CLASSIFICATION OF DATA One of the principal values of vital statistics data is realized through the presentation of rates computed by relating the vital events of a class to the population of a similarly defined class. Vital statistics and population statistics, therefore, must by classified according to similarly defined systems and tabulated in comparable groups. Even the variables common to both, such as geographic area, age, race, and sex, have been similarly classified and tabulated, differences between the enumeration method of obtaining population data and the registration method of obtaining vital statistics data may result in significant discrepancies. The general rules used to classify geographic and personal items for live births are set forth in "Vital Statistics Classification and Coding Instructions for Live Birth Records, 1985", NCHS Instruction Manual, Part 3a. The classification of certain important items is discussed in the following pages. Classification by occurrence and residence All but three tabulations for States and other areas within the United States are by place of mother's residence. These three tabulations (1-49, 1-50, and 2-1) show births by place of occurrence. Births to U.S. residents occurring outside this country are not reallocated to the United States. In tabulations by place of residence, births occurring to U.S. citizens and to resident aliens are allocated to the usual place of residence of the mother in the United States as reported on the birth certificate. Beginning in 1970, births to nonresidents of the United States occurring in the United States are excluded from these tabulations. From 1966 to 1969, births occurring in the United States to mothers who were nonresidents of the United States were considered as births to residents of the exact place of occurrence; in 1964 and 1965 all such births were allocated to "balance of county" of occurrence even if the birth had occurred in a city. The change in coding beginning in 1970 to exclude births to nonresidents of the United States from residence data significantly affects the comparability of data with years before 1970 only for Texas. In 1985 births to residents of Mexico constituted 84.4 percent of the 4,503 nonresident births in the United States. No evaluation of the effect of the change in procedure between 1965 and 1966 has been made. For the total United States the tabulations by place of residence and by place of occurrence are not identical. Births to nonresidents of the United States are included in data by place of occurrence but excluded from data by place of residence, as previously indicated. Residence error-A nationwide test of birth-registration completeness in 1950 provided measures of residence error for natality statistics. According to this test, errors in residence reporting for the country as a whole tend to overstate the number of births to residents of urban areas and understate the number of births to residents of other areas. This tendency has assumed special importance because of a concomitant development-the increased utilization of hospitals in cities by residents of nearby places-with the result that a number of births are erroneously reported as having occurred to residents of urban areas. Another factor that contributes to this overstatement of urban births is the customary procedure of using "city" addresses for persons living outside city limits. clsnat85.doc - Page 1 Incomplete residence-Beginning in 1963, when only the State of residence is reported with no city or county specified, and the State named is different from the State of occurrence, the birth is allocated to the largest city of the State of residence. Before 1973 such births were allocated to the exact place of occurrence. Geographic classification The rules followed in the classification of geographic areas for live births are contained in the instruction manual mentioned previously. The geographic code structure for 1985 is given in another manual, "Vital Records Geographic Classification, 1982." United States-In the statistical tabulations, "United States" refers only to the aggregate of the 50 States and the District of Columbia. Alaska has been included in the U.S. tabulations since 1959 and Hawaii since 1960. Standard metropolitan statistical areas-The standard metropolitan statistical areas (SMSA's) used in this report are those established by the U.S. Office of Management and Budget (1981a, pp. 1-20.) from final 1980 census population counts and used by the U.S. Bureau of the Census except in the New England States. Except in the New England States, an SMSA is a county or group of contiguous counties containing either a city of 50,000 inhabitants or more or an urbanized area of 50,000 with a total metropolitan population of at least 100,000. In addition to the county or counties containing such a city or urbanized areas, contiguous counties are included in an SMSA if, according to a specified criteria, they are essentially metropolitan in character and are socially and economically integrated with the central city or urbanized area (U.S. Office of Management and Budget, 1981b, p. 420). In the New England States the U.S. Office of Management and Budget