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Surveillance for Anencephaly and Spina Bifida and the Impact of Prenatal Diagnosis -- United States, 1985-1994

Janet D. Cragan, M.D. Helen E. Roberts, M.D. Larry D. Edmonds, M.S.P.H. Muin J. Khoury, M.D., Ph.D. Division of Birth Defects and Developmental Disabilities National Center for Environmental Health

Russell S. Kirby, Ph.D., M.S. Arkansas Reproductive Health Monitoring System

Gary M. Shaw, Dr.P.H. Ellen M. Velie, M.P.H. California Birth Defects Monitoring Program

Ruth D. Merz, M.S. Mathias B. Forrester, B.S. Hawaii Birth Defects Monitoring Program

Roger A. Williamson, M.D. Diane S. Krishnamurti, M.S. Iowa Birth Defects Registry and the University of Iowa

Roger E. Stevenson, M.D. Jane H. Dean, R.N. Greenwood Genetic Center

Abstract

Problem/Condition: The reported prevalence of anencephaly and spina bifida in the United States has steadily declined since the late 1960s. During this time, the ability to diagnose these defects prenatally has progressed rapidly. Many U.S. birth defects surveillance systems ascertain defects only among live-born infants or among infants and fetuses beyond a certain gestational age, thus excluding defects among pregnancies prenatally diagnosed as being affected by a neural tube defect (NTD) and electively terminated before the gestational age limit. The impact of prenatal diagnosis and subsequent pregnancy termination on the reported prevalence of anencephaly and spina bifida in the United States has not been well established. However, assessment of this impact is crucial to the use of surveillance data to monitor trends in the occurrence of NTDs and the effectiveness of interventions for these defects (e.g., increased consumption of folic acid).

Reporting Period: This report presents data from birth defects surveillance systems in six states over different time periods: Arkansas, 1985-1989; California, 1989-1991; Georgia, 1990-1991; Hawaii, 1988-1994; Iowa, 1985-1990; and South Carolina, 1992-1993.

Description of Systems: Population-based data about a) live-born and stillborn infants with anencephaly and spina bifida and b) pregnancies electively terminated after prenatal diagnosis of these defects were analyzed from the Arkansas Reproductive Health Monitoring System; the California Birth Defects Monitoring Program; CDC's Metropolitan Atlanta Congenital Defects Program; the Iowa Birth Defects Registry, the University of Iowa, and the Iowa Department of Public Health; and the Greenwood Genetic Center in South Carolina. Data also were analyzed from the Hawaii Birth Defects Monitoring Program, which includes data for some women who were not residents of the state. The systems differed in the size and racial/ethnic composition of the populations studied, the surveillance methods used, the completeness of ascertainment, and the availability and utilization of prenatal testing and pregnancy termination.

Results and Interpretation: Among all pregnancies ascertained in which the infant or fetus had anencephaly or spina bifida, the percentages that were electively terminated ranged from 9% in Arkansas to 42% in Atlanta and Hawaii, with a corresponding increase in the adjusted prevalence of these defects compared with the prevalence at birth. In each system, pregnancies associated with anencephaly were terminated more frequently than were those associated with spina bifida. These data indicate that the impact of prenatal diagnosis and subsequent pregnancy termination on the prevalence at birth of anencephaly and spina bifida differs among geographic areas and populations. Comprehensive surveillance for these defects requires inclusion of pregnancies that are prenatally diagnosed and then terminated.

Actions Taken: CDC will use these data to promote the inclusion of prenatally diagnosed and terminated pregnancies in estimates of the prevalence of anencephaly and spina bifida generated by birth defects surveillance programs in the United States. Including such pregnancies is crucial to the ability of these programs to monitor trends accurately and to establish the effectiveness of interventions, including the use of folic acid, for these defects.

INTRODUCTION

In the early 1970s, an association was documented between elevated alpha-fetoprotein levels in women during early pregnancy and the presence of anencephaly or open spina bifida, which are congenital neural tube defects (NTDs) of the brain and spinal cord, respectively (1,2). Since then, the ability to diagnose NTDs prenatally has progressed rapidly, with increased utilization of and improved techniques for both maternal serum alpha-fetoprotein (MSAFP) screening and high-resolution ultrasonography. Because many birth defects surveillance systems in the United States were established before these prenatal techniques were widely used, they ascertain defects primarily from hospital records among live-born infants only or among infants and fetuses beyond a certain gestational age (3). Pregnancies that are prenatally diagnosed with NTDs and subsequently terminated in an outpatient setting or before the specified gestational age often are not included in U.S. birth defects surveillance data.

