The Growing Demand for Midtrimester Amniocentesis: A Systems Approach to Forecasting the Need for Facilities HENRY F. SELLE, MED, DEBORAH W. HOLMES, PHD, AND MARY LEE INGBAR, PHD
Abstract: A predicted shift in composition of the child-bearing population of the United States to higher maternal ages by year 2000 indicates that the number of chromosomally abnormal offspring of women age 35 and over will increase by 64 per cent while the total number of women increases only 21 per cent. We formulated a conceptual model of a health care system that predicts demand for amniocentesis from prospective patients in any particular region, the number of defective offspring detected, and the future cost of custodial care using any given level of detection effort. It was found that as capacity of clinic facilities and
use by women age 35 and over in the area increased, the expenditure for amniocentesis combined with the cost of custodial care for undetected offspring decreased, assuming termination of affected pregnancies. Use of this model will enable health care managers to anticipate need for facilities, and also guide the formulation of social policy in the provision of new health services by enabling them to take into account the predictable effects of these services upon other public services. (Am. J. Public Health 69:574-580,
1979.)
Introduction The forces of supply and demand that are familiar to commerce also affect the development and availability of new medical services in the health "industry". Since such services often emerge rapidly from fundamental laboratory research, their widespread use in response to insistent public demand may tend to jeopardize both quality and accuracy. Furthermore, new medical services sometimes challenge accepted ethical positions and may call for a modification of social policy. Decisions to offer new medical services require soundly based predictions of what the public will accept and should be guided by the foreseeable effects on the need for other public services. We illustrate these considerations in this paper as they apply to midtrimester amniocentesis and the karyotyping of fetal cell cultures. We present a generic conceptual model of
Address reprint requests to Henry F. Selle, MEd, Box 852, Hanover, NH 03755. Mr. Selle is Special Consultant to Interdisciplinary Health Studies Program, Dartmouth Medical School, and Research Associate, Department of Environmental Studies, Thayer School of Engineering, Dartmouth College. Dr. Holmes is Research Associate, IHSP, Dartmouth. Dr. Ingbar is affiliated with the Department of Family and Community Medicine, University of Massachusetts Medical School, the Department of Preventive and Social Medicine, Harvard Medical School, and Beth Israel Hospital, Boston; a portion of this work was done while she was at Amos Tuck School of Business Administration, Dartmouth. This paper, submitted to the Journal July 28, 1978, was revised and accepted for publication November 15, 1978.
574
a health care system with parameters describing the service of prenatal diagnosis in the prevention of genetic disease. A systematic treatment of the relationship of capacity for service with patient demand enables potential providers of this diagnostic service to anticipate needed professional staff and equipment, as well as to estimate future charges upon society for the provision of care for genetically handicapped children. Midtrimester amniocentesis is a term that has taken on a broad meaning that includes three separate steps: genetic counseling of the patient, aspiration of amniotic fluid with the aid of ultrasonography, and the karyotyping of cultured fetal cells in the metaphase. Each of these processes has its own limits of capacity determined by the size of professional staff, available equipment, and funding resources. Two time dimensions inherent in midtrimester amniocentesis should be considered in its application as an intervention measure: * Because of the narrow gestational time limits of the 14th to 16th week within which amniotic fluid must be aspirated, the patient's request for service has an immediacy that is characteristic of treatment of acute illness. The shortrange aspect of service-on-demand indicates that peak patient loads will determine adequate size of clinic facilities, if such demand can be ascertained. * Since amniocentesis is also a disease prevention measure, it has long-range implications. The aggregate decision of those women who are screened in order to terminate abAJPH June, 1979, Vol. 69, No. 6
MIDTRIMESTER AMNIOCENTESIS: A SYSTEMS APPROACH
PERCcNT OF ALL BIRTHS
ALL ABNOMLITIES 9 8
7
3
DMiNsszE ONLY
1
-I
30
35
45 40 AGE OF MOTHER FIGURE 1-Chromosome Abnormalities as a Per Cent c[f all Births
Compared to Maternal Age SOURCE: Hook7 and Lubs'5
normal pregnancies determines the number of gene tically defective children who will become a public charge in future years. Conley and Milunsky,l updating previous work by Swanson,2 estimate that each year the births of ggenetically defective offspring in the United States create a fuiture commitment to custodial care in excess of $2 billion. AWside from the emotional burdens that a defective child bringsi to a family, these figures suggest the wisdom of increasirng present expenditures for clinical facilities to prevent the bi rths of defective children, in order to decrease future expen(ditures for their care. Thus the patient's request for service, based on pubimmediate need, is a private decision with a long-r range public impact. The correlation of Down's syndrome births w ith maternal age has been extensively documented.3-5 Reccent work by Hook and Lindsjo6 which corroborates earlierr work by Hook and Chambers7 details the rates of occurrenice by one year maternal age intervals. A similar age relaticinship appears to exist for other chromosomal errors as, well.8-'4 Lubs points out that when the mother is over 35 ye.ars of age, the proportion of chromosomal abnormalities arnong offspring rises rapidly with age to reach 10 per cent olf all births at age 45, if all types of chromosomal abnormalitiies are included'5 (Figure 1). range
AJPH June, 1979, Vol. 69, No. 6
The maternal age-risk pattern has profound implications for the health care needs of the future when it is related to a projection of population in the United States. Series II projections of the federal census'6 detailed in Table 1 forecast a 21 per cent increase in the total number of women from 1978 to 2000. But due to aging of the cohorts born during the "baby-boom" years, the number of women in the 35-44 age group is expected to increase by 75 per cent. Despite postponement in fertility and declining lifetime fertility,'7 the annual number of births occurring to the 35-44 age group is predicted to increase from 158,000 to 254,000. If the Lubs frequencies are applied to this group, 3,900 of these births in 1978 will be chromosomally abnormal. This number will increase annually to reach 6,400 abnormal births each year by the year 2000-an increase of 64 per cent in 22 years. This trend could change, if prenatal diagnosis of chromosome abnormalities and the termination of affected pregnancies were widely practiced.
