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Do Protective Factors Reduce the Risk of Hospitalization in Infants of Teenaged Mothers?
James P. Guevara, MD, MPH;
Josephine C. C. Young, MD, MPH;
Beth A. Mueller, DrPH
Arch Pediatr Adolesc Med. 2001;155:66-72.
ABSTRACT
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Objective To determine the risk of hospitalization associated with prenatal care
use and indicators of socioeconomic status and social support among infants
of teenage mothers.
Design Population-based case-control study.
Setting Nonfederal hospitals in Washington State.
Participants Infants born from 1987 to 1995 to mothers younger than 20 years were
identified using linked birth certificate–state hospital discharge data.
Cases consisted of 8052 infants who were hospitalized during the first year
of life at least 2 days after birth hospitalization discharge. An equal number
of controls, frequency matched on birth year and maternal age group, were
randomly sampled from among nonhospitalized infants.
Main Outcome Measure Hospitalization in the first year of life.
Results Infants with a father listed on the birth certificate or whose mothers
had commercial health insurance had a decreased risk of hospitalization (adjusted
odds ratios, 0.91 and 0.78, respectively; 95% confidence intervals, 0.83-0.99
and 0.71-0.85, respectively). Participation in state-funded pregnancy programs,
adequacy of prenatal care, or marital status did not affect the risk of hospitalization,
except among infants whose mothers received more than adequate prenatal care
(adjusted odds ratio, 1.15; 95% confidence interval, 1.03-1.29).
Conclusion Our results suggest that teenaged mothers who list a father on the birth
certificate or who have insurance, indicative of higher socioeconomic status,
may have a reduced risk of hospitalization for their infants. Teenaged mothers
who receive more than adequate prenatal care may have pregnancy complications
that place their infants at increased risk of hospitalization. The effect
of these protective factors should be clarified in future studies.
INTRODUCTION
TEEN PREGNANCY represents a major public health problem, with more than
500 000 births annually to teenage mothers in the United States.1, 2 Teen pregnancy is associated with many
adverse neonatal outcomes, including prematurity, low birth weight, and neonatal
death.3, 4, 5, 6
It is also recognized that infants born to teenage mothers are at increased
risk of hospitalization during the first year of life, relative to infants
of older mothers.7, 8, 9, 10
The majority of these hospital admissions are for potentially avoidable causes
such as gastroenteritis, respiratory infections, and injuries.8, 9, 10
Identification of factors associated with hospitalizations among infants
of teenaged mothers may aid the design of interventions to reduce this risk.
While previous studies have identified many risk factors associated with hospitalization,
such as lower socioeconomic status, maternal illness during pregnancy, presence
of congenital anomalies, low birth weight, male sex, and the presence of other
siblings in the family,7, 8, 9, 10
these studies have been unable to reliably identify all infants at greater
risk.10 Consequently, it has been recommended
that interventions be targeted to all teenaged mothers. However, it is unclear
what components should be included in such interventions.
We undertook a population-based, case-control study to examine the association
of prenatal care use and indicators of socioeconomic status and social support
with hospitalization in the first year of life among infants born to teenaged
mothers. We hypothesized that factors indicative of higher socioeconomic status,
social support during pregnancy, and adequacy of prenatal care would be associated
with a decreased risk of subsequent hospitalization for these infants.
PARTICIPANTS AND METHODS
SETTING
Data were obtained from the Washington State Department of Health (DOH),
which compiles information on all births and nonfederal hospital discharges
in Washington State on separate databases. The Comprehensive Hospital Abstract
Reporting System (CHARS) is a state-administered database that contains information
on all nonfederal hospital discharges in Washington State, beginning in 1987.
Hospital discharge data from these hospitals are reported to the DOH and are
edited for internal and logical consistency. The data are not routinely evaluated
for validity. The CHARS reports data on reasons for hospitalization (up to
9, using International Classification of Disease, Ninth
Revision [ICD-9] codes), length of stay, dates
of admission and discharge, primary payer, and procedure codes. The Birth
Events Records Database (BERD) is a state-administered database that links
birth certificate data for all infants born in nonfederal hospitals with hospital
discharge data related to the birth hospitalizations of mothers and their
newborns. The BERD reports information on date of birth; infant's, mother's,
and father's demographic characteristics; prenatal visits; prior pregnancies
and births; pregnancy and birth history; pregnancy program participation;
and the agency or type of payer to which the hospital charges were billed.