used towns and cities rather than counties as geographic components of SMSA's. The National Center for Health Statistics cannot, however, use the SMSA classification for these States because its data are not coded to identify all towns. Instead, the New England County Metropolitan Areas (NECMA's) are used. These areas are established by the U.S. Office of Management and Budget (1975, pp. 89-90; 1981b, p. 420) and are made up of county units. Metropolitan and nonmetropolitan counties-Independent cities and counties included in SMSA's or NECMA's are included in data for metropolitan counties; all other counties are classified as nonmetropolitan. Population-size groups-Beginning in 1982 vital statistics data for cities and certain other urban places have been classified according to the population enumerated in the 1980 Census of Population. Data are available for individual cities and other urban places of 10,000 or more population. Data for the remaining areas not separately identified are shown in the tables under the heading "Balance of area" or "Balance of county". Classification of areas for the years 1970-81 was determined by the population enumerated in the 1970 Census of Population. As a result of changes in the enumerated population between 1970 and 1980, some urban places identified in previous reports are no longer included, and a number of other urban places have been added. Urban places other than incorporated cities for which vital statistics are shown in this report include the following: clsnat85.doc - Page 2 Each town in New England, New York, and Wisconsin and each township in Michigan, New Jersey, and Pennsylvania that had no incorporated municipality as a subdivision and had either 25,000 inhabitants more or a population of 10,000 to 25,000 and a density of 1,000 persons or more per square mile. Each county in States other than those indicated above that had no incorporated municipality within its boundary and had a density of 1,000 persons or more per square mile. (Arlington County, Virginia, is the only county classified as urban under this rule.) Each place in Hawaii with 10,000 or more population. (There are no incorporated cities in Hawaii.) Race or national origin The race or national origin shown in a tabulation is that of the newborn child. Classification of the child's race or national origin for statistical purposes is based on the race or national origin of the parents. The categories are "White," "Black," "American Indian," "Chinese," "Japanese," "Hawaiian," "Filipino," "Other Asian or Pacific Islander," and "Other" races. Before 1978 the category "Other Asian or Pacific Islander" was not identified separately but included with "Other" races. The separation of this category allows identification of the category "Asian or Pacific Islander" by combining the new category "Other Asian or Pacific Islander" with Chinese, Japanese, Hawaiian, and Filipino. If the parents are of different races or national origins, the following rules are used to assign race or national origin to the newborn child. When only one parent is white, the child is assigned the other parent's race or national origin. When neither parent is white, the child is assigned the father's race or national origin with one exception; if either parent is Hawaiian or part-Hawaiian, the child is assigned to Hawaiian. If race is missing for one parent, the child is assigned the race of the parent for whom race is given. When information on race is missing for both parents, the race of the child is considered not stated and the birth is allocated according to rules discussed in the section "Race or national origin not stated." White-The category "White" comprises births reported as white and births where race is reported as Hispanic. Before 1964, all births for which race or national origin was not stated were classified as white. Beginning in 1964 changes in the procedures for allocating race when race or national origin is not stated have changed the composition of this category. (See discussion on "Race or national origin not stated.") All other-The category "All other" comprises black, American Indian, Chinese, Japanese, Hawaiian and part-Hawaiian, Filipino, other Asian or Pacific Islander including Asian Indian, and "Other." Aleuts and Eskimos are included in "American Indian." If the race or national origin of an Asian parent is ill-defined or not clearly identifiable with one of the categories used in the classification (for example, if "Oriental" is entered), an attempt is made to determine the specific race or national origin from the entry place of birth. If the birthplace is China, Japan, or the Philippines, the parents's race is assigned to that category. When race cannot be determined from birthplace, it is assigned to the category "Other Asian or Pacific Islander." clsnat85.doc - Page 3 Race or national origin not stated-The race of a child is considered not stated in those cases in which information for both parents is missing. Before 1964 all such cases were tabulated as white. From 1964 through 1968 the race of the child was allocated by the computer as follows: If the race of the preceding record was white, the assignment was to white; otherwise the