The reported prevalence at birth of NTDs in the United States has steadily declined since the late 1960s (4), before the use of prenatal diagnostic testing became widespread. An undetermined proportion of this decline may reflect the fact that birth defects surveillance systems do not include NTD-affected pregnancies that are electively terminated after prenatal diagnosis. Reports from other countries (e.g., England, France, and Scotland) estimate that, in some areas in the mid-1980s, at least 80% of pregnancies affected by anencephaly and 40% of those affected by spina bifida were electively terminated (5). The only similar published estimate from the United States indicates that, in one area during 1990, the percentage of pregnancies affected by anencephaly that were electively terminated may have been even higher (6).

This report summarizes findings from birth defects surveillance systems in six states during the period 1985-1994 that were able to ascertain NTD-affected pregnancies which were prenatally diagnosed and then electively terminated. These findings estimate the reduction in the reported prevalence at birth of anencephaly and spina bifida in the United States resulting from prenatal diagnosis and subsequent pregnancy termination. The findings emphasize the importance of including prenatally diagnosed defects in NTD surveillance data.

METHODS

Population-based data about a) live-born and stillborn infants who had anencephaly and spina bifida * and b) pregnancies electively terminated after prenatal diagnosis of these defects were analyzed from five U.S. birth defects surveillance systems: the Arkansas Reproductive Health Monitoring System (ARHMS); the California Birth Defects Monitoring Program (CBDMP); CDC's Metropolitan Atlanta Congenital Defects Program (MACDP); the Iowa Birth Defects Registry, the University of Iowa, and the Iowa Department of Public Health; and the Greenwood Genetic Center (GGC) in South Carolina. Data were also analyzed from the Hawaii Birth Defects Monitoring Program (HBDMP), which includes data for some women who were not residents of the state. The years surveyed, the size of the populations studied, and the methods of ascertainment differed among the systems (Table_1). The case definitions of anencephaly and spina bifida also differed.

For the purpose of these analyses, all ascertained pregnancies in which the fetuses were prenatally diagnosed as having anencephaly or spina bifida and which were electively terminated were excluded from the calculations of prevalence at birth, regardless of the gestational age at termination. These estimates are based on the assumption that all NTD-affected pregnancies, had they not been terminated, would have been included in the prevalences of these defects at birth. The data were analyzed for each system by race/ethnicity because of previously reported race-specific differences in the prevalences at birth of these defects (7); race/ethnicity was either reported by the mother or obtained from patient records.

Arkansas: The ARHMS collected data from approximately two-thirds of the state's population born during the period 1985-1987 and from approximately half of the state's population born during the period 1988-1989. A case was defined as either a) anencephaly and/or spina bifida in a live-born or stillborn infant of greater than or equal to 22 weeks' gestation born from 1985 through 1989 or b) a pregnancy electively terminated during this same time period after prenatal diagnosis of these defects, regardless of the gestational age of the fetus. Cases were ascertained by review of medical records from hospitals, genetic service clinics, and specialty clinics, as well as through passive reporting by schools and community agencies. Race/ethnicity was categorized as either "white" or "black." ** Data from other racial and ethnic groups were not analyzed because of the limited number of cases among these groups. The population base from which defect prevalences were calculated consisted of 108,519 live-born and stillborn infants of greater than or equal to 20 weeks' gestation.

California: The CBDMP collected data from all counties in the state except Los Angeles, Ventura, and Riverside. A case was defined as either a) anencephaly and/or spina bifida in a live-born or stillborn infant of greater than or equal to 20 weeks' gestation born during the period June 1, 1989, through May 31, 1991, or b) a pregnancy electively terminated from February 1, 1989, through January 31, 1991, after prenatal diagnosis of these defects, regardless of the gestational age of the fetus. Cases were ascertained by review of medical and ultrasonography records at all hospitals and genetic clinics serving the population base. For this evaluation, race/ethnicity was categorized as either "white" or "other," with "other" including all racial and ethnic groups other than white. The population base from which defect prevalences were calculated consisted of 708,129 live-born and stillborn infants of greater than or equal to 20 weeks' gestation.

Atlanta, Georgia: The MACDP collected data from the five-county metropolitan Atlanta area. A case was defined as either a) anencephaly and/or spina bifida in a live-born or stillborn infant of greater than or equal to 20 weeks' gestation born during the period 1990-1991 or b) a pregnancy electively terminated after prenatal diagnosis of these defects, in which the fetus was of any gestational age but would have been at least 20 weeks' gestation during this same time period had the pregnancy not been terminated. Cases were ascertained by review of medical records from all hospitals, outpatient perinatal centers, and local genetic laboratories within the five-county metropolitan area, as well as from vital records. Race/ethnicity was categorized as either "white" or "black." ** Data from other racial and ethnic groups were not analyzed because of the limited number of cases among these groups. The population base from which defect prevalences were calculated consisted of 77,022 live-born infants.