Linkage algorithms used by the DOH to create BERD have demonstrated a greater
than 98% correct match rate (personal communication, Vicki Hohner, MBA, Office
of Hospital and Patient Data Systems, DOH, November 24, 1999). Birth certificate
data undergo quality checks for completeness, validity, and internal consistency
before they are included in BERD. These checks are performed at the time of
data entry, at uploads of records to the main database, and at regular reviews
of the main database (weekly, quarterly, and annually) by DOH, other state,
and federal employees.
PARTICIPANTS
All singleton infants born in Washington State from 1987 to 1995 to
mothers younger than 20 years were identified using BERD. Cases consisted
of all infants who were hospitalized in Washington State during the first
12 months of life. Cases were identified by linking the personal identifier
code in the BERD file for the years 1987 to 1995 with that from the CHARS
file for the years 1987 to 1996. Only first hospitalizations were considered
for analysis. Cases were excluded if the hospitalization occurred within the
first 2 days after birth hospitalization, to avoid inclusion of hospitalizations
for possible birth complications. One control per case was selected at random
from among infants who were not hospitalized in the first year of life. Controls
were frequency matched to cases on maternal age group ( 17 years, 18-19
years) and year of birth. The study protocol was approved by the Human Subjects
Protection Committees at the University of Washington and the DOH.
OUTCOME MEASURES
The main outcome measure was hospitalization in the first year of life
for any reason. Hospitalizations among cases were classified by specific causes:
respiratory syncytial virus (RSV) lower respiratory tract disease (ICD-9 codes 466.1, 480.1); neonatal jaundice (ICD-9 code 774.6); non-RSV pneumonia (ICD-9 codes
480-486, except 480.1); gastroenteritis (ICD-9 codes
008, 009, and 558.9); viral infections (ICD-9 codes
045-079); dehydration (ICD-9 code 276.5); fever (ICD-9 code 780.6); injuries and poisonings (E-codes 800-999);
and other.
Associations between hospitalization and prenatal care or selected factors
related to socioeconomic status and social support were evaluated. The type
of health insurance billed as the primary payer for the mother's birth hospitalization
was used as a proxy indicator of socioeconomic status. Medicaid/charity care
represented lower socioeconomic status and health maintenance organization,
commercial, or other insurance represented higher socioeconomic status. Medicaid
managed care was classified as Medicaid. Adequacy of prenatal care was measured
using the Adequacy of Prenatal Care Utilization Index of Kotelchuck.11, 12 The Adequancy of Prenatal Care Utilization
Index categorizes prenatal care into 4 groups based on the timing of initiation
of prenatal care and the observed-to-expected number of prenatal care visits:
inadequate (initiation of prenatal care after the fourth month of gestation
or less than 50% of expected prenatal care visits); intermediate (initiation
of prenatal care before the fourth month of gestation and between 50% and
80% of expected prenatal care visits); adequate (initiation of prenatal care
before the fourth month of gestation and between 80% and 110% of expected
visits); and adequate plus (initiation of prenatal care before the fourth
month of gestation and greater than 110% of expected prenatal care visits).
Three variables were used as indicators of social support: marital status,
whether a father was listed on the birth certificate, and whether the mother
participated in state-administered pregnancy programs. To list a father on
a birth certificate in Washington State during the study period, the parents
must have been married or filed an affidavit of paternity. An affidavit of
paternity ensures that listed fathers are legally and financially responsible
for the care of their infants. In the few cases where paternity was in dispute,
a father could be listed after results of paternity testing. The following
state-administered programs were available to eligible pregnant women in Washington
State during the study period: Women, Infants, and Children; Aid to Families
With Dependent Children; First Steps, the Washington State Medicaid expansion
program; and other programs.
Other variables were considered in the analysis for their possible effect
on the variables of interest. These variables were derived from birth certificate
data and included birth year; infant sex; birth weight (<2500 g, 2500-4000
g, or >4000 g); estimated gestational age (<37 weeks or  37 weeks);
any congenital anomaly; any newborn medical condition; maternal age group
(<18 years or 18-19 years); maternal self-report of smoking; maternal self-report
of drinking during pregnancy (not routinely collected on birth certificates
until 1989); maternal race/ethnicity (white, black, Native American, Asian,
or Hispanic); urban or rural maternal residence; maternal gravidity and parity
(none, 1); history of prior induced pregnancy terminations (none, 1);
and history of any prior child deaths.