Description of Model and Methods The model used in this study elaborates on the general service theory proposed by Levin and Roberts.'8 It consists of two interacting loops, or cycles, containing the elements that affect a patient's decision to request service and the clinic's decision to render that service (Figure 2). In any given population some women are aware of a need for genetic monitoring of pregnancy. The patient's decision to request service is influenced in part by counsel from her physician, her socioeconomic status, the clinic fee, insurance coverage, and ethical reservations about terminating abnormal pregnancies. After professional counseling and screening, approximately one-half of the original number of prospective patients will have the test performed, if local experience can be used as a general guide. The assurance of a normal pregnancy following diagnosis adds to public acceptance of the procedure and influences more women in the atrisk category to seek such services. Thus demand builds up. The clinic loop contains the response by health care managers to a given level of demand for service. As more women request service, the clinic is under pressure to invest TABLE 1-Population of Women in the United States, Number of Births to Women Age 35 and Over, and Number of Chromosomally Abnormal Offspring of Women Age
35 and Over Projected to Year 2000
Total number of women in the U.S. Number of women age 35-44 Annual births to women 35 + Chromosomally abnormal offspring born annually to women 35 +
1977
2000
% Increase
111,130,000
134,773,000
21
12,034,000
21,067,000
75
158,000
254,000
61
3,900
6,400
64
575
SELLE, ET AL POPULATION-AT-RISK
AWARENESS OF_ NEED ELEMENTS
PUBLIC
ACCEPTANCE
ACCEPTANCE
\
patient
PAFETIENT'
PAT IENT'tS SION
~~~~~~DECI
sec torl
QUALITY OF SERV I CE
NUMBER OF PATIENTS
~~CLINIC
interface iZnterface
cZi ni c
seator
DEMAND FOR SERVICE
CAPACITY
=
UTILIZATION FACTOR
ELEtlENTS
SUPPLY SERVICE
DCLISI O
INVESTMENT IN RESOURCES
FIGURE 2-The Health Care Model
more resources in equipment and professional staff. Thus supply of that service increases. The decision to expand is influenced in part by the cash flow from charges made for specialized equipment, repayment schedules of third party payers, public funds for expansion, the availability of qualified cytogeneticists, and the perception of socially important needs of the community served by the clinic. The number of cytogenetic diagnoses performed at the Mary Hitchcock Clinic has been increasing at an annual rate of 78 per cent since the service was started in 1972. This phenomenal increase in case load appears to be typical of a trend throughout the country. Dr. Jacobson of the President's Commission on Mental Retardation reports that the 9,900 laboratory studies of amniotic fluid performed nationwide in 1976 represent a 50 per cent increase over 1975.19 This rapid rise in demand suggests a short time delay in patient response. However, expansion of facilities involves a long time delay in procuring funding, obtaining equipment and institutional space, plus the hiring and training of professional staff. Local experience indicates a minimum 2-4 year delay between perception of need and on-line operation of a major clinical service. Such a difference in response time accounts for the dynamic behavior of a health care system and poses a management problem which will affect the quantity and quality of medical care that can be delivered at any particular time. The measurement of this difference in response time and its varying effect upon the relationship between demand for and, supply of services occurs at the interface of the two 576
cycles. This element is expressed as a fraction consisting of the number of patients seeking service divided by the number of individuals that the clinic can treat if its capacity is fully utilized; this fraction is identified as the utilization factor. The optimum condition is a factor of unity, or 1/1, indicating that all patients who request service are accommodated and that facilities are used to capacity. The underlying assumption of this analysis is that the cycles of demand for service and the supply of that service are predictable and therefore controllable, if the points of control are recognized. While public subsidy of amniocentesis and more liberal insurance benefits may tend to accelerate the demand cycle, the principal point of control in bringing supply into equilibrium with demand rests with clinic management in its decisions on investment of resources in equipment and staff. The model calculates the number of chromosomally abnormal births that are likely to occur in any particular population. It then estimates the number of such defective births that may be prevented at any given level of clinic capacity and makes a simplistic cost comparison by limiting consideration to two elements of expenditure: cost of amniocentesis with pregnancy termination, and cost of custodial care of chromosomally defective children. We are fully aware of the more extensive treatment given to the subject by other researchers.1' 3.20 Our estimates of the cost of amniocentesis with pregnancy termination are based on the following rationale: The patient is currently charged $260 for amniocentesis plus associated laboratory work and $400 for termination of pregnancy by hypertonic saline induction. The Mary Hitchcock Clinic fee of $260 was established when the service was first started in 1972 on an experimental basis. Experience since then indicates a real cost to the clinic of $350-$375 with no provision for overhead. We assume, therefore, that as capacity of service increases to 100 patients or more annually, this fee will be raised to $400 to make the service self-sustaining and to generate sufficient revenue for expansion consistent with population growth. We assume also a constant marginal cost of $400 per patient-capacity with no large front-end expansion costs. The cost figures used to reflect special care for chromosomally defective offspring are based upon maintenance costs only, exclusive of any medical or surgical service which many such handicapped individuals require. The annual charge for special care is estimated at $9,000 by reference to institutions and special care programs for the retarded in northern New England. We have followed the procedure used by Conley and Milunskyl in their measurement of costs by increasing service charges 2.5 per cent annually to reflect periodic wage increases, but without further adjustment for general inflation. The projections are presented, therefore, in 1978 dollars with the wage adjustments noted above. Since karyotyping of fetal cells at midtrimester enables the diagnosis of many chromosome abnormalities, we include all such presently identifiable defects in this analysis. The natural history and epidemiology of chromosome abnormalities other than Down's syndrome are as yet imprecisely AJPH June, 1979, Vol. 69, No. 6
MIDTRIMESTER AMNIOCENTESIS: A SYSTEMS APPROACH
defined. It was necessary, therefore, to make the following additional assumptions: * Only two-thirds of children born with chromosome abnormalities are sufficiently handicapped to require special care in an institution or in a locally administered training program. Milunsky reports in a study of 22,860 consecutively born infants'2 that structural rearrangements and autosomal aneuploidy accounted for one-half to two-thirds of significant chromosomal abnormalities, the balance consisting of sex-chromosome aneuploidy. Since most of the obviously retarded fall into the first two categories, we have used the upper bound in our assumption. * Entry into an institution was projected to occur during the first five years of life. The present trend in the care for the retarded favors locally administered training programs in the home community. But such programs which include special education and welfare support payments, which may begin at an early age, have their own high cost. Therefore, the societal cost of care, even though not specifically in a residential treatment facility, may approximate the maintenance expenditure in an institution. Furthermore, many of the severely retarded may require institutional care from birth. Therefore we believe it is reasonable to assume that public support will begin during the first five years of a retardate's life. * Chromosomally defective children will have an overall life expectancy of 20 years with an initial attrition of 25 per cent in the first year as described by Hagard and Carter.3 Conley and Milunskyl assume 20 years of institutional care (between the ages of 10 and 30) for individuals with Down's and Hunter's syndrome. Since we include chromosome abnormalities which may result in a higher incidence of neonatal death, we assume a shorter life expectancy and earlier entry into a special care facility for the group as a whole even though some individuals with Down's syndrome may live 60 years or longer.
Results The quantified version of the health care model uses population parameters that describe the sections of Vermont and New Hampshire comprising the area served by the Dartmouth Medical School and the Hitchcock clinic. Growth trends in this area indicate that the present population of 756,000 may increase to 980,000 by the end of the century. We applied the same fertility and mortality rates used in the U.S. Census, Series II projections, listed in the appendix.'7 Based on these rates we predict that births to women age 35-44 will increase annually from 559 to 1,114 during the period from 1978 to 2000. These data were inserted into the model which was then tested in three computer runs with simulations of additional assumptions that are described later.
