in the analysis exhibited overdispersion, negative binomial regression was used to compare rates of health care use for adolescent and older mothers. Overdispersion occurs when the variance of the dependent variable notably exceeds its mean. This data characteristic can seriously challenge the analysis of count data. When present, this phenomenon can produce underestimates of SEs, leading to faulty conclusions about statistical significance. Negative binomial regression corrects the SEs.39 Multivariate analyses assessed effects of maternal age at delivery on each dependent variable, adjusted for relevant characteristics of the mothers and infants. Multicollinearity was assessed for each regression model; multicollinearity was not a problem for any of the analyses. Stata statistical software (Stata Corp, College Station, TX) was used for all analyses.
| RESULTS |
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Table 1 shows the bivariate comparisons of maternal and infant characteristics, stratified by maternal age at delivery. Adolescent mothers averaged age 16.2 years, compared with 24.3 years for the older mothers. Adolescent mothers were less likely to be married (6.8% vs 20.2%), were more likely to be primiparous (91.0% vs 35.2%), and, as expected for adolescents, had lower educational attainment (9.8 vs 11.8 years; all P < .0001). Other differences between adolescent and older mothers were in most instances minor, although adolescents were less likely than older mothers to have an adequate rating on the Kessner Index of Prenatal Care Utilization (52.5% vs 64.3%; P < .0001).
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Table 2 shows the mean number of times each type of service was used by infants of adolescent and older mothers. Table 2 also shows the unadjusted ratios of these means (rate ratios [RRs]) and their confidence intervals (CIs), where the rate for infants of adolescent mothers is the numerator. An RR > 1.00 indicates that infants of adolescent mothers used more of the service than infants of older mothers. For example, in year 1, infants of adolescents had an average of 1.71 ED visits, compared with 1.26 for infants of older mothers. Thus, the rate of ED visits in year 1 was 36% greater for infants of adolescent mothers than for infants of older mothers (RR: 1.36 [95% CI: 1.30–1.41]). In these unadjusted results, infants of adolescent mothers used more health care in 9 of 12 service categories. Moreover, these differences seemed to be clinically significant in all but 2 of the comparisons: EPSDT visits in years 1 and 2. There were no significant differences between maternal age groups in the percentage of infants who received the AAP-recommended number of EPSDT visits in either year 1 or 2 (data not shown).
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Table 3 presents results adjusted for socioeconomic factors and delivery characteristics shown in Table 1. Model 1 shows the results adjusted for infant and delivery characteristics only. Model 2 reports results adjusted only for maternal characteristics. Model 3 shows results adjusted for both infant/delivery characteristics and maternal characteristics. For each model and outcome, Table 3 presents the adjusted RR associated with the covariate indicating whether the mother was an adolescent or an adult and the corresponding CI. An RR of >1.00 suggested that infants of adolescent mothers had greater adjusted use of the given outcome. In model 1, the results suggested that infants of adolescent mothers were more likely to use services in 11 of the 12 categories, controlling for infant and delivery characteristics. The RRs suggesting this greater use were particularly notable for ED visits in both years 1 and 2 (respectively, RR: 1.34 [95% CI: 1.29–1.40] and RR: 1.32 [95% CI: 1.26–1.37]), hospital admissions in year 1 (RR: 1.17 [95% CI: 1.10–1.25]), ACSC ED visits in both years 1 and 2 (respectively, RR: 1.33 [95% CI: 1.27–1.40] and RR: 1.33 [95% CI: 1.26–1.40]), and ACSC hospitalizations in both years 1 and 2 (respectively, RR: 1.19 [95% CI: 1.02–1.39] and RR: 1.24 [95% CI: 1.05–1.47]), with additional evidence of modestly greater use of sick-infant doctor visits in year 1 (RR: 1.06 [95% CI: 1.00–1.12]). When only mothers' characteristics were controlled (model 2), there was again evidence of modestly greater use of sick-infant doctor visits in year 1 for infants of adolescents (RR: 1.07 [95% CI: 1.00–1.06]) and of notably more hospital admissions in year 1 (RR: 1.27 [95% CI: 1.03–1.57]). Adjusted for both infant/delivery and mothers' characteristics (model 3), results again suggested modestly greater use of sick-infant doctor visits in year 1 for infants of adolescents (RR: 1.08 [95% CI: 1.00–1.17]) and also more hospital admissions in year 1 (RR: 1.09 [95% CI: 1.01–1.18]), as well as notably higher rates of hospitalization for ACSCs in year 1 (RR: 1.29 [95% CI: 1.04–1.60]).
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| DISCUSSION |
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This study compared health care use by infants of adolescent mothers with that by infants of older mothers. Consistent with previous research, our expectation is that use of these services is an indicator both of infant health and of mothers' ability to promote infant health and use health care appropriately. Unadjusted results suggested a number of differences in health care use between infants of younger and older mothers. Most of these differences persisted after adjustment for characteristics of infants and deliveries; however, most of these differences did not persist after adjustments either for maternal characteristics only or for both infant/delivery and maternal characteristics. Holding all else constant, for both years 1 and 2, there were no differences in EPSDT visits, ED visits, or ED visits for ACSCs. Moreover, again holding all else constant, there were no differences in year 2 in the number of sick-infant doctor visits, the number of hospital admissions, and the number of hospitalizations for ACSCs. There was modestly greater use by infants of adolescents of sick-infant doctor visits and hospital admissions in year 1. The only large significant adjusted difference among the outcome variables was for hospitalization for ACSCs in year 1, for which infants of adolescent mothers were at higher risk. Considered together, these findings are consistent with our hypothesis, suggesting similar health status and patterns of health care use for infants of adolescent and older mothers, particularly after adjusting for individual-level characteristics of mothers. Furthermore, the proportion of infants who received the AAP-recommended number of EPSDT visits in both years 1 and 2 was the same for infants of adolescent and older mothers, and the adjusted results also suggested no difference between these groups for EPSDT visits. These findings support the hypothesis that adolescent mothers generally provide for needed infant care as well as older mothers who otherwise share similar characteristics.
