Abstract
Using a retrospective cohort study design, we report empirical evidence on the effect
of parental socioeconomic status, primary care, and health care expenditure
associated with preterm or low birth weight (PLBW) babies on their mortality
(neonatal, postneonatal, and under-five mortality) under a universal health care
system. A total of 4,668 singleton PLBW babies born in Taiwan between Jan 1 and
Dec 31, 2001 are extracted from a population-based medical claims database for a
follow-up of up to five years. Multivariate survival models suggested the positive
effect of higher parental income was significant in neonatal period but diminished in
later stages. Consistent inverse relationship was observed between adequate
antenatal care and three outcomes: neonatal HR: 0.494, 95% CI: 0.312-0.783;
postneonatal HR: 0.282, 95% CI: 0.102-0.774; and under-five HR: 0.575, 95% CI:
0.386-0.857. Primary care services uptake should be actively promoted, particularly
in lower income groups, to prevent premature PLBW mortality.
Keywords: preterm birth, low birth weight, socioeconomic status, health care
disparities, premature mortality
Abbreviated Short Title: Socioeconomic status, primary care, and preterm low birth
weight survival under social health insurance
1
Introduction
From 1971 to 2006, neonatal mortality and infant mortality rates in Taiwan have
dropped from 6.72 to 3.01 per 1,000 live births, and 16.56 to 5.35 per 1,000 live
births, respectively, while a gradual increase in prevalence of preterm or
low-birth-weight (PLBW) births is observed - despite Taiwan’s economic standing that
supports a sufficient healthcare capacity.1,2 Taiwan’s sex ratio (SR) at birth, estimated
at 1.08 in 2001, also lies above biological norm (only slightly above 1). This pattern is
consistent with skewed SRs found in Asian countries where the cultural context
favors birth of boys over girls and could suggest sex-based abortion.3,4 Most
Taiwanese mothers still live under a traditional norm where son is to be produced to
become the family heir and daughter is to be married outside family. However, a
study conducted in Taiwan overruled the possibility of selective abortion for the
skewed SR and confirmed that the sex imbalance occurs as early as midtrimester.5
Since disclosure of prenatal fetal sex is prohibited in Taiwan, there can be other
factors that can attribute to the SR difference such as birth order, parental age, and
environmental conditions.6,7
PLBW birth is a major risk factor for infant and child mortality. Preterm births
are those that occur at less than 37 complete weeks of gestation. LBW births refer to
babies born weighing 2500g or less, regardless of gestational age. McCormick8 found
2
that preterm births account for 75% of perinatal mortality and suggested that
neonatal mortality can be effectively diminished by efficacious antenatal services
that prevent LBW births. This was confirmed by various subsequent studies.9,10 In
Taiwan, prevention of child mortality in the country, however, still falls short of the
highest attainable standard in comparison with other industrialized countries.11 This
leads to our speculation that lack of primary care (PC) uptake or socioeconomic
status may contribute to this pattern.
Socioeconomic factors like parental social class can exert influence on the
survival of PLBW babies, as a cumulative effect of income on health.12,13 Two
hypotheses have been suggested in support of this association: first, children in
families with higher income and education have better use of health services as a
result of advanced social support and knowledge about health to cushion the impact
of health risks14; second, children in socioeconomically-disadvantaged families are at
more frequent exposure to injuries and health hazards.15 Low level of household
income generates financial barrier for accessing health services for children in need,
creating disproportionate accessibility across different socioeconomic classes.
Presently, there is a scarcity of literature on the effect of socioeconomic status
(SES) and primary care on neonatal, infant and child mortality of PLBW babies for
developed countries. In developing countries like Cuba, an universal health care
3
system with emphasis on PC has helped to reduce LBW prevalence which, in turn,
lowered the population’s child and infant mortality.16 Inverse effect of PC such as
attended births by skill professionals on infant and child mortality has been
demonstrated in a study done on 102 low- and middle-income countries.17 Another
study examining socially disadvantaged, young unmarried mothers in Malaysia
showed that prenatal care visits serve as a risk factor for adverse birth outcomes.18
Even in areas with considerable social gaps, an increased number of PC physicians
can help to ameliorate LBW and infant mortality in the United States.19 Nevertheless,
whether unfavorable effect on birth outcome exerted by low-SES can be
overshadowed by sufficient uptake of PC is under-explored at the individual-level in
the scientific literature
Unlike previous existing studies, this study investigates Taiwan’s social health
insurance that supports a UHC system that has been implemented for almost two
decades. Its comprehensive benefit package included an array of available PC
services that could be more effectively promoted and utilized, especially for the
socioeconomically-disadvantaged. Hence, we hope to look into predictors of PLBW
survival with consideration of the UHC system and household socioeconomic factors.