assignment was to black. Beginning in 1969 the race of the child has been allocated electronically according to the specific race of the child on the preceding record. Consequently, some of the not-stated frequencies that had been previously assigned to the black category may now be assigned to one of the other race or national origin categories. Nearly all statistics by race or national origin for the United States as a whole in 1962 and 1963 are affected by a lack of information for New Jersey, which did not report parents' race in those years. Birth rates by race for those years are computed on a population base that excludes New Jersey. (For the method of estimating the U.S. population by age, sex, and race excluding New Jersey in 1962 and 1963, see Vital statistics of the Unites States, 1963, volume I, page 4-8.) Estimates of births to unmarried mothers by race for the United States, which include special estimates for New Jersey for 1962 and 1963, have been prepared and are shown in table 1-31. Interracial parentage-Because of interracial parentage, the number of births for each racial or national origin group classified according to the child's race by the preceding rules differs from the number of births classified according to the mother's race. For white and black births, the differences are relatively small. In 1985 there were 1.6 percent more white mothers than were births classified as white and 4.3 percent fewer black mothers than births classified as black. The number of mothers of other racial or national origin groups was considerably lower than then the number of births classified according to the child's race: American Indian, 20.2 percent; Chinese, 7.9 percent; Japanese, 17.9 percent; Hawaiian, 31.3 percent; Filipino, 6.6 percent: Other Asian and Pacific Islander, 7.0 percent; and "Other," 19.8 percent. Age of mother The birth certificate asks for "Age (at time of this birth)." The age of the mother is edited for upper and lower limits. When mothers are reported to be under 10 years of age or 50 years and over, the age of the mother is considered not stated and is assigned as described below. Age-specific birth rates shown in this report are based on populations of women by age, which are prepared by the U.S. Bureau of the Census. In census years the decennial census counts are used. In intercensal years, estimates of the population of women by age are published by the U.S. Bureau of the Census in Current population reports. The 1980 Census of Population derived age in completed years as of April 1, 1980, from the responses to questions on age at last birthday and month and year of birth, with the latter given preference. In the 1960 and 1970 censuses, age was also derived from month and year of birth. "Age in completed years" was asked in censuses before 1960. This was nearly the equivalent of the birth certificate question, which the 1950 test of matched birth and census records confirms by showing a high degree of consistency in the reporting of age in these two sources (National Vital Statistics Division, 1962). Median age of mother-Median age is the value that divides an age clsnat85.doc - Page 4 distribution into two equal parts, one-half of the value being less and one-half being greater. Median ages of mothers for 1960 to the present have been computed from birth rates for 5-year age groups rather than from birth frequencies. This eliminates the effects of changes in the age composition of the childbearing population over time. Changes in the median ages from year to year thus can be attributed solely to changes in the age-specific birth rates. Not stated age of mother-Beginning in 1964 birth records with age of mother not stated have been allocated according to the age appearing on the record previously processed for a mother of identical race and having the same total birth order (total of fetal deaths and live births). In 1963 birth records with age not stated were allocated according to the age appearing on the record previously processed for a mother of identical race and parity (number of live births). For 1960-62, ages not stated were distributed in proportion to the known ages for each racial group. Before 1960 this was done for age-specific birth rates but not for the birth frequency tables, which showed a separate category for age not stated. Age of father Age of father is coded as stated on the birth certificate. If the age is under 10 years, it is considered not stated and grouped with those cases for which age is not stated on the certificate. Information on father's age is often missing on birth certificates of children born to unwed mothers, greatly inflating the number of "not stated" in all tabulations by age of father. In computing birth rates by age of father, births tabulated as age of father not stated are distributed in the same proportions as births with known age within each 5-year age classification of the mother. This procedure is done separately by race. The resulting distributions are summed to form a composite frequency distribution which is the basis for computing birth rates by age of father. This procedure avoids the distortion in rates that would result if the relationship between age of mother