Hawaii: The HBDMP collected data from the entire state. A case was defined as either a) anencephaly and/or spina bifida in a live-born or stillborn infant or fetus of any gestational age born in Hawaii during the period 1988-1994 or b) a pregnancy electively terminated in Hawaii during this same period after prenatal diagnosis of these defects, regardless of the gestational age of the fetus. Because cases were included regardless of whether the mother resided in Hawaii, the HBDMP data were not strictly population based. Cases were ascertained by review of medical records from all birth and tertiary hospitals, laboratories, and prenatal diagnostic centers in the state, as well as from vital records. Race/ethnicity was categorized as "white" or Asian. Data from other racial and ethnic groups, including Hispanic, were not analyzed because of the limited number of cases among these groups. The population base from which defect prevalences were calculated consisted of 148,092 live-born and stillborn infants and fetuses of any gestational age.

Iowa: Statewide data were collected from the Iowa Birth Defects Registry, the Maternal Serum Alpha-Fetoprotein Screening Program (directed by the Iowa Department of Public Health), and the Prenatal Diagnosis Clinic and Fetal Diagnosis and Treatment Unit of the University of Iowa Hospitals and Clinics. A case was defined as either a) anencephaly and/or spina bifida not associated with other major malformations or clinical syndromes in a live-born or stillborn infant of greater than or equal to 20 weeks' gestation born from 1985 through 1990 or b) a pregnancy electively terminated during this period after prenatal diagnosis of these defects, regardless of the gestational age of the fetus. The population base from which defect prevalences were calculated consisted of 234,113 live-born and stillborn infants of greater than or equal to 20 weeks' gestation, approximately 96% of whom were white. **

South Carolina: The GGC collected data from 14 counties that comprise approximately 30% of the state's population. A case was defined as either

  1. a pregnancy in which the mother had an estimated date of delivery during the period October 1, 1992, through September 30, 1993, that resulted in a live-born or stillborn infant of any gestational age with anencephaly and/or spina bifida or b) a pregnancy in which the mother had an estimated date of delivery during this same time period and which was electively terminated after prenatal diagnosis of these defects, regardless of the gestational age of the fetus. Cases were ascertained by continuous monitoring of MSAFP screening programs, obstetric offices, and fetal/neonatal autopsy programs serving the population base, as well as by periodic monitoring of hospital medical record departments and neonatal intensive-care units. Race/ethnicity was categorized as either "white" or "other." ** All but one of the NTD-affected infants and fetuses in the "other" category were black. ** The population base from which defect prevalences were calculated consisted of 16,641 live-born and stillborn infants who either were greater than or equal to 20 weeks' gestation or weighed greater than or equal to 350 grams at birth.

RESULTS

Among all pregnancies ascertained in which the infant or fetus had anencephaly or spina bifida, from 9% in Arkansas to 42% in Atlanta and Hawaii were electively terminated, with a corresponding increase in the adjusted prevalence of these defects compared with the prevalence at birth (Table_2). In each system, pregnancies associated with anencephaly were terminated more frequently (range: 20% in Arkansas to 69% in Hawaii) than were those associated with spina bifida (range: 3% in Arkansas to 29% in California). ***

The adjusted prevalences of anencephaly and spina bifida, both individually and combined, also differed among the systems. The prevalence in each category was highest in South Carolina and lowest in Hawaii. In every system, the adjusted prevalence of spina bifida was higher than that of anencephaly; however, the prevalence was only slightly higher in Atlanta.

Among all pregnancies ascertained in which the infant or fetus had anencephaly or spina bifida, the percentages that were electively terminated were available for each year of surveillance for Arkansas, Hawaii, and Iowa (Table_3). In Arkansas, this percentage more than tripled from 1985 (7%) to 1989 (23%); in Iowa, the percentage doubled from 1985 (13%) to 1990 (27%); in Hawaii, the percentage varied over the years without a discernible trend (range: 30% to 67%). **** However, in Hawaii, the adjusted prevalence of these defects almost doubled from the earlier years of surveillance (1988-1991, range: 0.28 to 0.57 per 1,000) to the later years (1992-1994, range: 0.97 to 1.11).

The effect of prenatal diagnosis and subsequent termination on the prevalence of anencephaly and spina bifida was compared among racial groups in Arkansas, Atlanta, and Hawaii (Table_4). The prevalences among racial groups in the other systems were not compared because of the limited number of cases among many of those groups. In both Arkansas and Atlanta, the prevalence at birth and adjusted prevalence of anencephaly and spina bifida were higher among white women than among black women. In Atlanta, a higher percentage of ascertained NTD-affected pregnancies was electively terminated among white women. In Arkansas, although a limited number of pregnancies among black women was ascertained, a higher percentage of those affected by anencephaly was electively terminated compared with those among white women.

In Hawaii, the adjusted prevalence of anencephaly and its prevalence at birth were similar among white women and Asian women; however, the prevalence at birth and adjusted prevalence of spina bifida were higher among white women. For both defects, the percentage of ascertained pregnancies that were subsequently terminated was higher among Asian women.