Several factors should be considered when evaluating these results. The analysis required a successful linkage of health care use data from Medicaid and birth certificates. This linkage could not be made for 6% of the infants covered by Medicaid during the study years. There were no meaningful differences in the characteristics of infants whose data could be linked and those whose data could not.
Most infants who were insured by Medicaid during the study years were enrolled in FFS. They were automatically enrolled in FFS unless the parent or guardian elected to enroll in managed care. In other states, infants who are covered by Medicaid are much more commonly enrolled in managed care. In previous research, we extensively analyzed the characteristics of infants who were insured by FFS and managed care in the South Carolina Medicaid system, finding few systematic differences between those in FFS and the state's 2 managed care programs,23 although those in FFS were less likely to have adequate prenatal care than those in managed care. Results of this study may not be generalizable to infants who are insured by Medicaid managed care.
It was desirable to control for infants' conditions that might especially predispose them to use the health care services that we examined. Thus, infants with congenital conditions or low birth weight and/or preterm infants were excluded from the analysis, and control subjects were included in the models for other characteristics of infants and their deliveries. Inferences from the results should not be extended to infants in the excluded categories. Also controlled were characteristics of the mothers that may confound the relationship between maternal age and infant outcomes, such as education, income, and marital status. Unmeasured selection factors may nonetheless bias the results.
Furthermore, our controls for maternal use of alcohol, tobacco, or illicit drugs during pregnancy relied on birth certificate data, which originate from mothers' self-reports. Available studies suggested that women self-report smoking during pregnancy with reasonable accuracy.40,41 There is no accepted biological marker for diagnosing long-term ethanol exposure in utero,42 although studies that used available biological markers for ethanol exposure, such as fatty acid ethyl esters, suggested little correlation between maternal self-reporting of ethanol use during pregnancy and the presence of this marker.41 Thus, although available data provide mixed results, relying on maternal self-reports of substance use during pregnancy may introduce bias associated with measurement error.
It should be noted that the large number of comparisons shown in Table 1 may have given rise to type 1 error for some comparisons, particularly those for which the associated P value provides more modest evidence of statistical significance (eg, rural/urban residence). We also note that the large sample studied in this analysis is likely to produce statistically significant differences, in part as a function of sample size alone. For example, illicit drug use differed between adolescent and older mothers (P < .0001); however, the difference between the rate for adolescents (2.8%) and the rate for older mothers (2.1%) may not be clinically relevant.
Research has suggested that at hospital discharge, most first-time mothers expect to be the infant's primary caregiver.17 Nonetheless, whether adolescent mothers lived with their parents or other potential caregivers may have contributed to the results, potentially influencing perceived need for clinical care and its use. To the extent that this is a characteristic limited to adolescent mothering, the results would nonetheless accurately reflect risks of adolescent mothering; however, the lack of a measure in our data for such living arrangements and their effects on care use, for both adolescent and older mothers, may have resulted in unmeasured confounding and potential bias. Also, the income measure that was available for this research provided only limited information about the level of income. It is possible that alternative measures of income might affect the results. It is also possible that there may be residual confounding associated with the sites at which either adolescents or older mothers received care or with the type of outpatient setting. These factors were not controlled in our models. Concern about this potential should be ameliorated considerably by the likelihood that such factors may be associated with the socioeconomic characteristics for which the models controlled.
The analysis controlled for individual-level measures of infant development, because parental behavior may often be influenced by even minor deviations from expectation.36–38,43–45 Researchers have speculated that this effect may cross all levels of socioeconomic status,46 although there has been little empirical study of this possibility. This effect may differ depending on the type of infant anomaly47 or on family structure or ethnicity.48 Thus, the estimates in this study may be affected by some degree of residual confounding, despite the control for infant characteristics.
| CONCLUSIONS |
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We found that infants of adolescent mothers are more likely than infants of older mothers to use a variety of health care services that suggest poorer health and that a considerable proportion of this greater use seems to be attributable to specific characteristics of mothers, such as socioeconomic characteristics, rather than to some inability of adolescents to promote infant health or to use health care appropriately. These results suggest that policies that aim to provide additional social support to adolescent mothers49 or additional financial resources may be useful ways to improve the health outcomes of infants who are born to younger women. Additional research is needed, however, to identify specific interventions that may improve health outcomes for infants of adolescents.
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Accepted Jan 2, 2008.
Address correspondence to William B. Pittard III, MD, PhD, MPH, Medical University of South Carolina, Department of Pediatrics, Division of Pediatric Epidemiology and Health Systems Research, 165 Ashley Ave, PO Box 250917, Charleston, SC 29425. E-mail: pittardw{at}musc.edu
The authors have indicated they have no financial relationships relevant to this article to disclose.
| What's Known on This Subject Health status and health care utilization of infants of adolescent mothers has been less well described than their mothers' reproductive outcomes. Studies of this issue, which are primarily descriptive, have had mixed results.
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| What This Study Adds This study provides well-controlled empirical investigation of health care use by infants of adolescent mothers needed by physicians and policy makers to appropriately design interventions to improve health status and coordinate health service use.
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PEDIATRICS (ISSN 1098-4275). ©2008 by the American Academy of Pediatrics
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