and age of father were disregarded. Live-birth order and parity Birth order and parity classifications shown in this volume refer to the total number of live births the mother has had including the 1985 birth. Fetal deaths are excluded. Birth order indicates what number the present birth represents; for example, a baby born to a mother who has had two previous live births (even if one or both are not now living) has a birth order of three. Parity indicates how many live births a mother has had. Before delivery, a mother having her first baby has a parity of zero and a mother having her third baby has a parity of two. After delivery the mother of a baby who is a first live birth has a parity of one and the mother of a baby who is a third live birth has a parity of three. Birth order and parity are determined from two items on the birth certificate, "Live births-now living" and "Live births-now dead." Not stated birth order-Before 1969 if both of these items were blank, the birth was considered a first birth. Beginning in 1969, births for which the pregnancy history item were not completed have been tabulated as birth order not stated. As a result of this revised procedure, 22,686 births in 1969 that clsnat85.doc - Page 5 would have been assigned to the "First birth order" category under the old rules were assigned to the "Not stated" category. All births tabulated in the "Not stated birth order" category are excluded from the computation of percents. In computing birth rates by live-birth order, births tabulated as birth order not stated are distributed in the same proportion as birth of known live-birth order. Dates of last live birth and last fetal death Date of last live birth and date of last fetal death were added to the U.S. Standard Certificate of Live Birth in 1968 for the purpose of providing information on child spacing and pregnancy intervals. Tabulations of these items were presented for the first time in 1969. In 1978 the item "Date of last fetal death" was reworded to "Date of last other termination" to insure inclusion of both spontaneous fetal deaths and induced terminations of pregnancy. In 1985 this information was obtained from all States except Texas. Intervals since last live birth and last other termination-These data are computed from the date of birth, date of last live birth, and date of last other termination. The interval since last live birth is the difference between the date of last live birth and the date of present birth; the interval since last other termination is the difference between the date of last other termination and the date of present birth. For an interval to be computed, both the month and year of the last live birth or the last other termination must be valid. These intervals are computed only for events to mothers who have had at least one previous delivery. Births for which the interval since last live birth or last other termination is not stated are excluded from the computation of percents and means. Interval since last pregnancy and outcome of last pregnancy-These data are derived from the computed intervals since the last live birth and the last other termination. Before 1982, the outcome of the last pregnancy was considered to be not stated if the interval since either the last live birth or the last fetal death was not computed because only the year of the event was recorded. Beginning in 1982, the outcome of the last pregnancy was derived from such records if the year of the last live birth and the year of the last fetal death were not the same. The effect of this revised procedure is to reduce substantially the number of records with outcome of last pregnancy not stated. In addition, for such records, the interval since the termination of the last pregnancy was determined if both the month and year were reported for the event immediately preceding the current live birth. Before 1982, the interval since the termination of the last pregnancy was considered not stated for such births. Births for which the interval since last pregnancy is not stated are excluded from the computation of percents and means. Zero interval-An interval of zero months since the last live birth or fetal death indicates the secondborn of a set of twins, the second or third born of a set of triplets, and so forth. Births with an interval of zero months are excluded from the computation of mean intervals. Educational attainment clsnat85.doc - Page 6 Data on the educational attainment of both parents were collected beginning in 1968 and tabulated for publication in 1969 for the first time. In 1985, data on education were obtained from 47 States and the District of Columbia, as indicated in table A. The educational attainment of either parent is defined as "the number of years of school completed." Only those years completed in "regular" schools, that is, a formal educational system of public schools or the equivalent in accredited private or parochial schools, are counted. Business or trade schools, such as beauty and barber schools, are not considered "regular" schools for the purposes of this item. No attempt has been made to convert years of school completed in foreign school systems, ungraded school systems, and so forth