DISCUSSION

These data provide the first multistate, population-based estimate of the impact of prenatal diagnosis and subsequent pregnancy termination on the prevalence at birth of anencephaly and spina bifida in the United States. In some areas, the prevalence at birth of anencephaly was reduced by approximately 60%-70% and that of spina bifida by approximately 20%-30%.

Among the six systems, the percentage of NTD-affected pregnancies that were prenatally diagnosed and subsequently terminated varied widely. This variation may reflect differences in surveillance methods, completeness of ascertainment, availability and utilization of prenatal diagnostic testing, and acceptance of elective pregnancy termination. Comprehensive ascertainment of NTD-affected pregnancies that are subsequently terminated can be particularly difficult and variable among systems. In all six systems, some women who had NTD-affected pregnancies that were prenatally diagnosed and then terminated without being referred to a specialty center participating in the surveillance system might not have been included in the estimates of adjusted defect prevalence. As a result, both the number of prenatally diagnosed and terminated pregnancies and the estimated percentages of all NTD-affected pregnancies that were electively terminated reported by each system would have been decreased.

Effects of Different Methods for Ascertaining Cases

Statewide MSAFP screening programs, which can facilitate the prenatal diagnosis of fetuses with NTDs, are maintained in both California and Iowa. However, some MSAFP specimens might not have been submitted through these programs, thus lowering the number of prenatally diagnosed pregnancies ascertained by these systems. In addition, infants and fetuses with anencephaly and spina bifida associated with other major malformations were excluded from the case definition in Iowa. This exclusion might have lowered the ascertained prevalences of these defects at birth and the estimated percentages of all NTD-affected pregnancies that were electively terminated in Iowa compared with other systems.

Because MSAFP screening was not widely available in local health departments in Arkansas until the late 1980s, the estimated percentage of all NTD-affected pregnancies that were electively terminated reported by Arkansas was low. The availability of screening may partially account for the increase in this percentage during 1988 and 1989. Decreased funding for the surveillance program may also have affected case-finding in Arkansas during 1988 and 1989. In Atlanta, an MSAFP screening program has not been established; therefore, prenatally diagnosed pregnancies were ascertained primarily through review of ultrasonography records and amniotic fluid alpha-fetoprotein results.

Similarly, in Hawaii, cases were ascertained primarily through record review at prenatal diagnostic centers and birth hospitals. Because these records did not always indicate the final outcome of the pregnancy, it is unknown whether four of the NTD-affected pregnancies in Hawaii (two with anencephaly and two with spina bifida) were electively terminated. If all four of these pregnancies were terminated after prenatal diagnosis, the estimated percentage of NTD-affected pregnancies that were terminated in Hawaii would have been higher (Table_2, Table_3). In addition, ascertainment of prenatally diagnosed pregnancies that were electively terminated was begun for all years of the surveillance in 1994 on a retrospective basis. The comprehensiveness of case ascertainment among these pregnancies might therefore be lower than that among live-born and stillborn infants and fetuses.

In contrast, the South Carolina system was based on direct contact with both local MSAFP programs and individual obstetricians and pathologists. This method might have provided more comprehensive ascertainment of prenatally diagnosed pregnancies in South Carolina compared with the other systems and might have contributed to the increased prevalences of these defects reported by South Carolina. However, the methods used to identify live-born and stillborn infants with anencephaly and spina bifida from hospital records in South Carolina may have resulted in less complete ascertainment of these cases than in other systems, resulting in a lowering of the estimated prevalence at birth in that state.

This analysis could not determine whether the decreased prevalences reported from Hawaii and the increased prevalences reported from South Carolina were true or whether they resulted from the differences in surveillance methods among the systems. In addition, the increased prevalences reported from South Carolina may also have resulted from the limited total number of NTD-affected pregnancies ascertained by that system.

Factors Affecting Calculations of NTD Prevalence at Birth

With regard to the data for each year of surveillance, the increased percentage of all ascertained NTD-affected pregnancies that were electively terminated in the later years in the Arkansas and Iowa systems may reflect an increase in the availability and utilization of prenatal diagnostic procedures, an increased ability of physicians to diagnose NTDs prenatally, an increase in the referral of pregnancies suspected to be affected with NTDs to subspecialists, and improved case ascertainment. The lack of a similar trend in these percentages over time in the Hawaii system may reflect the relatively later years of surveillance reported by that system and a more uniform pattern of prenatal care practices compared with the other systems. The reason for the increase in prevalence at birth and adjusted prevalence in Hawaii for 1992-1994 compared with 1988-1991 is unclear. Neither surveillance techniques nor case ascertainment methods changed during those years. Continued surveillance should clarify whether this increase in prevalence represents a persistent trend.

The comparison of data among racial groups from Arkansas, Atlanta, and Hawaii suggests an increased adjusted prevalence of anencephaly and spina bifida among white women compared with black women and an increased adjusted prevalence of spina bifida among white women compared with Asian women. These race-specific differences in the percentage of pregnancies terminated may have resulted from a) differences in availability and utilization of prenatal procedures, including elective termination, or b) the limited number of NTD-affected pregnancies among some racial groups ascertained by these systems.