STATISTICAL ANALYSIS
Univariate associations between hospitalization and the primary variables
of interest were evaluated by the odds ratio (OR) with 95% confidence intervals
(CIs). Stratified analyses were performed using Mantel-Haenszel estimators,
with test-based CIs to control for potential confounding variables and assess
for interactions.13 The Breslow-Day Test was
used to evaluate the homogeneity of stratum-specific ORs.14
Only variables that markedly altered the risk estimates or resulted in significant
interactions were retained in the analyses. Logistic regression was used to
estimate the multivariate association between hospitalization and the primary
variables of interest while controlling for any other variables retained in
the analysis. Statistical analyses were performed using STATA, Release 5.0
for Macintosh (College Station, Tex).
RESULTS
A total of 74 382 singleton births to teenaged mothers were identified
from Washington State birth records during the study period 1987 to 1995.
Of these, 8492 infants of teenaged mothers were hospitalized within the first
year of life. We excluded 440 infants (5.2%) who were admitted within 2 days
of birth discharge to avoid hospitalizations for possible birth complications.
Thus, 8052 infants (10.8%) were hospitalized at least 2 days after hospital
discharge and constituted cases for analysis. These infants were hospitalized
for a variety of reasons, most commonly for RSV lower respiratory tract disease
(17.4%), jaundice (8.6%), non-RSV pneumonia (8.5%), viral syndrome (5.8%),
gastroenteritis (4.5%), and injuries and poisonings (3.8%). Most infants (84.2%)
incurred only 1 hospitalization. However, 927 (11.5%) had 2 hospitalizations
and 342 (4.3%) had 3 or more hospitalizations in the first year of life.
During the study period, rates of hospitalization for infants by birth
year remained fairly stable. Rates ranged from 102.4 per 1000 in 1987 to 116.8
per 1000 in 1991. Rates of hospitalization were similar for infants of mothers
17 years or younger and aged 18 to 19 years. During the study period, the
percentage of singleton births to teenaged mothers in Washington State remained
relatively constant (approximately 11%).
Most teenaged mothers in Washington State during the study period were
white, resided in urban areas, and had no prior pregnancies or live births.
Although most teenaged mothers (62.8%) were aged 18 to 19 years, the majority
of fathers (68.8%) were 20 years and older. There were 1111 (6.9%) teenaged
mothers who were younger than 16 years.
Mothers of cases and controls were similar with respect to paternal
age, maternal race other than Native American, previous induced abortions,
previous child deaths, and self-reported use of alcohol during pregnancy (Table 1). A greater percentage of mothers
of cases were Native American (7.1% vs 4.4%), resided in urban locations (64.1%
vs 60.9%), had a previous pregnancy (37.3% vs 30.7%) or live birth (25.1%
vs 19.8%), and reported smoking during pregnancy (36.9% vs 31.1%) relative
to mothers of controls.
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Table 1. Parental Characteristics of Infants of Teenaged Mothers Who
Were and Were Not Hospitalized During the First Year of Life*
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Most infants were born full-term, weight appropriate for gestational
age, and without congenital anomalies or newborn medical conditions (Table 2). A greater percentage of cases
were of low birth weight (10.9% vs 5.6%), premature (13.0% vs 7.1%), male
(58.4% vs 48.7%), diagnosed with a medical condition at birth (14.0% vs 11.3%),
or born with a congenital anomaly (5.0% vs 2.7%) relative to controls.
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Table 2. Characteristics of Infants of Teenaged Mothers Who Were and
Were Not Hospitalized During the First Year of Life*
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Most teenaged mothers (58.8%) began prenatal care within the first 3
months of gestation. A greater percentage of mothers of cases received more
than adequate prenatal care (25.4% vs 21.6%) relative to mothers of controls
(Table 3). Infants whose mothers
received more than adequate prenatal care had an increased risk of hospitalization
(OR, 1.15; 95% CI, 1.03-1.29; adjusted for gestational age, socioeconomic
status, marital status, listing a father, and pregnancy program participation)
relative to infants whose mothers received inadequate prenatal care. Infants
whose mothers received intermediate or adequate prenatal care did not have
a risk of hospitalization different from infants whose mothers received inadequate
prenatal care.