to the equivalent grade in the American school system. Such entries are included in the category "Not stated." Persons who have completed only a partial year in high school or college are tabulated as having completed the highest preceding grade. For those certificates on which a specific degree is stated, years of school completed is coded to the level at which the degree is most commonly attained: for example, persons reporting B.A., A.B., or B.S. degrees are considered to have completed 16 years of school. Education not stated-The category "Not stated" includes all records in reporting areas for which there is no information on years of school completed as well as all records for which the information provided is not compatible with coding specifications. Births tabulated as education not stated are excluded from the computations of percents. Marital status Beginning with 1980 data, national estimates of births to unmarried women are derived from two sources. For 41 States and the District of Columbia, marital status of the mother was reported directly on the birth certificate in 1985 (see table A); for the remaining 9 States that lack this item, marital status was inferred from a comparison of the child's and parent's surnames. This procedure represents a substantial departure from the previous method used to prepare national estimates, which assumed that the incidence of births to unmarried women in States with no direct question on marital status was the same as the incidence in reporting States in the same geographic division. Ratios of births to unmarried women were computed by race for the reporting States in each geographic division, applied to all births in the division, and then summed to obtain national estimates by race. The figures by race were summed to yield the totals for the United States. The new method attempts to use related information on the birth certificate to improve the quality of national data on this topic, as well as to provide data for the individual nonreporting States. Beginning in 1980, a birth in a nonreporting State is classified as occurring to a married woman if the parents' surnames are the same or if the child's and father's surnames are the same and the mother's current surname cannot by obtained from the informant item of the birth certificate. A birth is classified as occurring to an unmarried woman if the father's name is missing, if the parents' surnames are different, or if the father's and child's surnames are different and the mother's current surname is missing. clsnat85.doc - Page 7 Table A. Areas reporting selected items on the live-birth certificate: Table A Each State, 1985 Dates of last live Area Educational birth and Number of Marital 1-minute 5-minute Ethnic Hispan attainment last prenatal status Apgar Apgar origin -ic of parents other visits of mother score score origin termination Alabama x x x x x x Alaska x x x x x x Arizona x x x x x x x Arkansas x x x x x x x California x x Colorado x x x x x x x Connect x x x x x -icut Delaware x x x x District x x x x x x x of Columbia Florida x x x x x x x Georgia x x x x x x x Hawaii x x x x x x x Idaho x x x x x x Illinois x x x x x x x Indiana x x x x x x x Iowa x x x x x x Kansas x x x x x x x Kentucky x x x x x x Louisiana x x x x x x Maine x x x x x x x Maryland x x x x x Massachu x x x x x x -setts Michigan x x x x x Minnesota x x x x x x Mississ x x x x x x x -ippi Missouri x x x x x x Montana x x x x x Nebraska x x x x x x x Nevada x x x x x x New Hamp x x x x x x -shire New Jersey x x x x x x x New Mexico x x x x x x x New York x x x x x x1 x2 North Ca x x x x x x -rolina North Da x x x x x x x -kota Ohio x x x x x x Oklahoma x x x x clsnat85.doc - Page 8 Oregon x x x x x x Pennsylvan x x x x x x -ia Rhode Is x x x x x x -land South Ca x x x x x x rolina South Da x x x x x x -kota Tennessee x x x x x x x Texas x x Utah x x x x x x x Vermont x x x x x x Virginia x x x x x x Washington x x x x x West Vir x x x x x x -ginia Wisconsin x x x x x x Wyoming x x x x x x x 1 New York City only. 2 Excludes New York City. Because of the substantial increase in all measures of nonmarital childbearing in 1985, the intensive evaluation of the national data was made. There has been continuing concern that the current method, incorporating data based on a comparison of surnames, might overstate the number of births to unmarried women, particularly among women who retained their maiden name as their legal surname after marriage. The evaluation included comparisons of trends in all measures of births to unmarried mothers between 1980, when the new method was first put into use, and 1985. Trends in the States with a marital status item on the birth certificate were compared with trends in those States providing inferential data based on a comparison of surnames. Comparisons were made for white and black births separately and by age of mother. The results were remarkably similar for both data sets. Nonmarital births increased at virtually the same rate in each set of States. The findings were similar for white and black women and for the various age-of-mother groups. No adjustments are made during the data processing for errors in the reporting of marital status