Using a retrospective cohort study design, we specifically examine the extent of
PLBW health disparities and the effect of parental SES, PC, and health care
4
expenditure associated with PLBW babies on their mortality at different stages of
development.
Method
Data source and study cohort
We include PLBW babies born between Jan 1 and Dec 31, 2001 extracted from the
National Health Insurance Research Database (NHIRD) using the International
Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes 764
and 765, and V21.3. Here we examine the pooled sample of preterm and LBW babies
(i.e., PLBW) due to the indistinguishable nature of the ICD-9-CM codes.
Maintained by the National Health Research Institutes (NHRI) in Taiwan, the
NHIRD is a complete NHI claims-based database accessible to the public upon
application which has been used to monitor and assess various policy
implementations.20 Unique identification numbers are encrypted for confidentiality
but remain consistent throughout all outpatient and inpatient claim files, for us to
trace and construct variables by linking the files to obtain information regarding
sociodemographics, medical history and diagnoses. Financed through payroll-based
premiums and direct government funding, the NHI provides a comprehensive benefit
5
package including ambulatory care, inpatient care, prescription drugs, dental care,
and preventive care like antenatal care.21,22 Today, more than 99% of population is
enrolled in the single-payer program.
Of the 7,913 live PLBW births, 6,038 (76.3%) are selected based on their
enrollment in the NHI as dependents of their parents (immediate household
members) since their birthday, and their parents’ continuous NHI enrollment
throughout the observation period postpartum for ascertainment of their
employment status. After removal of multiple births (n=1,370), a total of 4,668 PLBW
are identified: employed mothers (n=2,467) and unemployed mothers (n=2,201). A
total of 7,907,230 person-days are observed. Babies as dependents of household
members other than their parents, and those with unusual birth dates and maternal
age of delivery are excluded. Also excluded are stillbirths (ICD-9-CM: 646.0. 651,
652.6, 656.4. 678.1 V27.1-V27.7). The cohort is followed longitudinally for up to five
years until Dec 31 2006 or up to the time of ‘event’. This study has been granted
ethics approval by the Institutional Review Board at the China Medical University
Hospital.
Data collection
Dependent variables
6
Primary end-points of this study are neonatal mortality (<28 day), postneonatal
mortality (28 day–1 year), and under-five mortality (0-5 year). Because mortality
rates and their risk factors are remarkably different among these stages, three
sub-periods are defined, each carrying out a separate model of analysis. Death or
‘event’ is defined by admission records, either by in-hospital death or discontinuation
of insurance status within 30-day of discharge from the hospital, which is proven to
be a good proxy for survival.23,24 For these individuals, index date is their date of birth
and exit date of insurance enrollment marks the end of their observation period.
Loss-of-insurance status is a suitable proxy for mortality in this instance because first,
loss of insurance after hospitalization is a reasonable hypothesis when considering a
newborn baby born PLBW is admitted right after birth and did not survive after a
period of hospitalization. Second, with this proxy, we are able to observe mortality of
these PLBW babies across three periods which is consistent with the epidemiological
pattern in Taiwan (i.e., highest within 28 days after birth and declines over time).
However, any loss-of-insurance status outside these criteria is treated as censored
observation.
Independent variables
7
We specify four general categories of measures for independent variables. In the
sociodemographic category, the parent premium is used for ascertainment of the
parental SES and the city of enrollment is used to define the geographical location. It
is generally accepted that parental SES is a good and valid indicator for early
childhood socioeconomic position. Given the almost 100% coverage of the Taiwan
NHI, we believe that the payroll-based premium may well be one of the best
available nationwide data that can be used to infer parental income.
There are two scenarios under which babies are dependents of parents’
insurance – a) mother as the insurance payer: mother is employed and the baby is
mother’s dependent due to relative lower payroll-based premium compared to the
father and; b) father as the insurance payer: father is employed and is the head
insured person of the household for his spouse and children (i.e., mother most likely
does not have a job). Owing to the distinct nature of these types of payroll, we
stratify our analyses according to the insurance enrollment status of mothers at time
of delivery: hereafter refer to as employed (former) or unemployed (latter). This is
performed so that households with same parental employment conditions would be
compared.