In the six surveillance systems included in this report, all NTD-affected pregnancies that were subsequently terminated were excluded from the calculations of prevalence at birth of anencephaly and spina bifida. However, in some U.S. birth defects surveillance systems, only NTD-affected pregnancies that were electively terminated beyond a specific gestational age are included in the calculations of prevalence at birth. In addition, some surveillance systems may include infants with encephalocele and other NTDs in their case ascertainment. As a consequence, the reduction in the estimates of prevalence at birth resulting from prenatal diagnosis and subsequent termination calculated from some surveillance data may be smaller than reflected in this report. For example, if the MACDP data had included only NTD-affected pregnancies that were electively terminated at greater than or equal to 20 weeks and if infants with encephalocele had been included in the MACDP case definition, the reduction in the prevalences at birth of NTDs attributable to prenatal diagnosis and elective termination would have been approximately 30% (8), not the 42% cited in this report.

CONCLUSIONS

The findings in this report indicate that the impact of prenatal diagnosis and subsequent pregnancy termination on surveillance for anencephaly and spina bifida can differ considerably among geographic areas, among populations, and over time. This variation underscores the necessity of monitoring this impact for each population -- or subgroup of a population -- studied. The findings also demonstrate the considerable magnitude of the reduction in prevalence at birth of these defects resulting from the widespread use of prenatal diagnostic techniques. Comprehensive surveillance for NTDs can no longer be conducted without ascertaining pregnancies that are prenatally diagnosed and then electively terminated.

Such comprehensive surveillance can play a key role in evaluating the effectiveness of preventive measures for NTDs. Improving the dietary level of folic acid (a B vitamin) has been demonstrated to prevent the occurrence of many NTDs (9,10). This finding represents a historic opportunity for the prevention of birth defects. In 1991 and 1992, CDC published recommendations for the use of folic acid to prevent NTDs (11,12). As these recommendations are implemented and the use of folic acid becomes more widespread, its effect on the prevalence of NTD-affected pregnancies must be closely and accurately monitored. If surveillance is to be used to monitor the effectiveness of this prevention and any resultant decline in the prevalence of NTDs attributable to folic acid use, pregnancies that are electively terminated after prenatal diagnosis of an NTD must be included in NTD surveillance. Otherwise, evaluation of a reduction in the prevalence of NTDs attributable to folic acid cannot be distinguished from the decrease resulting from prenatal diagnosis and elective termination.

References

  1. Brock DJH, Sutcliffe RG. Alpha-fetoprotein in the antenatal diagnosis of anencephaly and spina bifida. Lancet 1972;2:197-9.

  2. Wald NJ, Brock DJH, Bonnar J. Prenatal diagnosis of spina bifida and anencephaly by maternal serum-alpha-fetoprotein measurement: a controlled study. Lancet 1974;1:765-7.

  3. Edmonds LD, Layde PM, James LM, et al. Congenital malformations surveillance: two American systems. Int J Epidemiol 1981;10:247-52.

  4. Yen IH, Khoury MJ, Erickson JD, et al. The changing epidemiology of neural tube defects: United States, 1968-1989. Am J Dis Child 1992;146: 857-61.

  5. EUROCAT Working Group. Prevalence of neural tube defects in 20 regions of Europe and the impact of prenatal diagnosis, 1980-1986. J Epidemiol Community Health 1991;45:52-8.

  6. Limb CJ, Holmes LB. Anencephaly: changes in prenatal detection and birth status, 1972 through 1990. Am J Obstet Gynecol 1994;170:1333-8.

  7. CDC. Spina bifida incidence at birth -- United States, 1983-1990. MMWR 1992;41:497-500.

  8. Roberts HE, Moore CA, Fernhoff PM, Cragan JD, Khoury MJ. The impact of prenatal diagnosis on the birth prevalence of neural tube defects, metropolitan Atlanta, 1990-1991 {abstract}. Teratology 1994;49:386.

  9. MRC Vitamin Study Research Group. Prevention of neural tube defects: results of the Medical Research Council Vitamin Study. Lancet 1991;338: 131-7.

  10. Czeizel AE, Dudas I. Prevention of the first occurrence of neural-tube defects by periconceptional vitamin supplementation. N Engl J Med 1992;327:1832-5.

  11. CDC. Use of folic acid for prevention of spina bifida and other neural tube defects -- 1983-1991. MMWR 1991;40:513-6.

  12. CDC. Recommendations for the use of folic acid to reduce the number of cases of spina bifida and other neural tube defects. MMWR 1992;41(No. RR-14):1-7.

The data do not distinguish between open and closed spina bifida.