In the absence of an intervention program the model predicts that the number of chromosomally abnormal births occurring to women age 35-44 will increase annually from 17 to 31 during the test period. Thus by the end of the century the expenditure for custodial care of chromosomally handiAJPH June, 1979, Vol. 69, No. 6
NO INTERVENTION PROGRAM
$1,500 ,000
RUN #1
RUN #2 I
RUN #3
$1,000,000 cn
a
COMPLETE
e
SCREENING
$500,000
35-44 AGE GROUP
ui
1980
85
90
95
2000
FIGURE 3-Combined Cost of Patient Screening plus Custodial Care of Genetcally Defective Children Born to Women Age 35-44 in Hitchcock Clinic Service Area between Years 1978 and 2000 at Various Levels of Clinic Capacity, Assuming That All Fetuses Diagnosed as Abnormal Are Aborted
capped children born since January 1, 1978, to women age 35-44 and surviving in the year 2000 would reach $1,502,000 each year, or a present value of cumulated future expenditures of $9,158,000 discounted at 7 per cent (Figure 3). If all pregnant women in the 35-44 age group were screened by amniocentesis and elected to terminate all chromosomally abnormal pregnancies, the cost of amniocentesis with pregnancy termination would approximate $533,000 annually by the year 2000, or a cumulated discounted expenditure of $3,446,000. However, custodial costs for care of defective offspring born to this group would be zero. These figures represent the upper and lower baselines against which the three subsequent runs of the model are measured (Table 2 and Figure 4). In the first run of the model, we exclude new equipment on order and estimate the present overall capacity of the several departments involved in cytogenetic diagnosis at 50 patients per year. As a result, demand for service, which has been increasing at an annual rate of 78 per cent, continues at an exponential rate of growth and overshoots capacity as shown by the fluctuating solid line in Run #1 of Figure 4. When more patients demand service than can be scheduled, the utilization factor becomes greater than one, which indicates an approaching crisis in quality of service. When such overcrowding occurs, the delay in appointment schedules may cause some women to miss the critical two- or three-week 577
SELLE, ET AL TABLE 2-Expenditure in the Year 2000, and Discounted Cumulated Totals, for Patient Screening and Custodial Care of Chromosomally Defective Offspring of Women Age 35 and Over Born Since 1978 and Surviving in Year 2000 In Hitchcock Clinic Service Area at Various Levels of Intervention Capacity
No intervention facilities Run #1 Run #2 Run #3 If all pregnant women age 35 and over were screened
Total Cost in Year
$ 50,000 140,500 273,800
$1,502,000 1,370,600 1,057,500 711,200
$1,502,000 1,420,600 1,198,000 985,000
$9,158,000 8,712,000
533,000
-
533,000
3,446,000
-
period during which amniotic fluid must be aspirated. Furthermore the strain of over-crowding in various departments is an open invitation to error. Any "bad press" resulting from unavailability of service and deterioration in quality of service will tend to dampen demand as shown by the collapse of the demand curve. These undesirable elements inherent in the system may, in fact, entirely destroy the utilization of this new technology. When the demand curve drops below the level of capacity, clinic schedules again open up. Demand slowly recovers to attain an equilibrium consistent with capacity. These oscillations in demand indicate inadequate capacity with the attendant danger of inferior quality. This level of service discovers no more than one to three defective pregnancies annually, or approximately 8 per cent of the total chromosomally defective pregnancies in the 3544 age group during the test period. Combined expenditures for patient diagnosis and custodial care reach $1,420,000 annually by the year 2000, or a cumulated discounted expenditure of $8,712,000. In the second run of the model, we simulated an expansion of clinic capacity to 200 patients per year and then increased this capacity at a rate consistent with population growth. As a result, demand for service closely approximates capacity of facilities indicating that all patients who request service are treated and no excess capacity exists. Annually discovered chromosomally defective pregnancies range from six to eight, or approximately 45 per cent of the total occurring in the 35-44 age group. Combined expenditures amount to $1,198,000 annually by year 2000, or a cumulated discounted expenditure of $7,254,000. We ran the model at several intermediate steps of service capacity and found that the oscillations in the demand curve indicating inferior quality did not disappear until initial capacity was increased to at least 200 patients per year. In the third run of the model, we simulated an expansion of clinic capacity to 350 patients per year and increased this 578
Discounted Cumulated Totals at 7% Years 1978 to 2000
Cost of Custodial Care for Defective Offspring in Year 2000
Cost of Patient Screening by Year 2000
2000
7,254,000 6,360,000
capacity at a rate consistent with population growth. We further simulated the effect of an education program conducted by health agencies designed to inform women in the high-risk categories of the importance of genetic counseling and prenatal cytogenetic diagnosis. As a result, latent demand is stimulated to a saturation level which is identified as the maximum response to a voluntary health program. When this level is reached, near 1995, the demand curve begins to flatten. This level, which is a parameter of the model, is set by reference to the socioeconomic status of people living in the service area and by their response in the past to publicly advocated health programs. We have estimated a peak response appropriate to our area at 60 per cent of the patients-at-risk. Annually discovered chromosomally defective pregnancies range from nine to 16, or approximately 52 per cent of the total occurring in the 3544 age group. Combined expenditures amount to $985,000 annually by year 2000, or a cumulated discounted figure of $6,360,000. It should be noted that in moving from Run #1 to Run #3 a significant shift in the burden of expense occurs from the public sector for institutional care to the private sector for amniocentesis with pregnancy termination, if elected by the patient (Table 2).
Discussion The predicted shift in the composition of the child-bearing population to higher maternal ages plus the change in lifestyle toward delayed fertility constitute a genetic "timebomb" for this country. By using the health care model presented in this paper, the health planner can estimate the number of chromosomally defective births that are likely to occur during the next 20 years in any geographical area so that remedial action can be taken to avert a possible crisis. The examples illustrate how the model may help to illuminate the complex interactions between demand for service AJPH June, 1979, Vol. 69, No. 6
MIDTRIMESTER AMNIOCENTESIS: A SYSTEMS APPROACH
DEMAND FOR SERVICE CAPACITY OF FAC I LI TI
NUMBER OF PATI ENTS
500
ES-M---
I
|RUN #1
400j
1
300 200
M
100 500
RUN #2
400 \
300 lIOC
~~~RUN #3
| 600
500
-I
the characteristics of the population-at-risk. Health planning officials characteristically define need in terms of a level of care that a given population ought to have in order to optimize health care. Such definition adds unmet need, as defined by Donabedian,2' to patients' perceived need and may result in over-expansion of facilities. The implicit assumption of Run #3 is that unmet need can be converted to active demand through an education effort which should accompany a commitment of resources to expansion. The existence of this possibility for influencing demand makes the model that has been discussed such a vital tool in the formation of public policy. The model has value in anticipating how programs designed to expand demand should be correlated with those designed to influence the availability of facilities. Thus, services required to meet desired demand can be developed and the provision of health services can be regionalized at more optimum levels from the point of view of the health status of the population to be served. A number of recent articles have referred to a major growth in the demand for amniocentesis services.23-25 We are fully aware that the simulated condition of complete screening of all pregnant women age 35 and over cannot be met in a free society based on differing ethical concepts. However, general debate on the issues raised by amniocentesis, as advocated by Etzioni,26 may strike a balance between economics and freedom of choice and ultimately lead to a decision on the appropriate expenditure of public funds.
