Low birthweight and very low birthweight are expressed as the percentage of live births weighing less than 2,500 grams and 1,500 grams, respectively. The major source of data on low birthweight and very low birthweight is the birth certificate. Information from birth records is sent by the states to NCHS. The 1988 NMIHS (National Center for Health Statistics, 1991) provides more detailed information about the extent of prenatal care and risk factors associated with low birthweight and very low birthweight.
Additional understanding of the low birthweight problem should be possible when 1989 birth certificate data become available for analysis. The revised birth certificate includes information on medical risk factors and maternal behavior during pregnancy (tobacco and alcohol use) as well as low maternal weight gain—all factors that have been associated with low birthweight.
Efforts to monitor changes in low birthweight are hindered by the considerable time lag between data collection and publication. Similar delays are present in the availability of national linked birth and death certificate data, which are the best source for determining the relationship between low birthweight and poor health outcomes (Miller et al., 1989). In addition, as is true for all events dependent on birth records, no data are available on the source of payment for care.
Table 3-7 displays the percentage of infants of low birthweight by race in the United States for selected years from 1970 through 1988, the last year for which data are available. What is most striking is how little change there has been over time. Although there was some decline in low birthweight births during the 1970s, no improvement was apparent during the 1980s. The percentage of low birthweight black infants also deserves note. The ratio of black to white low birthweight births in 1970 was 2.04. A slow but steady increase in the disparity has occurred over the past 20 years, until by 1988 the ratio reached 2.32. The percentage of low birthweight babies born to nonwhites in 1988 was the same as in 1976. Table 3-8 shows low birthweight births for 1988 by racial and ethnic groups. Unlike the previous table, these data are based on the race/ethnicity of the mother rather than the infant.
Table 3-8 reveals the heterogeneity of the Hispanic population. The percentage of low birthweight infants varies from 5.6 per 1,000 live births for Mexican American and Central and South American women to 9.4 per 1,000 live births for Puerto Rican women. The incidence of low birthweight among Puerto Ricans was approximately two-thirds higher than that of white women.