In the PC category, government-subsidized antenatal care is calculated within
37-week before the index date for study cohort. We specify receipt of antenatal care
8
as having at least four antenatal care visits because this number of visits confine to
the first two trimesters of gestation which are crucial for prevention of adverse
delivery outcome, whereas visits in the third trimester are mainly for detection and
treatment of problems whose frequency may vary depending on conditions.8
Similarly, government-subsidized neonatal care and immunization are defined after
neonatal period during which major development examinations and vaccinations are
received.
For health expenditure, we focus on the cost-sharing component of health care
financing. Two parameters for health expenditure are derived for analysis: total
out-of-pocket (OOP) health spending as a percentage of parental income and total
OOP health spending as a percentage of total health expenditure (THE). The former
illustrates the proportion of parental income attributed to health care use (ability to
pay) and the latter depicts relative financial contribution by individuals from the
system standpoint (affordability of care). OOP expenditures are calculated separately
for each sub-period by service type. We also consider confounders such as maternal
comorbidities (identified within 365.25 days before index date) and physiological
conditions originating in the perinatal period (Supplementary Table 1).
Data analysis
9
Descriptive analysis
Frequency distributions of sociodemographic and physiological attributes are
reported for the PLBW birth cohort from 2001, and stratified for employed and
unemployed mothers (Table 1). Intra-group comparisons are performed using
Student’s t-test, Chi-square test and Fisher’s exact test depending on nature of
variables.
For period-sensitive predictors, total observation period is reported in
person-days (Supplementary Table 2). Health service utilization and expenditure
variables are dichotomized into low and high groups using medians of the study
cohort. Distribution of resources across income and geographical groups are
illustrated in Figure 1.
Bivariate analysis
We are interested in the relative impact of neighborhood and individual factors on
PLBW survival. Effects of relative parental income (individual-level) and
neighborhood (community-level) on neonatal mortality are jointly explored in a
bivariate Cox proportional hazard regression model stratified by maternal
employment status (Figure 2). In exploring the effect of income inequality, we derive
relative parental income (parental income divided by median income).
10
Multivariate analysis
Survival analysis using Cox proportional hazards model with time-dependent
covariates (parental income and geographical area of enrollment) is used to assess
influence of parental SES and other risk factors on three outcomes. The assumption
of proportionality for each of the models is validated.
Two models are developed with sequential inclusion of predictors: Model 1
included parental income and OOP expenditure as share of parental income while
controlling for baby sex, geographical area, maternal age and comorbidities,
complications at birth, and health service utilization; Model 2 is equivalent to Model
1 with further adjustment for PC use. Health service utilization is adjusted to take
into account any additional support or accessibility to care provided by more health
conscious parents that would influence PLBW survival rate. Test for interaction does
not reveal higher service utilization (outpatient and inpatient) is associated with
greater OOP expenditure, suggesting that inclusion of interaction terms in the final
multivariate model is not required (Model 2 in Table 2). Analyses are performed with
exclusion of multiple births with consideration of the biased effect caused by
immediate physiological factors not related to SES, but results inclusive of multiple
births are also provided (Supplementary Tables 3-4). Multicollinearity tests are
11
conducted to ensure no violation of models is evident. For all statistical analyses,
P-value of less than 0.05 is considered to be statistically significant. All analyses are
performed using SAS statistical package version 9.2 (SAS Institute, Cary, NC).
Results
Descriptive analysis
Table 1 shows the baseline characteristics of the singleton children born PLBW.
Distribution of parental income at birth is different when comparing PLBW babies
between employed and unemployed mothers, where the latter group has a higher
mean income (NTD26050.8 vs. NTD24633.1; USD1≈NTD33.8 in 2001) – a difference
of roughly 6%. For time-sensitive variables, very high inpatient OOP expenditure as
share of parental income was spent in the neonatal period and declined as time
progressed (Supplementary Table 2).
A slightly higher proportion of richest 20% (Q5) mothers received adequate
prenatal care compared with other income groups while the poorest mothers spent
the highest proportion of income on health within 28 days after birth (Figure 1). In
general, excess mortality rates are highest among neonatal PLBW babies born in the
12
bottom two income quintiles or in the south and east regions of the country (data
not shown).
Bivariate and multivariate survival analysis
When jointly considered the effect of individual- and community-level factors on
neonatal mortality in bivariate analysis, singleton PLBW babies born to employed
mothers with relative low income residing in the south region are at highest risk
(hazard ratio (HR): 3.623; P<0.001) (Figure 2).