on the birth records of the 41 reporting States and the District of Columbia because the extent of this reporting problem is unknown. When marital status is not stated on the birth certificate of a reporting area, the mother is considered married. When births to unmarried women are reported as second or higher order births, it is not known whether the mother was previously married or unmarried when the deliveries occurred, because her marital status at the time of these earlier births is not available from the birth record. Rates for 1940 and 1950 are based on decennial census counts. In this volume, rates for 1955-85 are based on a smoothed series of population estimates (NCHS, 1980). Because of sampling error, the original U.S. Bureau of the Census population estimates fluctuate erratically from year to year; therefore, they have been smoothed so that the rates do no show similar variations. The rates shown in this volume differ from those published in issues of Vital Statistics of the United States before 1969, which were based clsnat85.doc - Page 9 on the original estimates provided annually by the U.S. Bureau of the Census. Birth rates by marital status for 1971-79 have been revised and differ from rates published before 1980 in issues of Vital Statistics of the United States see "Computation of rates and other measures"). Place of delivery and attendant at birth Births occurring in hospitals, institutions, clinics, centers, or homes are included in the category "In hospital." In this context the word "homes" does not refer to the mother's residence but to an institution, such as a home for unwed mothers. Beginning in 1975, the attendant at birth and place of delivery items were coded independently, primarily to permit the identification of the person in attendance at hospital deliveries. Tables 1-37 and 1-38 of this report present this more detailed information for the years 1975-85. Data shown in this volume for the "In hospital" category for the years 1975-85 include all births in clinics or maternity centers, regardless of the attendant. Data for 1975-77 published before 1980 included clinic and center births in the category "In hospital" only when the attendant was a physician. Data shown for 1975-77 in tables 1-37 and 1-38, therefore, differ from data published before 1980. As a result of this change, for 1975 an additional 12,352 births are now classified as occurring in hospitals, raising the percent of births occurring in hospitals from 98.7 to 99.1 percent. Similarly, for 1976 the number of births occurring in hospitals is increased by 14,133 and the percent in hospitals raised from 98.6 to 99.1 percent; for 1977, the increase is 15,937 and the percent in hospitals raised from 98.5 to 99.0 percent. For 1974 and earlier, the "In hospital" category includes all births in hospitals or institutions and births in clinics, centers, or maternity homes only when attended by physicians. For births occurring outside of hospitals, separate classifications are shown for physicians, midwives, and "Other" attendants. The "Out-of-hospital" category also includes births for which no information is reported on place of birth. Before 1975, the category "In hospital" included births for which the stated place of birth was a "doctor's office" and delivery was by a physician. Beginning in 1975, births that were delivered by physicians in a "doctor's office" were tabulated as "Not in hospital" and included with births delivered by physicians in this category. Although the actual number of such births is unknown, the effect of the change is minimal. In 1974, 0.3 percent of all births were delivered by physicians outside of hospitals; in 1975 this proportion was 0.4 percent. Babies born on the way to or on arrival at the hospital are classified as having been born in the hospital. This may account for some of the hospital births not delivered by physicians or midwives. The percent distributions by attendant at birth for 1975-81 shown in table 1-38 have been revised to exclude births for which the attendant was unspecified. In recent years, the number of births with unspecified attendant has fluctuated substantially. Excluding these births from the percent distributions allows for a more meaningful year-to-year comparison in the proportion of births for each specified attendant. Birth weight Birth weight is reported in some areas in pounds and ounces rather than clsnat85.doc - Page 10 in grams. However, the metric system has been used in tabulating and presenting the statistics to facilitate comparison with data published by other groups. The categories for birth weight were changed in 1979 to be consistent with the recommendations in the Ninth Revision of the International Classification of Diseases (ICD-9). The revised categories in gram intervals and their equivalents in pounds and ounces are as follows. Less than 500 grams = 1 lb 1 oz or less 500 - 999 grams = 1 lb 2 oz - 2 lb 3 oz 1,000 - 1,499 grams = 2 lb 4 oz - 3 lb 4 oz 1,500 - 1,999 grams = 3 lb 5 oz - 4 lb 6 oz 2,000 - 2,499 grams = 4 lb 7 oz - 5 lb 8 oz 2,500 - 2,999 grams = 5 lb 9 oz - 6 lb 9 oz 3,000 - 3,499 grams = 6 lb 10 oz - 7 lb 11 oz 3,500 - 3,999 grams = 7 lb 12 oz - 8 lb 13 oz 4,000 - 4,499 