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ORIGINAL RESEARCH |
From the Departments of Gynecology and Obstetrics and Medicine, The Johns Hopkins University School of Medicine; Departments of Health Policy and Management and Epidemiology, The Johns Hopkins School of Hygiene and Public Health; and The Welch Center for Prevention, Epidemiology and Clinical Research, The Johns Hopkins Medical Institutions, Baltimore, Maryland.
Address reprint requests to: Wanda K. Nicholson, MD, MPH, The Johns Hopkins University School of Medicine, Department of Gynecology and Obstetrics, 1000 East Eager Street, Room 3020B, Baltimore, MD 21202, E-mail: wnichol{at}jhmi.edu
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Abstract |
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 Abstract Materials and MethodsResultsDiscussionReferences |
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Methods: Maryland state hospital discharge data from 1993–1996 were used to identify hospitalizations for preterm labor without delivery and preterm labor with early delivery. Median regression was used to determine the association between patient factors and hospital care costs in Maryland and to develop a model to estimate hospital care costs nationally. National estimates of hospitalizations for preterm labor were from the 1994 National Hospital Discharge Survey.
Results: During the 4-year study period, there were 25,104 hospitalizations for preterm labor, undelivered, and preterm labor with early delivery in Maryland. Maternal comorbidity, antenatal procedures, types of insurance, and lengths of stay associated significantly with hospital costs for preterm labor. National costs for preterm labor, undelivered, were more than $360 million. Incremental costs for preterm labor with early delivery, compared with term delivery, ranged from $21 million to $191 million. Total expenditures for preterm-labor hospitalization for the United States were estimated in excess of $820 million.
Conclusion: Hospitalizations for preterm labor comprise a substantial portion of maternal cost of perinatal care in the United States. Maternal comorbidity and procedures account for major differences in costs per admission. Strategies to reduce hospitalizations for preterm labor should focus on economic and clinical outcomes in evaluating their overall values.
Obstetricians, health policy makers, and third-party payers have great interest in reducing antenatal hospitalizations for high-risk pregnancies. One of the most common reasons for antenatal hospitalizations in the United States is preterm labor and delivery, defined as labor before 37 weeks’ gestation. Data from the 1996 Pregnancy Complication Surveillance System found that preterm labor accounted for 33% of all hospitalizations before delivery in California.1 Data from the National Hospital Discharge Survey show that preterm labor can lead to multiple hospitalizations during pregnancy, maternal morbidity, and neonatal mortality.2,3
Medical interventions to reduce preterm labor and delivery have focused on different clinical pathways to preterm birth.4–7 For example, some interventions have focused on idiopathic preterm labor, whereas other interventions have focused on preterm labor preceded by premature rupture of membranes (PROM).7–10 Additional interventions have focused on prevention of preterm labor complicated by maternal disease, such as hypertension and gestational diabetes mellitus.11 Others have focused on perinatal infection as a risk for preterm labor and delivery.6,12 More recent screening tests have been developed for women with preterm labor to distinguish pregnancies at risk for imminent delivery from those less likely to progress to delivery.13–18 Although intervention studies are evaluated routinely for their impact on clinical outcomes, there is a critical need to develop a framework to evaluate their cost consequences in the current health care environment.
The first step in understanding cost consequences of preterm labor is examining the magnitude and distribution of costs and the relationship between patient factors, clinical factors, and costs. We estimated direct medical costs associated with hospitalizations for preterm labor from the perspective of society.19 Our goals were to describe the distribution and magnitude of hospital costs for preterm labor in Maryland, to determine patient and clinical factors associated with hospital costs for preterm labor in the state, and to use a model based on Maryland state data to project hospital costs for preterm labor for the United States.
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Materials and Methods |
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The data sources for this analysis were the 1993–1996 Maryland Health Services Cost Review Commission data20 and the 1994 National Hospital Discharge Survey.21 The Maryland database is publicly available and contains information on all nonfederal hospital discharges within the state of Maryland. Its information includes demographics, primary insurers, principal discharge diagnoses and up to four secondary diagnoses, principal procedures and up to four additional procedures, lengths of hospital stay, and hospital charges. Discharge diagnoses and procedures are listed as International Classification of Diseases, 9th (ICD-9) Revision codes.22 The Maryland database was used to identify hospital discharges from January 1993 to December 1996 with principal or secondary diagnoses of preterm labor, undelivered (ICD-9 code 644.00-.03), preterm labor with early delivery (ICD-9 code 644.20-.21), and normal delivery (ICD-9 code 650). The Maryland data do not link individual hospitalizations over time, so the category of normal delivery might include patients who were admitted previously for preterm labor and discharged without delivery.