In Model 1 of the multivariate analysis (Table 2), relative high income is
associated with lower mortality risk consistently through neonatal, postneonatal, and
under-five year periods in employed mothers (HR: 0.528, 95% CI: 0.326, 0.857,
P<0.01; HR: 0.295, 95% CI: 0.113, 0.769, P<0.05; HR: 0.505, 95% CI: 0.334, 0.765,
P<0.01, respectively). High outpatient and inpatient OOP as share of parental income
is also consistently associated with lower mortality risks for the three periods as
compared to relative low group.
Further adjustment of PC use in Model 2 diminished the effect of relative high
parental income in employed mothers, but suggested a profound inverse relationship
between adequate antenatal care and neonatal mortality, postneonatal mortality,
and under-five mortality (HR: 0.494, 95% CI: 0.312, 0.783, P<0.01; HR: 0.282, 95% CI:
13
0.102, 0.774, P<0.05; and HR: 0.575, 95% CI: 0.386, 0.857, P<0.01, respectively).
Furthermore, high neonatal care and high subsidized immunization are significant
protective agents for postneonatal and under-five mortality in both employment
groups, respectively. For OOP expenditure (inpatient and outpatient), its inverse
effect appear to persist from neonatal period up to five years of age in PLBW children
of both groups (i.e., an employed or unemployed mother with relative high OOP
expenditure as a proportion of parental income will have a lower likelihood of having
a singleton PLBW baby experiencing premature death compared to relative low OOP
spending counterpart).
Discussion
Main findings of this study
Our objective is to investigate whether after the implementation of universal health
care system in Taiwan, distribution of PLBW survival will be equitable in the presence
of an upstream factor like social position by income when controlling for PC uptake
and OOP health expenditure. We demonstrated that in a health system financed
partly by direct payments at point of service, inequalities in service utilization and
OOP expenditure up to five years of age still exist for PLBW babies across SES groups
14
and geographical regions. This implies uneven distribution of resources amongst our
population in spite of the universal coverage insurance. Access to PC, for instance, is
enjoyed most by the better-off while OOP payments seem to generate the most
financial burden in poorer households. More importantly, PC services are positively
associated with PLBW survival up to five years after birth, while high relative parental
income exerts an impact only in the first 28-days.
What is already known on this topic
SES is an important input in the child health production. Effect of parental
income on children’s health has been well established.12-15,25-27 SES can mitigate the
consequences of health shocks, and higher SES can augment the chance of children
recovering from negative health conditions.26 Cost-sharing, alternatively, reduces
health care accessibility more among the poor than the rich. Distributions of
long-term medication use and health resource use are found to be more
concentrated amongst higher social classes,25,28 and disparities in physician visits
across different SES classes are considerable in industrialized countries with heavy
reliance on private financing like patient cost-sharing.29 So we can argue if SES were
to exert an effect on PLBW survival, it would be that the high-SES mothers had higher
access to helpful resources during gestation and early intervention programs for
15
PLBW babies than low-SES mothers.15,30 Thus, health status of low-SES children could
eventually catch up to that of high-SES children. This conclusion indeed supports our
finding that the effect of relative parental income is significant in the neonatal period
but dissipates thereafter for PLBW children.
Studies have also highlighted the importance of PC provision in enhancing
children’s health and avoiding premature deaths in both developed and less
developed economies.31-34 Health systems that center around PC have better health
outcomes.32,33 The role of PC is multifaceted. It not only aids in early prevention of
disease, but also increases access to health services for relatively disadvantaged
groups. Our results consent with this argument when we observe the negative
association between adequate uptake of antenatal care, neonatal care, immunization
and PLBW mortality even controlling for individual-level SES. However, we also agree
that gaps in the receipt of ample PC services persist in many areas.35
Limitations of this study
We observed a high SR of 1.23 for our PLBW cohort. The reason for this could be
the cultural-based sex-selectivity that is amplified in PLBW babies, i.e., more
sex-based abortions occur for female PLBW babies than male PLBW babies given the
adverse birth outcome. Although prenatal sex-screening is banned in Taiwan, it may
16
not have been well enforced in 2001 and the determination of sex would affect
parents’ choice for abortion. Since female PLBW babies are more likely fall out of our
observation and not being included in our selection, our observed mortality could be
underestimated.