** Whether Hispanic infants were included in this category is unknown.

*** It is unknown whether four of the NTD-affected pregnancies in Hawaii (two with anencephaly, two with spina bifida) were electively terminated. If all four pregnancies were prenatally diagnosed and subsequently terminated, 73% of the pregnancies with anencephaly, 26% of those with spina bifida, and 46% of the total NTD-affected pregnancies from Hawaii would have been electively terminated.

**** It is unknown whether four of the NTD-affected pregnancies in Hawaii (two with anencephaly, two with spina bifida) were electively terminated. If all four of these pregnancies were prenatally diagnosed and subsequently terminated, the range of NTD-affected pregnancies that were electively terminated in Hawaii would have been 33% to 67%.




Table_1
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TABLE 1. Comparison of selected birth defects surveillance systems -- United States
====================================================================================================================================================================
System                            Years surveyed    Reporting area            Total no. of births *   Methods of ascertainment
----------------------------------------------------------------------------------------------------------------------------------------------
Arkansas Reproductive             1985-1989         1985-1987: 67% of the            108,519          Record review: hospitals, genetic and
  Monitoring System                                   state population;                                 specialty health clinics;
                                                    1988-1989: 50% of the                             Passive reporting: schools, community
                                                      state population                                  agencies

California Birth Defects          1989-1991 +       All counties except Los          708,129          Record review: hospitals, genetic
  Monitoring Program                                  Angeles, Ventura, and                             clinics, and ultrasonography records
                                                      Riverside

Metropolitan Atlanta              1990-1991         Five-county                      77,022           Record review: hospitals, genetic
  Congenital Defects Program                          metropolitan Atlanta                              laboratories, perinatal offices, and
                                                      area                                              vital records

Hawaii Birth Defects              1988-1994         Statewide                        148,092          Record review: hospitals, laboratories,
  Monitoring Program                                                                                    prenatal diagnostic centers, and vital
                                                                                                        records

Iowa Birth Defects Registry, the  1985-1990         Statewide                        234,113          Data linkage: Birth Defects Registry,
  University of Iowa, and the                                                                           Prenatal Diagnosis Clinic, Fetal
  Iowa Department of                                                                                    Diagnosis and Treatment Unit, and the
  Public Health                                                                                         MSAFP Screening Program

Greenwood Genetic Center          1992-1993 &       14 upstate counties              16,641           Record review: MSAFP and autopsy
  (South Carolina)                                                                                      programs, obstetric offices
                                                                                                      Periodic hospital reports
----------------------------------------------------------------------------------------------------------------------------------------------
* Includes live-born and stillborn infants >=20 weeks' gestation in the California, Iowa, and Arkansas systems; live-born infants in the Atlanta system; live-born
  and stillborn infants who either were >20 weeks' gestation or weighed >=350 grams at birth in the South Carolina system; and live-born and stillborn infants
  or fetuses of any gestational age in the Hawaii system.
+ Data were collected for live-born and stillborn infants who were born from June 1, 1989, through May 31, 1991. Data were collected for pregnancies that
  were terminated from February 1, 1989, through January 31, 1991.
& Data were collected for pregnancies with an estimated date of delivery from October 1, 1992, through September 30, 1993.
MSAFP = Maternal serum alpha-fetoprotein
====================================================================================================================================================================

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Table_2
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TABLE 2. Prevalence at birth of anencephaly and spina bifida and adjusted prevalence after prenatal diagnosis and elective
termination, * by birth defect and system -- United States
=================================================================================================================================================================
                         Prevalence at birth +          No. of           Adjusted prevalence &        Percentage of
Birth defect/          --------------------------     terminated      ---------------------------      pregnancies
  System               No.    Rate     (95% CI)       pregnancies     No.     Rate     (95% CI)       terminated @
-------------------------------------------------------------------------------------------------------------------
Anencephaly
ARHMS                   32    0.29    (0.20-0.42)           8          40     0.37    (0.26-0.55)          20
CBDMP                  143    0.20    (0.17-0.24)         142         285     0.40    (0.36-0.45)          50
MACDP                   15    0.19    (0.11-0.32)          22          37     0.48    (0.34-0.66)          59
HBDMP                   12    0.08    (0.04-0.14)          31          45 **  0.30    (0.22-0.41)          69
Iowa Birth Defects
  Registry ++           62    0.27    (0.20-0.34)          20          82     0.35    (0.28-0.43)          24
GGC                      4    0.24    (0.06-0.62)           6          10     0.60    (0.29-1.11)          60

Spina bifida
ARHMS                   70    0.65    (0.50-0.82)           2          72     0.66    (0.52-0.84)           3
CBDMP                  250    0.35    (0.31-0.40)         103         353     0.50    (0.45-0.55)          29
MACDP                   29    0.38    (0.25-0.54)          10          39     0.51    (0.36-0.69)          26
HBDMP                   45    0.30    (0.22-0.41)          14          61 **  0.41    (0.32-0.53)          23
Iowa Birth Defects
  Registry             104    0.44    (0.36-0.54)          25         129     0.55    (0.46-0.65)          19
GGC                     12    0.72    (0.37-1.26)           4          16     0.96    (0.55-1.56)          25