I
'.
1-~I
REFERENCES 1. Conley RC, Milunsky A: Economics of prenatal genetic diagno-
300
llll
2. 3.
i
100
1980
1990
4.
2000
FIGURE 4-Three Runs of the Health Care Model Projected to Year 2000
and the availability of resources to meet this demand. It is important to note that need is defined in the model from the patient's perspective, as discussed by Donabedian.2' This perspective results in a calculation of demand that conforms to the market signal approach advocated by Newhouse.22 A high use ratio is likely to occur when facilities are built in response to this concept of patients' need. Under these conditions one may question whether the existing level of demand is appropriate, given the current state of medical knowledge, the safety of the procedure, and AJPH June, 1979, Vol. 69, No. 6
5.
6.
7.
8. 9.
sis in Prevention of genetic disease and mental retardation, edited by A Milunsky, W. B. Saunders Co., Philadelphia, 1975. Swanson TE: Economics of mongolism. Ann NY Acad Sci, 171:679, 1971. Hagard S, Carter FA: Preventing the birth of infants with Down's syndrome: A cost-benefit analysis. Br Med J 1(6012):753-6, March 27, 1976. Ferguson-Smith MA: Letter: Prospective data on risk of Down syndrome in relation to maternal age. Lancet 2(7979):252, July 31, 1976. Hook EB: Estimates of maternal age-specific risks of Downsyndrome birth in women aged 34-41. Lancet 2(7975):33-4, July 3, 1976. Hook EB, Lindsjo A: Down's syndrome in live births by single year maternal age interval in a Swedish study: Comparison of results from a New York State study. Am J Hum Genet 30:1927, 1978. Hook EB, Chambers JE: Estimated rates of Down syndrome in live births by one year maternal age intervals for mothers aged 20-49 in a New York state study-implications of the risk figures for genetic counseling and cost-benefit analysis of prenatal diagnosis programs. Birth Defects: Original article series 13:123-141, 1977. Lubs HA, Ruddle FH: Chromosomal abnormalities in the human population: Estimation of rates based on New Haven newborn study. Science 169:495-7, July 31, 1970. Lubs HA, Lubs ML: Genetic disorders. in Medical complications during pregnancy. Edited by GN Burrow and TF Ferris, Philadelphia, W. B. Saunders Co., 1975. 579
SELLE, ET AL 10. Lewandowski RC Jr, Yunis JJ: New chromosomal syndromes. Am J Dis Child 129(4):515-29, Apr 1975. 11. Milunsky A: Current concepts in genetics: prental diagnosis of genetic disorders. N Engl J Med 295(7):377-80, August 12, 1976. 12. Milunsky A: Prevention of genetic disease and mental retardation. Philadelphia, W. B. Saunders Co., 1975. 13. Hamerton JL, Canning N, Ray M: A cytogenetic survey of 14,069 newborn infants: Incidence of chromosome abnormalities. Clin Genet 8:223, 1975. 14. Milunsky A, Atkins L: Prenatal diagnosis of genetic disorders: An analysis of experience with 600 cases. JAMA 230(2):232-5, October 14, 1974. 15. Lubs HA: The current state of the art. Workshop on automated cytogenetics, Pacific Grove, Calif, 1975. In Automation of cytogenetics: Asilomar Workshop, Pacific Grove, California, Nov 30-Dec 2, 1975, edited by ML Mendelsohn. Alexandria, Va., National Technical Information Service, 1976. pp 174-177. 16. United States Bureau of the Census. Current Population Reports: Series P-25, Population estimates and projections. No. 601, Projections of the population of the United States: 1975 to 2050. Washington, D.C., Government Printing Office, 1975. Table 8, Series II, pp. 67-92. 17. ibid. Table A-5, p. 126; Table B-4, p. 133; Table D-4 and D-5, p. 137. 18. Levin G, Roberts EB: The dynamics of human service delivery. Cambridge, Ballinger Press, Inc., 1976. p. 17-24. 19. Amniocentesis use on rise. President's Commission on Mental Retardation Newsletter, #44, October 1976. 20. Conley R: The economics of mental retardation. Baltimore, Johns Hopkins Press, 1973. 21. Donabedian A: Aspects of medical care administration. Cambridge, Harvard Press, 1973. p. 62-8. 22. Newhouse JP: Forecasting demand and the planning of health services in Systems aspects of health planning: proceedings of the International Institute of Applied Systems Analysis Conference, Laxenburg, Austria, 1974, edited by NTJ Bailey and M Thompson. Amsterdam, North-Holland Pub. Co., 1975. 23. Mennuti MT: Prenatal genetic diagnosis: Current status. N Engl J Med 297:1004-6, November 3, 1977. 24. Omenn GS: Prenatal diagnosis of genetic disorders. Science 200:952-8, May 26, 1978. 25. Epstein CJ, Golbus MS: Prenatal diagnosis of genetic diseases. Am Scientist 65(6): 703-11, November 1977. 26. Etzioni A: Issues of public policy in the USA raised by amniocentesis. J. Med Ethics 2(1):8-11, March 1976.
580
ACKNOWLEDGMENTS Supported in part by a grant from the Public Affairs Center of Dartmouth College from funds contributed by the Spaulding-Potter Trust. We are indebted to Dr. Thomas P. Almy for advice and general review, to Professor Dennis L. Meadows for assistance in system programming, and to Dr. Doris Wurster-Hill for guidance through the intricacies of cytogenetics.