Another caveat from our selection criteria is that we did not include 1,875
(23.7%) babies for reasons of trying to derive an accurate parental income measure:
we excluded 1) babies who are not NHI dependents of their father or mother (we
cannot infer parental income); or 2) babies who are NHI dependents of their father
or mother but their enrollment did not persist throughout the observation period (to
avoid unusual cases of frequent, irregular exit-and-re-enrollment activity within the
5-year observation and can greatly fluctuate the observed SES).
Smoking in mothers could not be identified. Instead, we controlled for the effect
of chronic lung diseases which is a good indicator for chronic smokers.36 Because
Taiwan holds low infant mortality and under-five mortality, data from bigger cohort
collected from multiple years instead of one year could be more favorable, but this
would restrict the length of observation period due to data availability which we did
not wish to forgo.
What this study adds
17
In spite of these caveats, we find only few published research investigating
socioeconomic disparities in PLBW child mortality with relation to system-level and
individual-level predictors. Our findings support the universal coverage of essential
PC services for pregnant women, babies and infants irrespective of individual SES in
order to improve PLBW survival. Furthermore, we measured long-term impacts of
relative poverty. We derived parental SES using salary-based premium paid by each
enrollee which is a reliable measure of material living standards. We further
considered relative income a measure of social exclusion since it was proposed that
wellbeing is more closely related to relative income than absolute income in rich
countries.37 The large sample size and adequate length of follow-up time allow for an
invaluable opportunity to examine predictors of the postnatal survival of a PLBW
birth cohort.
Interestingly, we observe that PLBW babies who incurred high inpatient and
outpatient OOP payments as a proportion of their parental income resulted in better
odds of survival. This indicates that the survival of a less physically-sound PLBW baby
depends not so much on how large their parents' financial sacrifice is, but on how
much money is spent on the baby, independent of parental income. This is not in
alignment with what literature has been suggesting about catastrophic health
spending leading up to poorer and inequitable health.38,39 We would like to interpret
18
this as these PLBW babies are at greatly heightened risk of life-threatening illness at
baseline comparing with general population. Hence, we see that ‘paying for health
care’ is beneficial for their survival at least before reaching their fifth birthday. In the
treatment-oriented Taiwanese society, it is possible that parents would seek extra
care even if it exceeds their health spending for the cost of saving their PLBW child.
Conclusion
In concluding, we find that social gradient in health service utilization exists in
Taiwan’s social health insurance system and that sufficient PC uptake can positively
associate with survival of high-mortality-risk PLBW babies up to five years after birth,
independent of parental income. This finding confirms that even under universal
health care scheme, the use of PC services should be actively promoted especially in
the lower SES groups.
19
Acknowledgements
This study is based on data provided and managed by the Taiwan National Health
Research Institutes (NHRI). We thank the NHRI for providing NHIRD and
administrative support for research purposes (Project No. 98348).
Declaration of Conflicting Interest
The authors declare there is no conflict of interest.
Funding
This work was supported in part by the National Science Council, Executive Yuan,
Taiwan (NSC 101-2314-B-039-016).
20
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23
Table 1. Descriptive profile of sociodemographic and physiological attributes for study cohort at baseline in 2001.
.
Characteristic
All PLBW
Employed mothers Unemployed mothers
n=4668
n=2467
n=2201
Person-days
7,907,230
4,211,841
3,695,389
Sociodemographics
Sex, no. (%)
Female
2093 (44.84)
1109 (44.95)
984 (44.71)
Male
2575 (55.16)
1358 (55.05)
1217 (55.29)
Geographical area, no. (%)
**
North
2273 (48.69)
1276 (51.72)
997 (45.30)
Centre
1065 (22.81)
502 (20.35)
563 (25.58)
South
1121 (24.01)
574 (23.27)
547 (24.85)
East
175 (3.75)
101 (4.09)
74 (3.36)
Islands and others
34 (0.73)
14 (0.57)
20 (0.91)
Maternal age at delivery, no. (%), years
**
<20
159 (3.41)
62 (2.51)
97 (4.41)
20-29
2357 (50.49)
1097 (44.47)
1260 (57.25)
30-39
2015 (43.17)
1220 (49.45)
795 (36.12)
≧40
137 (2.93)
88 (3.57)
49 (2.23)
Parental income at birth, no. (%), NTD
**
Q5 (≦16500)
919 (19.69)
414 (16.78)
505 (22.94)
Q4 (16501-19200)
834 (17.87)
502 (20.35)
332 (15.08)
Q3 (19201-25200)
667 (14.29)
417 (16.90)
250 (11.36)
Q2 (25201-38200)
1231 (26.37)
631 (25.58)
600 (27.26)
Q1 (>38200)
1017 (21.79)
503 (20.39)
514 (23.35)
Parental income at birth, mean±SD (NTD)
25301.6±14737.4
24633.1±12885.7
26050.8±16539.7 *
Physiological attributes
Maternal comorbidities, no. (%)
Diabetes mellitus
280 (6.00)
197 (7.99)
83 (3.77)
**
Chronic renal disease
6 (0.13)
5 (0.20)
1 (0.05)
Hypertension
325 (6.96)
234 (9.49)
91 (4.13)
**
Chronic lung disease
82 (1.76)
55 (2.23)
27 (1.23)
*
Complications at birth, no. (%)
Congenital anomalies
1402 (30.03)
739 (29.96)
663 (30.12)
Birth trauma
95 (2.04)
45 (1.82)
50 (2.27)
RDS
1510 (32.35)
785 (31.82)
725 (32.94)
Note: Values are n (%) or mean ± SD.