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Table 3. Adjusted Risk of Hospitalization Associated With Indicators
of Prenatal Care, Social Support, and Socioeconomic Status Among Infants of
Teenaged Mothers*
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Regarding indicators of social support (Table 3), approximately one quarter of teenaged mothers in the study
were married (28%). Slightly fewer mothers of cases than controls were married
(27.0% vs 29.1%). A majority of infants had a father listed on the birth certificate
(53.2%). A slight majority of mothers who listed a father on the birth certificate
were married (51.5%). A smaller percentage of cases had a father listed on
the birth certificate (51.6% vs 54.7%) relative to controls. One third of
teenaged mothers (34.4%) participated in state-administered pregnancy programs.
Among program users, most participated in Women, Infants, and Children (84.9%),
followed by First Steps (40.5%), Aid to Families With Dependent Children (19.2%),
and other miscellaneous programs (19.1%). A slightly greater percentage of
mothers of cases than controls participated in these programs (35.3% vs 33.6%).
Infants with a father listed on the birth certificate had a decreased risk
of hospitalization relative to infants without a father listed on the birth
certificate (OR, 0.91; 95% CI, 0.83-0.99, adjusted for gestational age, prenatal
care, socioeconomic status, marital status, and pregnancy program participation).
Infants whose mothers were married or whose mothers participated in pregnancy
programs did not have a risk of hospitalization different from those whose
mothers were single or whose mothers did not participate in pregnancy programs.
Most teenaged mothers (72.3%) had Medicaid insurance or charity care
listed as the primary payer at the time of birth hospitalization. A greater
percentage of mothers of cases than controls had Medicaid insurance or received
charity care (Table 3). Mothers
of cases had significantly lower mean years of education (10.3 vs 10.5 years)
than mothers of controls, but the difference was clinically insignificant.
Data on maternal education were not routinely reported on birth certificates
in the state until 1992. Infants whose mothers had commercial, health maintenance
organization, or other health insurance listed as the payer on the birth certificate
had a decreased risk of hospitalization (OR, 0.78; 95% CI, 0.71-0.85; adjusted
for gestational age, prenatal care, marital status, listing a father, and
pregnancy program participation) relative to infants whose mothers had Medicaid
insurance or charity care listed as the payer.
Teenage mothers who were younger than 16 years at the time of birth
hospitalization were analyzed separately. There was no significant difference
between cases and controls in the percentage of teenage mothers younger than
16 years (6.8% of cases vs 7.0% of controls). Teenage mothers younger than
16 years were more likely to have inadequate prenatal care (38% vs 27%) and
use pregnancy programs (39.5% vs 34.1%) than older mothers. Moreover, teenage
mothers younger than 16 years were less likely to be married (6.1% vs 29.6%)
or to list a father on the birth certificate (31.2% vs 54.8%) than older mothers.
Infants of teenaged mothers who were younger than 16 years had risk estimates
that were similar to those obtained from the entire sample, except that the
point estimate obtained for the risk of hospitalization associated with being
married increased (adjusted OR, 1.63), and the point estimate obtained for
the risk of hospitalization associated with more than adequate prenatal care
decreased (adjusted OR, 1.03). None of the point estimates from this subgroup
analysis was significant.
A subgroup analysis was undertaken to evaluate the effect of infant
factors known or suspected to increase the risk of hospitalization (low birth
weight, prematurity, congenital anomalies, and neonatal conditions) on adjusted
risk estimates. To assess whether these findings were consistent among infants
without these characteristics, the analysis was repeated after restricting
infants to those who were of normal birth weight (2500-4000 g), term gestation
(>37 weeks), and without congenital anomalies or newborn medical conditions.
A total of 7923 infants (49.2%) with at least 1 risk factor were omitted from
this subgroup analysis. The resulting risk estimates did not differ markedly
from those obtained with the entire sample.
A second subgroup analysis was undertaken to evaluate whether hospitalizations
for possible birth complications influenced adjusted risk estimates. To evaluate
for this, the analysis was repeated using only cases whose hospital admission
occurred after 28 days of life. A total of 2313 infants (28.7%) who were hospitalized
within the first 28 days of life were omitted from this subgroup analysis.