APPENDIX Principal Variables Used in the Health Care Model Exogenous variables 1960-1970 U.S. Census by 5-year cohorts Series II projected fertility and mortality rates17 Local fees for clinic and institutional care
Frequencies of occurrence of chromosomal abnormalities by maternal age's Clinic capacity (local experience) Clinic expansion delays (local experience) Maximum response to voluntary health care program (local experience) Endogenous variables Number of women-at-risk by cohort Number of defective births Number of defective births averted Number of actual patients Rate of expansion of clinic capacity Availability of service and quality of service Public demand for service U.S. Census Series II Fertility Rates'7
Year 1977 2000
Live births per 1000 Age Age 40-44 35-39 20.5 5.1 4.7 19.6
AJPH June, 1979, Vol. 69, No. 6
Abstract: A predicted shift in composition of the child-bearing population of the United States to higher maternal ages by year 2000 indicates that the number of chromosomally abnormal offspring of women age 35 and over will increase by 64 per cent while the total number of women increases only 21 per cent. We formulated a conceptual model of a health care system that predicts demand for amniocentesis from prospective patients in any particular region, the number of defective offspring detected, and the future cost of custodial care using any given level of detection effort. It was found that as capacity of clinic facilities and
use by women age 35 and over in the area increased, the expenditure for amniocentesis combined with the cost of custodial care for undetected offspring decreased, assuming termination of affected pregnancies. Use of this model will enable health care managers to anticipate need for facilities, and also guide the formulation of social policy in the provision of new health services by enabling them to take into account the predictable effects of these services upon other public services. (Am. J. Public Health 69:574-580,
1979.)
Introduction The forces of supply and demand that are familiar to commerce also affect the development and availability of new medical services in the health "industry". Since such services often emerge rapidly from fundamental laboratory research, their widespread use in response to insistent public demand may tend to jeopardize both quality and accuracy. Furthermore, new medical services sometimes challenge accepted ethical positions and may call for a modification of social policy. Decisions to offer new medical services require soundly based predictions of what the public will accept and should be guided by the foreseeable effects on the need for other public services. We illustrate these considerations in this paper as they apply to midtrimester amniocentesis and the karyotyping of fetal cell cultures. We present a generic conceptual model of
Address reprint requests to Henry F. Selle, MEd, Box 852, Hanover, NH 03755. Mr. Selle is Special Consultant to Interdisciplinary Health Studies Program, Dartmouth Medical School, and Research Associate, Department of Environmental Studies, Thayer School of Engineering, Dartmouth College. Dr. Holmes is Research Associate, IHSP, Dartmouth. Dr. Ingbar is affiliated with the Department of Family and Community Medicine, University of Massachusetts Medical School, the Department of Preventive and Social Medicine, Harvard Medical School, and Beth Israel Hospital, Boston; a portion of this work was done while she was at Amos Tuck School of Business Administration, Dartmouth. This paper, submitted to the Journal July 28, 1978, was revised and accepted for publication November 15, 1978.
574
a health care system with parameters describing the service of prenatal diagnosis in the prevention of genetic disease. A systematic treatment of the relationship of capacity for service with patient demand enables potential providers of this diagnostic service to anticipate needed professional staff and equipment, as well as to estimate future charges upon society for the provision of care for genetically handicapped children. Midtrimester amniocentesis is a term that has taken on a broad meaning that includes three separate steps: genetic counseling of the patient, aspiration of amniotic fluid with the aid of ultrasonography, and the karyotyping of cultured fetal cells in the metaphase. Each of these processes has its own limits of capacity determined by the size of professional staff, available equipment, and funding resources. Two time dimensions inherent in midtrimester amniocentesis should be considered in its application as an intervention measure: * Because of the narrow gestational time limits of the 14th to 16th week within which amniotic fluid must be aspirated, the patient's request for service has an immediacy that is characteristic of treatment of acute illness. The shortrange aspect of service-on-demand indicates that peak patient loads will determine adequate size of clinic facilities, if such demand can be ascertained. * Since amniocentesis is also a disease prevention measure, it has long-range implications. The aggregate decision of those women who are screened in order to terminate abAJPH June, 1979, Vol. 69, No. 6
MIDTRIMESTER AMNIOCENTESIS: A SYSTEMS APPROACH
PERCcNT OF ALL BIRTHS
ALL ABNOMLITIES 9 8
7
3
DMiNsszE ONLY
1
-I
30
35
45 40 AGE OF MOTHER FIGURE 1-Chromosome Abnormalities as a Per Cent c[f all Births
Compared to Maternal Age SOURCE: Hook7 and Lubs'5
normal pregnancies determines the number of gene tically defective children who will become a public charge in future years. Conley and Milunsky,l updating previous work by Swanson,2 estimate that each year the births of ggenetically defective offspring in the United States create a fuiture commitment to custodial care in excess of $2 billion. AWside from the emotional burdens that a defective child bringsi to a family, these figures suggest the wisdom of increasirng present expenditures for clinical facilities to prevent the bi rths of defective children, in order to decrease future expen(ditures for their care. Thus the patient's request for service, based on pubimmediate need, is a private decision with a long-r range public impact. The correlation of Down's syndrome births w ith maternal age has been extensively documented.3-5 Reccent work by Hook and Lindsjo6 which corroborates earlierr work by Hook and Chambers7 details the rates of occurrenice by one year maternal age intervals. A similar age relaticinship appears to exist for other chromosomal errors as, well.8-'4 Lubs points out that when the mother is over 35 ye.ars of age, the proportion of chromosomal abnormalities arnong offspring rises rapidly with age to reach 10 per cent olf all births at age 45, if all types of chromosomal abnormalitiies are included'5 (Figure 1). range
AJPH June, 1979, Vol. 69, No. 6
The maternal age-risk pattern has profound implications for the health care needs of the future when it is related to a projection of population in the United States. Series II projections of the federal census'6 detailed in Table 1 forecast a 21 per cent increase in the total number of women from 1978 to 2000. But due to aging of the cohorts born during the "baby-boom" years, the number of women in the 35-44 age group is expected to increase by 75 per cent. Despite postponement in fertility and declining lifetime fertility,'7 the annual number of births occurring to the 35-44 age group is predicted to increase from 158,000 to 254,000. If the Lubs frequencies are applied to this group, 3,900 of these births in 1978 will be chromosomally abnormal. This number will increase annually to reach 6,400 abnormal births each year by the year 2000-an increase of 64 per cent in 22 years. This trend could change, if prenatal diagnosis of chromosome abnormalities and the termination of affected pregnancies were widely practiced.