*P<0.05; **P<0.01
PLBW - preterm low birth weight; NTD - New Taiwan Dollar; Q - quintile; RDS - respiratory distress syndrome
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Table 2. Period-specific hazard ratios using Cox Proportional Hazards Model for the PLBW mortality at 0-28 day, 28 day-1 year, and 0-5 year observation periods in
employed and unemployed mothers.
Employed Mothers
Variable†
Model 1
HR (95% CI)
Model 2
HR (95% CI)
Unemployed Mothers
Model 1
HR (95% CI)
Model 2
HR (95% CI)
<28d
0.728 (0.476-1.116)
0.743 (0.486-1.135)
Relative income
0.528 (0.326-0.857)**
0.569 (0.347-0.931)*
0.766 (0.472-1.242)
Antenatal care (at least 4 times)
-0.494 (0.312-0.783)**
-OOP Outpatient (as proportion of parental income)
0.000 (0.000-)
0.000 (0.000-)
0.000 (0.000-)
0.000 (0.000-)
0.661
(0.420-1.042)
0.691 (0.439-1.087)
OOP Inpatient (as proportion of parental income)
0.473 (0.284-0.787)**
0.479 (0.288-0.798)**
28d-1yr
Relative income
0.295 (0.113-0.769)*
0.485 (0.163-1.442)
0.815 (0.369-1.802)
0.703 (0.298-1.661)
Antenatal care (at least 4 times)
-0.282 (0.102-0.774)*
-0.323 (0.074-1.403)
Neonatal care
-0.037 (0.005-0.285)**
-0.058 (0.013-0.253)**
Subsidized immunization
-0.067 (0.009-0.521)**
-0.000 (0.000-)
OOP Outpatient (as proportion of parental income)
0.049 (0.006-0.382)**
0.051 (0.006-0.407)**
0.163 (0.048-0.560)**
0.118 (0.031-0.444)**
OOP Inpatient (as proportion of parental income)
0.077 (0.017-0.345)**
0.078 (0.017-0.354)**
0.285 (0.119-0.684)**
0.280 (0.113-0.693)**
0-5y
Relative income
0.505 (0.334-0.765)**
0.788 (0.520-1.194)
0.551 (0.388-0.780)**
0.767 (0.541-1.089)
Antenatal care (at least 4 times)
-0.575 (0.386-0.857)**
-0.723 (0.462-1.131)
Neonatal care
-0.000 (0.000-)
-0.000 (0.000-)
Subsidized immunization
-0.167 (0.067-0.416)**
-0.075 (0.024-0.237)**
OOP Outpatient (as proportion of parental income)
0.018 (0.003-0.134)**
0.021 (0.003-0.154)**
0.031 (0.008-0.128)**
0.051 (0.013-0.207)**
OOP Inpatient (as proportion of parental income)
0.453 (0.292-0.703)**
0.581 (0.375-0.900)*
0.412 (0.272-0.622)**
0.482 (0.318-0.730)**
Model 1: adjusted for baby sex, geographical area, maternal age and maternal comorbidities, complications at birth, and health service utilization (outpatient frequency
and inpatient length)
Model 2: Model 1 + primary care use (antenatal care, neonatal care, subsidized immunization)
†: All variables dichotomized by median (high vs. low, yes vs. no)
*P<0.05; **P<0.01
25