grams = 8 lb 14 oz - 9 lb 13 oz 4,500 - 4,999 grams = 9 lb 15 oz - 11 lb 0 oz 5,000 grams or more = 11 lb 1 oz or more The ICD-9 defines low birth weight as less than 2,500 grams. This is a shift of 1 gram from the previous criterion of 2,500 grams or less, which was recommended by the American Academy of Pediatrics in 1935 and adopted by the World Health Organization in the Sixth Revision of the International Lists of Diseases and Causes of Death. After data classified by pounds and ounces are converted to grams, median weights are computed and rounded before publication. To establish the continuity of class intervals needed to convert pounds and ounces to grams, the end points of these intervals are assumed to be half an ounce less at the lower end and half an ounce more at the upper end. For example, 2 lb 4 oz - 3 lb 4 oz is interpreted as 1 lb 3 1/2 oz - 3 lb 4 1/2 oz. Births for which birth weight is not reported are excluded from the computation of percents and medians. Period of gestation The period of gestation is defined as beginning with the first day of the last normal menstrual period (LMP) and ending with the day of the birth. The LMP is used as the initial date because it can be more accurately determined than the date of conception, which usually occurs 2 weeks after the LMP. Births occurring before 37 weeks of gestation are considered "preterm" or "premature" for purposes of classification. At 37-41 weeks' gestation, births are considered "term," and at 42 weeks and over, "postterm." These distinctions are according to the ICD-9 definition. Before 1981, the period of gestation was computed only when there was a valid month, day, and year of LMP. However, length of gestation could not be determined from a substantial number of live birth certificates each year because the day of LMP was missing. Beginning in 1981 weeks of gestation have been imputed for records with missing day of LMP when there is a valid month and year. Each such record is assigned the gestational period in weeks of the preceding record that has a complete LMP date with the same computed months of gestation and the same 500-gram birth weight interval. The effect of the imputation procedure is to increase slightly the proportion of premature births and to lower the proportion of births at 39,40, 41, and 42 weeks of clsnat85.doc - Page 11 gestation. A more complete discussion of this procedure and its implication is presented in a previous report (NCHS, 1982). The calculated period of gestation in completed weeks is edited for upper and lower limits. If the interval between date of LMP and date of birth is 16 weeks or less, or 53 weeks or more, the period of gestation is considered not stated. Because of post-conception bleeding or menstrual irregularities, the presumed date of LMP may be in error. In these instances the computed gestational period may be longer or shorter than the true gestational period, but the extent of such errors is unknown. Month of pregnancy prenatal care began For those records in which the name of the month is entered for this item, instead of first, second, third, and so forth, the month of pregnancy in which prenatal care began is determined from the month named and the month last normal menses began. For these births, if the item "Date last normal menses began" is not stated, the month of pregnancy in which prenatal care began is tabulated as not stated. Number of prenatal visits Tabulations of the number of prenatal visits were presented for the first time in 1972. In 1985 these data were collected from the birth certificates of all States except California. Apgar score One- and 5-minute Apgar scores were added to the U.S. Standard Certificate of Live Birth in 1978 to evaluate the condition of the newborn infant at 1 and 5 minutes after birth. The Apgar score is a useful measure of the need for resuscitation and a predictor of the infant's chances of surviving the first year of life. It is a summary measure of the infant's condition based on heart rate, respiratory effort, muscle tone, reflex irritability, and color. Each of these factors is given a score of 0, 1, or 2; the sum of these values is the Apgar score, which ranges from 0 to 10. A score of 10 is optimum, and a low score raises some doubts about the survival and subsequent health of the infant. In 1985 the 1- and 5-minute Apgar scores were included on the birth certificates of 46 States and the District of Columbia. See table A for a listing of reporting areas. Hispanic parentage Concurrent with the 1978 revision of the U.S. Standard Certificate of Live Birth, the National Center for Health Statistics recommended that States add items to identify the Hispanic or ethnic origin of the newborn's parents. Two formats were used: (1) an open-ended item to obtain the specific origin or descent or each parent, for example, Italian, Mexican, or English; and (2) an item directed toward the Hispanic population, requesting only the specific Hispanic origin (Mexican, Puerto Rican, Cuban, and so forth). In 1985 items requesting Hispanic or ethnic origin were included on the birth certificates of 23 States and the District of Columbia (see table A). clsnat85.doc - Page 12 clsnat85.doc - Page 13