Total
ARHMS                  102    0.94    (0.76-1.14)          10         112     1.03    (0.85-1.24)           9
CBDMP                  393    0.55    (0.50-0.61)         245         638     0.90    (0.83-0.97)          38
MACDP                   44    0.57    (0.42-0.77)          32          76     0.99    (0.78-1.23)          42
HBDMP                   57    0.38    (0.29-0.50)          45         106 **  0.72    (0.59-0.87)          42
Iowa Birth Defects
  Registry             166    0.71    (0.61-0.83)          45         211     0.90    (0.78-1.07)          21
GGC                     16    0.96    (0.55-1.56)          10          26     1.56    (1.02-2.29)          38
-------------------------------------------------------------------------------------------------------------------
 * Both prevalences are per 1,000 live-born and stillborn infants >=20 weeks' gestation in the California, Iowa, and Arkansas systems; per 1,000 live-born
   infants in the Atlanta system; per 1,000 live-born and stillborn infants who were >20 weeks' gestation or had a birth weight of >=350 grams in the South
   Carolina system; and per 1,000 live-born and stillborn infants or fetuses of any gestational age in the Hawaii system.
 + Includes live-born and stillborn infants >=20 weeks' gestation in the California, Iowa, South Carolina, and Atlanta systems; live-born and stillborn infants
   >=22 weeks' gestation in the Arkansas system; and live-born and stillborn infants and fetuses of any gestational age in the Hawaii system.
 & Includes a) pregnancies that were electively terminated and b) infants who were included in the calculations for birth prevalence.
 @ Percentage of pregnancies included in the calculations for adjusted prevalence that were electively terminated.
** It is unknown whether four of the prenatally diagnosed pregnancies in Hawaii (two with anencephaly, two with spina bifida) were electively terminated.
   If all four pregnancies had been prenatally diagnosed and subsequently terminated, 73% of the pregnancies with anencephaly, 26% of those with spina
   bifida, and 46% of the total NTD-affected pregnancies from Hawaii would have been electively terminated.
++ The Iowa Birth Defects Registry includes data from the University of Iowa and the Iowa Department of Public Health.

ARHMS = Arkansas Reproductive Health Monitoring System
CBDMP = California Birth Defects Monitoring Program
MACDP = Metropolitan Atlanta Congenital Defects Program
HBDMP = Hawaii Birth Defects Monitoring Program
GGC = Greenwood Genetic Center (South Carolina)

95% CI = 95% confidence intervals
=================================================================================================================================================================

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Table_3
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TABLE 3. Prevalence at birth of anencephaly and spina bifida and adjusted prevalence after prenatal diagnosis and elective
termination, * by year, selected birth defects surveillance systems -- United States
=============================================================================================================================================================
                  Prevalence at birth +          No. of          Adjusted prevalence &        Percentage of
                --------------------------     terminated      --------------------------      pregnancies
System/Year     No.    Rate     (95% CI)       pregnancies     No.    Rate     (95% CI)       terminated @
-----------------------------------------------------------------------------------------------------------
ARHMS
 1985            28    1.14    (0.76-1.65)          2           30    1.23    (0.83-1.75)           7
 1986            26    1.08    (0.71-1.59)          0           26    1.08    (0.71-1.59)          --
 1987            19    0.91    (0.55-1.43)          1           20    0.96    (0.59-1.48)           5
 1988            12    0.62    (0.32-1.08)          2           14    0.72    (0.39-1.21)          14
 1989            17    0.86    (0.50-1.37)          5           22    1.11    (0.70-1.68)          23

HBDMP
 1988             7    0.34    (0.14-0.71)          4           11    0.54    (0.27-1.00)          36
 1989             8    0.38    (0.12-0.89)          4           12    0.57    (0.30-1.00)          33
 1990             5    0.22    (0.07-0.52)          6           12 ** 0.54    (0.28-0.94)          50
 1991             2    0.09    (0.01-0.34)          4            6    0.28    (0.10-0.61)          67
 1992            12    0.56    (0.29-0.98)         10           22    1.00    (0.65-1.56)          45
 1993            13    0.62    (0.33-1.06)          6           20 ** 0.97    (0.59-1.50)          30
 1994            10    0.49    (0.23-0.89)         11           23 ** 1.11    (0.61-1.87)          48