There were no appreciable changes in the risk estimates from those obtained
with the entire sample.
The risks of hospitalization for specific conditions were evaluated.
The specific conditions included RSV lower respiratory tract disease, jaundice,
non-RSV pneumonia, and injuries and poisonings (E-codes). The risks of hospitalization
for RSV lower respiratory tract disease (N = 1398) were similar to the overall
risks of hospitalization, except that the risk associated with receiving more
than adequate prenatal care increased (adjusted OR, 1.28; 95% CI, 1.05-1.57).
The risks of hospitalization for jaundice (n = 694) were similar, except that
the risk associated with receiving more than adequate prenatal care increased
(adjusted OR, 1.85; 95% CI, 1.42-2.42) and the risk of being married became
significant (adjusted OR, 1.36; 95% CI, 1.08-1.72). The risks of hospitalization
for injuries and poisonings (n = 306) or non-RSV pneumonia (n = 685) were
similar to the overall risks of hospitalization in the entire sample.
COMMENT
We performed, to our knowledge, the first population-based analysis
of infants of teenaged mothers and the risk of hospitalization in the first
year of life associated with possible protective factors. We found that infants
whose mothers have commercial insurance as the primary payer had a 22% reduction
in the risk of hospitalization. We also found that infants whose fathers were
listed on the birth certificate had a 9% reduction in the risk of hospitalization.
This latter risk reduction represents more than $3.1 million in averted hospital
charges in Washington State during the study period based on mean hospital
charges. We found that marital status, participation in state-administered
pregnancy programs, and adequacy of prenatal care did not affect the risk
of infant hospitalization except among women receiving the highest category
of prenatal care. Here, infants whose mothers received more than adequate
prenatal care had a 15% increased risk of hospitalization. This increased
risk occurred primarily among those infants hospitalized for RSV lower respiratory
tract disease and newborn jaundice. Risks of hospitalization did not vary
appreciably among healthy term infants of normal birth weight or those hospitalized
at older than 28 days. Risks of hospitalization varied slightly between mothers
younger than 16 years and those who were older.
Findings from the literature suggest that teenaged mothers who receive
social support may reduce their risk of many adverse pregnancy outcomes, such
as low birth weight.15, 16, 17
However, the few studies to date reporting on hospitalization among infants
of teenaged mothers have not examined the effect of paternal social support.7, 8, 9, 10 Studies
reporting on other outcomes have found that teenaged mothers whose partners
participate in the care of their children have more positive child-rearing
attitudes18, 19 and less depressive
symptoms.20 In our study, we found that infants
who had a father listed on the birth certificate had a decreased risk of hospitalization
while infants whose mothers were married or participated in pregnancy programs
did not have risk different from infants whose mothers were not. In most cases,
teenaged parents must be legally married or file an affidavit of paternity
to list a father on the birth certificate in Washington State. Fathers who
complete an affidavit of paternity become legally and financially responsible
for the care of their children. We speculate that teenaged mothers in this
study who listed a father on the birth certificate may have been involved
in more stable relationships that support the care of their children. However,
we did not specifically measure paternal social support, and this finding
must be weighed against the finding that marital status was not associated
with risk of hospitalization.
The finding of a decreased risk of hospitalization associated with an
indicator of higher socioeconomic status, use of commercial insurance, is
consistent with a large body of evidence supporting the association of lower
socioeconomic status and adverse pregnancy outcomes.6, 8, 21, 22
The reasons for such a finding are complex and are likely to be related to
many factors associated with lower socioeconomic status, such as poor access
to primary care, transportation difficulties, lack of social supports, cultural
barriers, and high-risk behaviors.23
Although other studies have shown that adequate prenatal care can reduce
the risk of adverse pregnancy outcomes,12, 16, 24
we did not find a significant association between the level of prenatal care
and later risk of infant hospitalization, except for those who received more
than adequate prenatal care. Adequate prenatal care reflects both sufficient
access to care and knowledge and motivation on the part of women to appropriately
use care. It may be that prenatal care is not a good proxy measure of health
care access after delivery because of changes in insurance coverage. However,
more than adequate prenatal care may identify teenaged mothers who have pregnancy-related
complications that place their child at greater risk of hospitalization in
the first year of life.12
Our study has several important strengths. First, our study was population
based and identified all singleton infants of teenaged mothers in Washington
State; previous studies have not been population based. Second, we used a
comprehensive statewide hospital discharge database that enabled us to identify
virtually all cases of infants of teenaged mothers who were hospitalized.