Description of Model and Methods The model used in this study elaborates on the general service theory proposed by Levin and Roberts.'8 It consists of two interacting loops, or cycles, containing the elements that affect a patient's decision to request service and the clinic's decision to render that service (Figure 2). In any given population some women are aware of a need for genetic monitoring of pregnancy. The patient's decision to request service is influenced in part by counsel from her physician, her socioeconomic status, the clinic fee, insurance coverage, and ethical reservations about terminating abnormal pregnancies. After professional counseling and screening, approximately one-half of the original number of prospective patients will have the test performed, if local experience can be used as a general guide. The assurance of a normal pregnancy following diagnosis adds to public acceptance of the procedure and influences more women in the atrisk category to seek such services. Thus demand builds up. The clinic loop contains the response by health care managers to a given level of demand for service. As more women request service, the clinic is under pressure to invest TABLE 1-Population of Women in the United States, Number of Births to Women Age 35 and Over, and Number of Chromosomally Abnormal Offspring of Women Age
35 and Over Projected to Year 2000
Total number of women in the U.S. Number of women age 35-44 Annual births to women 35 + Chromosomally abnormal offspring born annually to women 35 +
1977
2000
% Increase
111,130,000
134,773,000
21
12,034,000
21,067,000
75
158,000
254,000
61
3,900
6,400
64
575
SELLE, ET AL POPULATION-AT-RISK
AWARENESS OF_ NEED ELEMENTS
PUBLIC
ACCEPTANCE
ACCEPTANCE
\
patient
PAFETIENT'
PAT IENT'tS SION
~~~~~~DECI
sec torl
QUALITY OF SERV I CE
NUMBER OF PATIENTS
~~CLINIC
interface iZnterface
cZi ni c
seator
DEMAND FOR SERVICE
CAPACITY
=
UTILIZATION FACTOR
ELEtlENTS
SUPPLY SERVICE
DCLISI O
INVESTMENT IN RESOURCES
FIGURE 2-The Health Care Model
more resources in equipment and professional staff. Thus supply of that service increases. The decision to expand is influenced in part by the cash flow from charges made for specialized equipment, repayment schedules of third party payers, public funds for expansion, the availability of qualified cytogeneticists, and the perception of socially important needs of the community served by the clinic. The number of cytogenetic diagnoses performed at the Mary Hitchcock Clinic has been increasing at an annual rate of 78 per cent since the service was started in 1972. This phenomenal increase in case load appears to be typical of a trend throughout the country. Dr. Jacobson of the President's Commission on Mental Retardation reports that the 9,900 laboratory studies of amniotic fluid performed nationwide in 1976 represent a 50 per cent increase over 1975.19 This rapid rise in demand suggests a short time delay in patient response. However, expansion of facilities involves a long time delay in procuring funding, obtaining equipment and institutional space, plus the hiring and training of professional staff. Local experience indicates a minimum 2-4 year delay between perception of need and on-line operation of a major clinical service. Such a difference in response time accounts for the dynamic behavior of a health care system and poses a management problem which will affect the quantity and quality of medical care that can be delivered at any particular time. The measurement of this difference in response time and its varying effect upon the relationship between demand for and, supply of services occurs at the interface of the two 576
cycles. This element is expressed as a fraction consisting of the number of patients seeking service divided by the number of individuals that the clinic can treat if its capacity is fully utilized; this fraction is identified as the utilization factor. The optimum condition is a factor of unity, or 1/1, indicating that all patients who request service are accommodated and that facilities are used to capacity. The underlying assumption of this analysis is that the cycles of demand for service and the supply of that service are predictable and therefore controllable, if the points of control are recognized. While public subsidy of amniocentesis and more liberal insurance benefits may tend to accelerate the demand cycle, the principal point of control in bringing supply into equilibrium with demand rests with clinic management in its decisions on investment of resources in equipment and staff. The model calculates the number of chromosomally abnormal births that are likely to occur in any particular population. It then estimates the number of such defective births that may be prevented at any given level of clinic capacity and makes a simplistic cost comparison by limiting consideration to two elements of expenditure: cost of amniocentesis with pregnancy termination, and cost of custodial care of chromosomally defective children. We are fully aware of the more extensive treatment given to the subject by other researchers.1' 3.20 Our estimates of the cost of amniocentesis with pregnancy termination are based on the following rationale: The patient is currently charged $260 for amniocentesis plus associated laboratory work and $400 for termination of pregnancy by hypertonic saline induction. The Mary Hitchcock Clinic fee of $260 was established when the service was first started in 1972 on an experimental basis. Experience since then indicates a real cost to the clinic of $350-$375 with no provision for overhead. We assume, therefore, that as capacity of service increases to 100 patients or more annually, this fee will be raised to $400 to make the service self-sustaining and to generate sufficient revenue for expansion consistent with population growth. We assume also a constant marginal cost of $400 per patient-capacity with no large front-end expansion costs. The cost figures used to reflect special care for chromosomally defective offspring are based upon maintenance costs only, exclusive of any medical or surgical service which many such handicapped individuals require. The annual charge for special care is estimated at $9,000 by reference to institutions and special care programs for the retarded in northern New England. We have followed the procedure used by Conley and Milunskyl in their measurement of costs by increasing service charges 2.5 per cent annually to reflect periodic wage increases, but without further adjustment for general inflation. The projections are presented, therefore, in 1978 dollars with the wage adjustments noted above. Since karyotyping of fetal cells at midtrimester enables the diagnosis of many chromosome abnormalities, we include all such presently identifiable defects in this analysis. The natural history and epidemiology of chromosome abnormalities other than Down's syndrome are as yet imprecisely AJPH June, 1979, Vol. 69, No. 6
MIDTRIMESTER AMNIOCENTESIS: A SYSTEMS APPROACH
defined. It was necessary, therefore, to make the following additional assumptions: * Only two-thirds of children born with chromosome abnormalities are sufficiently handicapped to require special care in an institution or in a locally administered training program. Milunsky reports in a study of 22,860 consecutively born infants'2 that structural rearrangements and autosomal aneuploidy accounted for one-half to two-thirds of significant chromosomal abnormalities, the balance consisting of sex-chromosome aneuploidy. Since most of the obviously retarded fall into the first two categories, we have used the upper bound in our assumption. * Entry into an institution was projected to occur during the first five years of life. The present trend in the care for the retarded favors locally administered training programs in the home community. But such programs which include special education and welfare support payments, which may begin at an early age, have their own high cost. Therefore, the societal cost of care, even though not specifically in a residential treatment facility, may approximate the maintenance expenditure in an institution. Furthermore, many of the severely retarded may require institutional care from birth. Therefore we believe it is reasonable to assume that public support will begin during the first five years of a retardate's life. * Chromosomally defective children will have an overall life expectancy of 20 years with an initial attrition of 25 per cent in the first year as described by Hagard and Carter.3 Conley and Milunskyl assume 20 years of institutional care (between the ages of 10 and 30) for individuals with Down's and Hunter's syndrome. Since we include chromosome abnormalities which may result in a higher incidence of neonatal death, we assume a shorter life expectancy and earlier entry into a special care facility for the group as a whole even though some individuals with Down's syndrome may live 60 years or longer.
Results The quantified version of the health care model uses population parameters that describe the sections of Vermont and New Hampshire comprising the area served by the Dartmouth Medical School and the Hitchcock clinic. Growth trends in this area indicate that the present population of 756,000 may increase to 980,000 by the end of the century. We applied the same fertility and mortality rates used in the U.S. Census, Series II projections, listed in the appendix.'7 Based on these rates we predict that births to women age 35-44 will increase annually from 559 to 1,114 during the period from 1978 to 2000. These data were inserted into the model which was then tested in three computer runs with simulations of additional assumptions that are described later.