Iowa ++
 1985            34    0.83    (0.57-1.15)          5           39    0.95    (0.67-1.29)          13
 1986            29    0.75    (0.50-1.07)          4           33    0.85    (0.59-1.20)          12
 1987            29    0.77    (0.51-1.10)          6           35    0.92    (0.64-1.29)          17
 1988            21    0.55    (0.34-0.84)          7           28    0.74    (0.49-1.06)          25
-----------------------------------------------------------------------------------------------------------
 * Both prevalences are per 1,000 live-born and stillborn infants >=20 weeks' gestation in the Arkansas and Iowa systems, and per 1,000 live-born and
   stillborn infants or fetuses of any gestational age in the Hawaii system.
 + Includes live-born and stillborn infants >=20 weeks' gestation in the Iowa system, live-born and stillborn infants >=22 weeks' gestation in the Arkansas
   system, and live-born and stillborn infants and fetuses of any gestational age in the Hawaii system.
 & Includes a) pregnancies that were electively terminated and b) infants who were included in the calculations for prevalence at birth.
 @ Percentage of pregnancies included in the calculations for adjusted prevalence that were electively terminated.
** It is unknown whether four of the prenatally diagnosed pregnancies in Hawaii (two with anencephaly, two with spina bifida) were electively terminated.
   If all four pregnancies had been prenatally diagnosed and sibsequently terminated, 58% of the NTD-affected pregnancies from 1990, 35% of those from
   1993, and 57% of those from 1994 in Hawaii would have been electively terminated.
++ The Iowa Birth Defects Registry includes data from the University of Iowa and the Iowa Department of Public Health.

ARHMS = Arkansas Reproductive Health Monitoring System
HBDMP = Hawaii Birth Defects Monitoring Program

95% CI = 95% confidence intervals
=============================================================================================================================================================

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Table_4
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TABLE 4. Prevalence at birth of anencephaly and spina bifida and adjusted prevalence after prenatal diagnosis and elective
termination, * by race-selected birth defects surveillance systems -- United States
===================================================================================================================================================================
                 Prevalence at birth +         No. of         Adjusted prevalence &       Percentage of
                ------------------------     terminated      ------------------------      pregnancies
System/Race     No.   Rate    (95% CI)       pregnancies     No.   Rate    (95% CI)       terminated @
-------------------------------------------------------------------------------------------------------
Anencephaly

 ARHMS
  White          27   0.32   (0.21-0.47)          6           33   0.39   (0.27-0.55)          18
  Black           3   0.13   (0.03-0.39)          2            5   0.22   (0.07-0.51)          40
 MACDP
  White           9   0.21   (0.10-0.40)         16           25   0.58   (0.37-0.86)          64
  Black           5   0.16   (0.05-0.37)          3            8   0.25   (0.11-0.50)          38
 HBDMP
  White           3   0.08   (0.02-0.24)          6            9   0.24   (0.11-0.46)          67
  Asian           6   0.07   (0.02-1.46)         17           23   0.27   (0.16-0.38)          74

Spina bifida

 ARHMS
  White          57   0.68   (0.51-0.88)          2           59   0.70   (0.53-0.97)           3
  Black          12   0.53   (0.27-0.92)          0           12   0.53   (0.27-0.92)          --
 MACDP
  White          18   0.42   (0.25-0.66)          8           26   0.60   (0.39-0.88)          31
  Black          11   0.35   (0.17-0.62)          2           13   0.41   (0.22-0.70)          15
 HBDMP
  White          16   0.43   (0.25-0.70)          2           18   0.48   (0.29-0.76)          11
  Asian          27   0.30   (0.20-0.44)          7           34   0.39   (0.26-0.53)          21

Total

 ARHMS
  White          84   1.00   (0.79-1.23)          8           92   1.09   (0.88-1.34)           9
  Black          15   0.66   (0.34-1.09)          2           17   0.75   (0.44-1.20)          12
 MACDP
  White          27   0.63   (0.41-0.91)         24           51   1.18   (0.88-1.55)          47
  Black          16   0.51   (0.29-0.82)          5           21   0.66   (0.41-1.01)          24
 HBDMP
  White          19   0.51   (0.31-0.80)          8           27   0.72   (0.48-1.10)          30
  Asian          33   0.37   (0.25-0.52)         24           57   0.63   (0.48-0.82)          42
-------------------------------------------------------------------------------------------------------
* Both prevalences are per 1,000 live-born and stillborn infants >=20 weeks' gestation in the Arkansas system; per 1,000 live-born infants in the Atlanta system;
  and per 1,000 live-born and stillborn infants or fetuses of any gestational age in the Hawaii system.
+ Includes live-born and stillborn infants >=22 weeks' gestation in the Arkansas system; live-born and stillborn infants >=20 weeks' gestation in the Atlanta
  system; and live-born and stillborn infants and fetuses of any gestational age in the Hawaii system.
& Includes a) pregnancies that were electively terminated and b) infants who were included in the calculations for prevalence at birth.
@ Percentage of pregnancies included in the calculations for adjusted prevalence that were electively terminated.

ARHMS = Arkansas Reproductive Health Monitoring System
MACDP = Metropolitan Atlanta Congenital Defects Program
HBDMP = Hawaii Birth Defects Monitoring Program

95% CI = 95% confidence intervals
===================================================================================================================================================================

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