The Hospital Discharge Survey is a probability sample of hospital discharges in the United States conducted annually by the National Center for Health Statistics. It collects data from approximately 270,000 inpatient records from a national sample of 500 hospitals. It contains demographics, principal insurers, discharge diagnoses and procedures, and hospital lengths of stay. It is based on a national probability sample, so the statistics from the data set are weighted national estimates. Details of data collection methods, sampling errors, and other statistical aspects of the survey are described in the Survey’s technical report.21
Independent variables included in the study and modeled as categoric variables were maternal race (white, black, other, unknown); maternal age (19 years or younger, 20–24, 25–29, 30–34, 35–39, 40 years or older); principal insurer (fee-for-service, health maintenance organization, Medicaid, Medicare, self-pay, other, or unknown); year of discharge (1993, 1994, 1995, 1996); maternal comorbidities (one or more); and obstetric procedures (one or more). Comorbidities that were listed as secondary diagnoses were reviewed for potential to affect preterm labor management and costs. They were grouped into 11 broad diagnostic categories based on similarities in clinical presentation or treatment: anemia, chorioamnionitis, diabetes mellitus, drug dependence, abnormal fetal growth, gestational diabetes mellitus, hypertensive disease, placental hemorrhage/abruption, premature rupture of membranes, pyelonephritis, and twin or triplet gestation. Multiple gestation is not a direct maternal complication but is a complicating factor in managing preterm labor. Procedures were categorized as amniocentesis, intravenous medications, ultrasound, administration of blood products, drug dependence management, other intravenous medications, maternal surgical procedures such as appendectomy, and electronic monitoring. Length of stay was treated as a continuous variable.
The primary outcome of interest was costs associated with hospital care, which included institutional and physician services. To obtain institutional cost, hospital charges were first converted to costs using hospital-specific cost-to-charge ratios obtained directly from the Maryland Health Services Cost Review Commission.23 Costs were then adjusted to 1996 dollars on the basis of the appropriate annual medical care component of the Consumer Price Index (1993 [5.9%], 1994 [4.8%], 1995 [4.5%]).24 Results are presented in constant 1996 dollars.
Costs of physician services associated with hospital care were calculated using the 1996 Medicare resource-based relative value scale.25 The number and type of hospital physician visits were for preterm labor without delivery (we assumed an initial visit, a subsequent visit for each additional hospital day, and the day of discharge), preterm labor with delivery (we assumed an initial visit, a subsequent visit for each additional hospital day, and the global fee for obstetric care, and normal delivery (we used the global fee for obstetric care). We adjusted global fees for obstetric care to reflect the increase in fees associated with cesarean delivery.
The distribution of patient characteristics in preterm labor, undelivered, and preterm labor with early delivery groups was compared using 
2 statistic for categoric variables and the t test for the continuous variable (length of stay).
Median regression was used to determine the independent effect of maternal and clinical factors on hospital care costs, while adjusting for potential confounding factors. Separate median regression models were developed for preterm labor, undelivered; preterm labor with early delivery; and term delivery. After observing a skewed frequency distribution of hospital costs, we used median regression to better account for outliers and provide more robust estimates in multivariable models. Median (quantile) regression estimates the median of the dependent variable (hospital costs) rather than the mean of the dependent variable used in linear regression.26 Covariates adjusted for in the median regression models for preterm labor without delivery were patient age, race, principal insurer, procedures, comorbidities, and hospital length of stay. In the regression models for preterm labor with early delivery and normal, term delivery, covariates outlined and mode of delivery (cesarean or vaginal) were included in the analysis. Data analysis was done using STATA 5.0 (STATA release 5, College Station, TX). P values less than .05 were considered statistically significant.
National costs for preterm labor were estimated with data from the Hospital Discharge Survey and the median regression models from the Maryland data. The sampling design of the survey was multistage, so we used STATA and sampling weights provided within the survey to make national estimates of admissions. We identified the number of admissions for preterm labor by using the appropriate ICD-9 codes. An estimate of the per-case cost for preterm labor, undelivered, was then determined by using regression coefficients from the Maryland data for categories of variables in which any of the coefficients were significant. Those variables were principal payer, comorbidity, procedures, and length of stay. The estimated per-case cost was then applied to the number of admissions for preterm labor, undelivered.
For preterm labor with early delivery, we derived an estimate of the incremental increase in costs for preterm labor with delivery relative to the costs for term delivery. We made the assumption that the increased costs for preterm labor with delivery compared with costs for term delivery was primarily caused by additional tests, procedures, and physician fees in the management of preterm labor rather than actual delivery. The per-case costs for preterm labor with early delivery were determined by using the same categories of variables outlined from regression models. The per-case costs for normal term delivery were based on significant coefficients for length of stay and payer source. The difference in the per-case costs for preterm labor with pre-term delivery and term delivery represents the incremental increase in hospital costs for preterm labor with delivery. We applied the incremental cost per case to the number of hospital cases to derive the total increase in costs for preterm labor with delivery relative to term delivery.