In the absence of an intervention program the model predicts that the number of chromosomally abnormal births occurring to women age 35-44 will increase annually from 17 to 31 during the test period. Thus by the end of the century the expenditure for custodial care of chromosomally handiAJPH June, 1979, Vol. 69, No. 6
NO INTERVENTION PROGRAM
$1,500 ,000
RUN #1
RUN #2 I
RUN #3
$1,000,000 cn
a
COMPLETE
e
SCREENING
$500,000
35-44 AGE GROUP
ui
1980
85
90
95
2000
FIGURE 3-Combined Cost of Patient Screening plus Custodial Care of Genetcally Defective Children Born to Women Age 35-44 in Hitchcock Clinic Service Area between Years 1978 and 2000 at Various Levels of Clinic Capacity, Assuming That All Fetuses Diagnosed as Abnormal Are Aborted
capped children born since January 1, 1978, to women age 35-44 and surviving in the year 2000 would reach $1,502,000 each year, or a present value of cumulated future expenditures of $9,158,000 discounted at 7 per cent (Figure 3). If all pregnant women in the 35-44 age group were screened by amniocentesis and elected to terminate all chromosomally abnormal pregnancies, the cost of amniocentesis with pregnancy termination would approximate $533,000 annually by the year 2000, or a cumulated discounted expenditure of $3,446,000. However, custodial costs for care of defective offspring born to this group would be zero. These figures represent the upper and lower baselines against which the three subsequent runs of the model are measured (Table 2 and Figure 4). In the first run of the model, we exclude new equipment on order and estimate the present overall capacity of the several departments involved in cytogenetic diagnosis at 50 patients per year. As a result, demand for service, which has been increasing at an annual rate of 78 per cent, continues at an exponential rate of growth and overshoots capacity as shown by the fluctuating solid line in Run #1 of Figure 4. When more patients demand service than can be scheduled, the utilization factor becomes greater than one, which indicates an approaching crisis in quality of service. When such overcrowding occurs, the delay in appointment schedules may cause some women to miss the critical two- or three-week 577
SELLE, ET AL TABLE 2-Expenditure in the Year 2000, and Discounted Cumulated Totals, for Patient Screening and Custodial Care of Chromosomally Defective Offspring of Women Age 35 and Over Born Since 1978 and Surviving in Year 2000 In Hitchcock Clinic Service Area at Various Levels of Intervention Capacity
No intervention facilities Run #1 Run #2 Run #3 If all pregnant women age 35 and over were screened
Total Cost in Year
$ 50,000 140,500 273,800
$1,502,000 1,370,600 1,057,500 711,200
$1,502,000 1,420,600 1,198,000 985,000
$9,158,000 8,712,000
533,000
-
533,000
3,446,000
-
period during which amniotic fluid must be aspirated. Furthermore the strain of over-crowding in various departments is an open invitation to error. Any "bad press" resulting from unavailability of service and deterioration in quality of service will tend to dampen demand as shown by the collapse of the demand curve. These undesirable elements inherent in the system may, in fact, entirely destroy the utilization of this new technology. When the demand curve drops below the level of capacity, clinic schedules again open up. Demand slowly recovers to attain an equilibrium consistent with capacity. These oscillations in demand indicate inadequate capacity with the attendant danger of inferior quality. This level of service discovers no more than one to three defective pregnancies annually, or approximately 8 per cent of the total chromosomally defective pregnancies in the 3544 age group during the test period. Combined expenditures for patient diagnosis and custodial care reach $1,420,000 annually by the year 2000, or a cumulated discounted expenditure of $8,712,000. In the second run of the model, we simulated an expansion of clinic capacity to 200 patients per year and then increased this capacity at a rate consistent with population growth. As a result, demand for service closely approximates capacity of facilities indicating that all patients who request service are treated and no excess capacity exists. Annually discovered chromosomally defective pregnancies range from six to eight, or approximately 45 per cent of the total occurring in the 35-44 age group. Combined expenditures amount to $1,198,000 annually by year 2000, or a cumulated discounted expenditure of $7,254,000. We ran the model at several intermediate steps of service capacity and found that the oscillations in the demand curve indicating inferior quality did not disappear until initial capacity was increased to at least 200 patients per year. In the third run of the model, we simulated an expansion of clinic capacity to 350 patients per year and increased this 578
Discounted Cumulated Totals at 7% Years 1978 to 2000
Cost of Custodial Care for Defective Offspring in Year 2000
Cost of Patient Screening by Year 2000
2000
7,254,000 6,360,000
capacity at a rate consistent with population growth. We further simulated the effect of an education program conducted by health agencies designed to inform women in the high-risk categories of the importance of genetic counseling and prenatal cytogenetic diagnosis. As a result, latent demand is stimulated to a saturation level which is identified as the maximum response to a voluntary health program. When this level is reached, near 1995, the demand curve begins to flatten. This level, which is a parameter of the model, is set by reference to the socioeconomic status of people living in the service area and by their response in the past to publicly advocated health programs. We have estimated a peak response appropriate to our area at 60 per cent of the patients-at-risk. Annually discovered chromosomally defective pregnancies range from nine to 16, or approximately 52 per cent of the total occurring in the 3544 age group. Combined expenditures amount to $985,000 annually by year 2000, or a cumulated discounted figure of $6,360,000. It should be noted that in moving from Run #1 to Run #3 a significant shift in the burden of expense occurs from the public sector for institutional care to the private sector for amniocentesis with pregnancy termination, if elected by the patient (Table 2).
Discussion The predicted shift in the composition of the child-bearing population to higher maternal ages plus the change in lifestyle toward delayed fertility constitute a genetic "timebomb" for this country. By using the health care model presented in this paper, the health planner can estimate the number of chromosomally defective births that are likely to occur during the next 20 years in any geographical area so that remedial action can be taken to avert a possible crisis. The examples illustrate how the model may help to illuminate the complex interactions between demand for service AJPH June, 1979, Vol. 69, No. 6
MIDTRIMESTER AMNIOCENTESIS: A SYSTEMS APPROACH
DEMAND FOR SERVICE CAPACITY OF FAC I LI TI
NUMBER OF PATI ENTS
500
ES-M---
I
|RUN #1
400j
1
300 200
M
100 500
RUN #2
400 \
300 lIOC
~~~RUN #3
| 600
500
-I
the characteristics of the population-at-risk. Health planning officials characteristically define need in terms of a level of care that a given population ought to have in order to optimize health care. Such definition adds unmet need, as defined by Donabedian,2' to patients' perceived need and may result in over-expansion of facilities. The implicit assumption of Run #3 is that unmet need can be converted to active demand through an education effort which should accompany a commitment of resources to expansion. The existence of this possibility for influencing demand makes the model that has been discussed such a vital tool in the formation of public policy. The model has value in anticipating how programs designed to expand demand should be correlated with those designed to influence the availability of facilities. Thus, services required to meet desired demand can be developed and the provision of health services can be regionalized at more optimum levels from the point of view of the health status of the population to be served. A number of recent articles have referred to a major growth in the demand for amniocentesis services.23-25 We are fully aware that the simulated condition of complete screening of all pregnant women age 35 and over cannot be met in a free society based on differing ethical concepts. However, general debate on the issues raised by amniocentesis, as advocated by Etzioni,26 may strike a balance between economics and freedom of choice and ultimately lead to a decision on the appropriate expenditure of public funds.