Only those few infants whose mothers moved out of state or went across state
lines to have their infants hospitalized would have been missed. Previous
studies employing survey techniques to classify cases may be limited by inaccuracies
in maternal recall of hospitalizations in the first year of life.25 Third, we relied on birth certificate information
gathered at the time of delivery to categorize variables of interest. Previous
studies using survey techniques may be limited by recall bias, in which cases
they may differentially recall past events relative to controls. Fourth, we
were able to identify a large number of cases that enabled us to have sufficient
power to detect small associations. Previous studies have been smaller and
may not have had sufficient power to detect the small associations that we
observed in this study.
Our study does have several limitations. First, the use of administrative
databases in general may contain errors in diagnostic coding. However, there
is no reason to suspect that differential misclassification of information
occurred preferentially in either cases or controls. Any bias in such an instance
would be towards the null. Second, information on health insurance at the
time of rehospitalization was not available for controls, so we used the primary
payer for the birth hospitalization as an indicator of socioeconomic status.
Since insurance status may change from the time of birth hospitalization to
rehospitalization, any such changes may alter the risk of hospitalization
associated with this variable. For cases, we found that 86.8% of those originally
classified with Medicaid insurance or receiving charity care at the time of
birth hospitalization were similarly classified at the time of rehospitalization,
suggesting that any changes in health insurance in the study population were
probably small. Third, information on the health status of infants at the
time of hospitalization was not available. However, we did restrict the analysis
to those infants who were without prematurity, low birth weight, congenital
anomalies, and newborn medical conditions, which are the main determinants
of poor infant health status in the first year of life. Results of the subgroup
analysis were not different from those results obtained from the entire population.
Fourth, identification of infants hospitalized within the first month of life
may include hospitalizations for birth complications. Restriction of cases
to those infants hospitalized at older than 28 days did not alter risk estimates
appreciably. Fifth, our use of insurance type as a proxy indicator of socioeconomic
status may have limited utility. However, we found that subjects with Medicaid
or charity care had a significantly lower mean income ($22 450 vs $24 751; P<.001) than subjects with health maintenance organization,
commercial, or other insurance types. Moreover, Medicaid managed care was
not initiated in the state until 1993, so its effect was not apparent during
most of the study period. Coding algorithms from the DOH specified that Medicaid
managed care was to be coded as Medicaid on all payer fields. Sixth, information
on hospitalizations from federal hospitals in the state was not included in
the analysis. Births and hospitalizations that occur in federal hospitals
(eg, military facilities) represent a small percentage of the total. It is
unclear what effect the absence of these hospitalizations has on overall risk
estimates.
This study has possible implications for the design of interventions
to reduce the risk of hospitalization among infants born to teenaged mothers.
Although the incorporation of social support interventions before delivery
may reduce adverse pregnancy outcomes, it is unclear whether such interventions
after delivery may affect adverse infant outcomes such as hospitalization.
Our data suggest a reduced risk of infant hospitalization among teenaged mothers
who list a father on the birth certificate. Further studies of infant hospitalization
that incorporate more explicit measures of social support from partners and
family members may help to clarify these findings, particularly in the context
of marital status.
AUTHOR INFORMATION
Accepted for publication September 6, 2000.
Presented in part at the regional meeting of the Ambulatory Pediatrics
Association, Carmel, Calif, January 31, 1999.
We thank the Washington State Department of Health, for providing access
to these data and William O'Brien, BS, for his assistance in the programming
of the dataset.
From the Departments of Pediatrics, School of Medicine (Drs Guevara
and Young), and Epidemiology, School of Public Health and Community Medicine
(Dr Mueller), University of Washington, Seattle.
Corresponding author: James Guevara, MD, MPH, Division of General
Pediatrics, Children's Hospital of Philadelphia, 34th and Civic Center Boulevard,
Philadelphia, PA 19104.
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25. McCormick MC, Brooks-Gunn J. Concurrent child health status and maternal recall of events in infancy. Pediatrics. 1999;104(5, pt 2):1176-1181.
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