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Results |
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shows the distribution of maternal and clinical factors between preterm labor, undelivered, and the preterm labor with early delivery groups. The characteristics of women with normal deliveries are also listed. Maternal race, principal insurer, and number of comorbidities and procedures differed significantly between preterm labor, undelivered, and preterm labor with early delivery groups. In that analysis, 44% of hospitalizations for preterm labor, undelivered, and 47% of hospitalizations for preterm labor with early delivery were among black women. Significant differences were found in principal insurers between the preterm labor groups. There was a higher percentage of hospitalizations for pre-term labor without delivery among women with private insurance or coverage through health maintenance organizations. There was a higher percentage of hospitalizations with early delivery among women with Medicaid. Compared with the preterm labor, undelivered, group, there was a higher percentage of comorbidities and procedures in the preterm labor with early delivery group.
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). Median costs for preterm labor, undelivered, were less among women with health maintenance organizations and Medicaid compared with those with private commercial insurance. Median costs were greater for cases with one or more complications and cases with one or more procedures. Median costs were significantly less for hospitalizations in calendar years 1995 and 1996 compared with those in 1993. Table 2 also shows the median change in costs for preterm labor with delivery for maternal and clinical characteristics. Women with health maintenance organizations, Medicaid insurance, and self-pay status had lower costs compared with those with private insurance. One or more complications and one or more procedures were associated with significantly greater median costs. Black race, coverage with health maintenance organizations, self-pay status, other sources of payment, and year of hospitalization were significant factors for uncomplicated term delivery.
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outlines the number of admissions and hospital costs for preterm labor with no delivery and incremental increase in costs for preterm labor with early delivery according primary method of payment. In 1994, there were 123,715 hospitalizations for pre-term labor without delivery with a total cost in excess of $360 million. Medicaid accounted for most admissions and costs, followed by health maintenance organizations.
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Discussion |
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We found that compared with private insurance, coverage through health maintenance organizations and Medicaid associated with lower hospital costs. One or more maternal comorbid condition and maternal procedure was associated with greater median costs. Lower hospital costs with health maintenance organizations and Medicaid coverage might indicate cost containment with expansion of commercial and Medic-aid managed care in Maryland during the study period. The association of maternal comorbidity with greater costs is most likely the result of an increase in maternal and fetal surveillance based on specific maternal complication. Multiple maternal comorbid conditions could result in additional procedures and their associated costs. There was no significant association between race and cost of preterm labor per case. Total national expenditures for preterm labor exceeded $820 million and were covered primarily through Medicaid and health maintenance organizations. Those findings indicate current trends in health care, with increased coverage through health maintenance organizations and decreased coverage through traditional private insurance.
There were several limitations to this study. The analysis is based on administrative data that might have some errors in clinical coding. However, pre-term labor is a common obstetric diagnosis and would tend to be reliable.27 Many Maryland hospitals also conduct internal audits of their data before submission of data to the Health Services Cost Review Commission. It is possible that maternal complications were undercoded, which would result in an underestimate of the association between comorbidity and hospital costs. Also possible was that some normal term deliveries might have associated comorbidities that were not identifiable in the data, leading to an overestimate of incremental costs of preterm labor with delivery. Individual hospitalizations were not linked, so we were unable to estimate from the available data the costs of preterm labor hospitalizations that ultimately ended in term delivery.
Our estimates of national expenditures are based in part on Maryland data and are not necessarily generalizable to the entire United States. This analysis was limited to costs for maternal hospitalization for preterm labor and does not estimate the cost of care for preterm infants. We were unable to determine potential cost-savings and improved neonatal outcomes caused by maternal hospitalization because the Maryland data did not link maternal and infant hospitalizations. It also would have been valuable to adjust for gestational age. However, gestational age was not included in the data set. Although the costs of hospitalizations for preterm labor in the United States are large, estimation and addition of the indirect (eg, loss of wages) and direct nonmedical costs (eg, child care) would provide a more complete picture of the full costs from the perspective of society.
Despite those limitations, this study offers an important estimate of the magnitude and determinants of hospital care costs associated with preterm labor. Physicians must better understand the cost consequences of preterm labor to assess cost-effectiveness of new screening strategies and clinical management of preterm labor.
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Footnotes |
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Received November 24, 1999. Received in revised form February 3, 2000. Accepted February 17, 2000.
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References |
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20. Health Services Cost Review Commission hospital discharge data, 1993–1996.
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22. International classification of diseases—clinical modification, 9th revision. Salt Lake City: Med-Index Publications, 1993.
23. Health Services Cost Review Commission annual cost filings and approved rate orders, 1993–1996.
24. Health Care Financing Administration, OACT, Office of National Health Statistics. New York: DRI/McGraw-Hill HCC, 1995.
25. Federal register. Vol. 61, #227. November 22, 1996: 594900-59724.
26. Gould W, Rogers WH. Quantile regression as an alternative to robust regression. Proceedings of the Statistical Computing Section. American Statistical Association, 1994.
27. The Johns Hopkins Hospital report of clinical data quality review. Baltimore, MD: Deloitte, Haskins & Sells, 1998.
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