I
'.
1-~I
REFERENCES 1. Conley RC, Milunsky A: Economics of prenatal genetic diagno-
300
llll
2. 3.
i
100
1980
1990
4.
2000
FIGURE 4-Three Runs of the Health Care Model Projected to Year 2000
and the availability of resources to meet this demand. It is important to note that need is defined in the model from the patient's perspective, as discussed by Donabedian.2' This perspective results in a calculation of demand that conforms to the market signal approach advocated by Newhouse.22 A high use ratio is likely to occur when facilities are built in response to this concept of patients' need. Under these conditions one may question whether the existing level of demand is appropriate, given the current state of medical knowledge, the safety of the procedure, and AJPH June, 1979, Vol. 69, No. 6
5.
6.
7.
8. 9.
sis in Prevention of genetic disease and mental retardation, edited by A Milunsky, W. B. Saunders Co., Philadelphia, 1975. Swanson TE: Economics of mongolism. Ann NY Acad Sci, 171:679, 1971. Hagard S, Carter FA: Preventing the birth of infants with Down's syndrome: A cost-benefit analysis. Br Med J 1(6012):753-6, March 27, 1976. Ferguson-Smith MA: Letter: Prospective data on risk of Down syndrome in relation to maternal age. Lancet 2(7979):252, July 31, 1976. Hook EB: Estimates of maternal age-specific risks of Downsyndrome birth in women aged 34-41. Lancet 2(7975):33-4, July 3, 1976. Hook EB, Lindsjo A: Down's syndrome in live births by single year maternal age interval in a Swedish study: Comparison of results from a New York State study. Am J Hum Genet 30:1927, 1978. Hook EB, Chambers JE: Estimated rates of Down syndrome in live births by one year maternal age intervals for mothers aged 20-49 in a New York state study-implications of the risk figures for genetic counseling and cost-benefit analysis of prenatal diagnosis programs. Birth Defects: Original article series 13:123-141, 1977. Lubs HA, Ruddle FH: Chromosomal abnormalities in the human population: Estimation of rates based on New Haven newborn study. Science 169:495-7, July 31, 1970. Lubs HA, Lubs ML: Genetic disorders. in Medical complications during pregnancy. Edited by GN Burrow and TF Ferris, Philadelphia, W. B. Saunders Co., 1975. 579
SELLE, ET AL 10. Lewandowski RC Jr, Yunis JJ: New chromosomal syndromes. Am J Dis Child 129(4):515-29, Apr 1975. 11. Milunsky A: Current concepts in genetics: prental diagnosis of genetic disorders. N Engl J Med 295(7):377-80, August 12, 1976. 12. Milunsky A: Prevention of genetic disease and mental retardation. Philadelphia, W. B. Saunders Co., 1975. 13. Hamerton JL, Canning N, Ray M: A cytogenetic survey of 14,069 newborn infants: Incidence of chromosome abnormalities. Clin Genet 8:223, 1975. 14. Milunsky A, Atkins L: Prenatal diagnosis of genetic disorders: An analysis of experience with 600 cases. JAMA 230(2):232-5, October 14, 1974. 15. Lubs HA: The current state of the art. Workshop on automated cytogenetics, Pacific Grove, Calif, 1975. In Automation of cytogenetics: Asilomar Workshop, Pacific Grove, California, Nov 30-Dec 2, 1975, edited by ML Mendelsohn. Alexandria, Va., National Technical Information Service, 1976. pp 174-177. 16. United States Bureau of the Census. Current Population Reports: Series P-25, Population estimates and projections. No. 601, Projections of the population of the United States: 1975 to 2050. Washington, D.C., Government Printing Office, 1975. Table 8, Series II, pp. 67-92. 17. ibid. Table A-5, p. 126; Table B-4, p. 133; Table D-4 and D-5, p. 137. 18. Levin G, Roberts EB: The dynamics of human service delivery. Cambridge, Ballinger Press, Inc., 1976. p. 17-24. 19. Amniocentesis use on rise. President's Commission on Mental Retardation Newsletter, #44, October 1976. 20. Conley R: The economics of mental retardation. Baltimore, Johns Hopkins Press, 1973. 21. Donabedian A: Aspects of medical care administration. Cambridge, Harvard Press, 1973. p. 62-8. 22. Newhouse JP: Forecasting demand and the planning of health services in Systems aspects of health planning: proceedings of the International Institute of Applied Systems Analysis Conference, Laxenburg, Austria, 1974, edited by NTJ Bailey and M Thompson. Amsterdam, North-Holland Pub. Co., 1975. 23. Mennuti MT: Prenatal genetic diagnosis: Current status. N Engl J Med 297:1004-6, November 3, 1977. 24. Omenn GS: Prenatal diagnosis of genetic disorders. Science 200:952-8, May 26, 1978. 25. Epstein CJ, Golbus MS: Prenatal diagnosis of genetic diseases. Am Scientist 65(6): 703-11, November 1977. 26. Etzioni A: Issues of public policy in the USA raised by amniocentesis. J. Med Ethics 2(1):8-11, March 1976.
580
ACKNOWLEDGMENTS Supported in part by a grant from the Public Affairs Center of Dartmouth College from funds contributed by the Spaulding-Potter Trust. We are indebted to Dr. Thomas P. Almy for advice and general review, to Professor Dennis L. Meadows for assistance in system programming, and to Dr. Doris Wurster-Hill for guidance through the intricacies of cytogenetics.
APPENDIX Principal Variables Used in the Health Care Model Exogenous variables 1960-1970 U.S. Census by 5-year cohorts Series II projected fertility and mortality rates17 Local fees for clinic and institutional care
Frequencies of occurrence of chromosomal abnormalities by maternal age's Clinic capacity (local experience) Clinic expansion delays (local experience) Maximum response to voluntary health care program (local experience) Endogenous variables Number of women-at-risk by cohort Number of defective births Number of defective births averted Number of actual patients Rate of expansion of clinic capacity Availability of service and quality of service Public demand for service U.S. Census Series II Fertility Rates'7
Year 1977 2000
Live births per 1000 Age Age 40-44 35-39 20.5 5.1 4.7 19.6
AJPH June, 1979, Vol. 69, No. 6
