Infants born to teenaged mothers and to unmarried mothers are particularly at risk for low birth weight (LBW), which in turn increases their risk for serious morbidity, permanent disability, and death. In the United States, data from birth certificates are the primary source for monitoring trends in reproductive patterns and maternal and infant health. This report uses information from U.S. birth certificates for 1980 and for 1985--1988 to characterize trends in fertility among teenagers (aged 15--19 years) and unmarried women, use of prenatal care, and the incidence of LBW.

Birth rates for teenagers changed little from 1980 through 1985 (1) (Table 1). However, from 1986 through 1988, the overall rate for women aged 15--19 years increased 6%, from 50.6 to 53.6 births per 1000, and for women aged 15--17 years, 10%.

In 1988, more than 1 million infants were born to unmarried mothers, accounting for 26% of all infants (Table 2) (18% of white infants, 63% of black infants, and 34% of Hispanic infants); these percentages reflected increasing trends for 1980--1988. For unmarried women aged 15--44 years, the birth rate was 38.6 per 1000. Although rates of childbearing among unmarried women remained highest among black women, during the 1980s the increases were greater for white women---from 1980 through 1988, a 51% increase for white women (from 17.6 to 26.6 per 1000, respectively) compared with 7% for black women (from 82.9 to 88.9 per 1000, respectively).

From 1980 through 1988, the proportion of all mothers who received prenatal care during the first trimester of pregnancy remained constant (76%) (Table 3). For white mothers, increases in early prenatal care occurred for both married and unmarried women, although the increase was more prominent for unmarried mothers (Table 3). Since 1980, however, the proportions of mothers who did not receive prenatal care until the third trimester or who received no prenatal care increased for both white and black women (1,2).

The receipt of early prenatal care was associated with a decreased risk for LBW infants ( less than 5 lbs 8 oz (2500 g)) (3,4). From 1980 through 1988, the percentage of LBW infants was essentially stable. In 1988, for white mothers who had full-term infants, the percentage of LBW infants was 2.2% for women who initiated care in the first trimester; 3.4%, the second trimester; 3.9%, the third trimester; and 7.8%, for those who received no prenatal care. In comparison, for black mothers who had full-term infants, the proportions of LBW infants were 5.2% for women who initiated care in the first trimester; 6.3%, the second trimester; 6.6%, the third trimester; and 13.3%, for those who received no prenatal care.

From 1981 through 1988, the proportion of preterm births increased from 9.4% to 10.2%. In 1988, nearly 40% of preterm infants had LBW, compared with 2%--3% for full-term and postterm infants. Black mothers were more likely to have a preterm infant than were white mothers (18.3% vs. 8.5%). Reported by: Div of Vital Statistics, National Center for Health Statistics, CDC.

Editorial Note

Editorial Note:

The findings in this report indicate an increase in birth rates for teenagers during the 1980s, which may reflect either an increase in their pregnancy rate or a decline in the abortion rate. However, a previous report indicated that during the 1980s the abortion rate for teenagers changed minimally (5), suggesting that the increased birth rate from 1986 through 1988 represented an increase in the pregnancy rate. Data from the National Survey of Family Growth, conducted by CDC's National Center for Health Statistics, indicate that during the 1980s the proportion of teenaged women who had had sexual intercourse increased substantially. For those aged 15--19 years, the proportion increased from 42% in 1980 to 52% in 1988 (6), and increases were greater among younger teenagers.

The increase in births to unmarried women during the 1980s reflected the substantial growth in the population of unmarried women of childbearing age and in birth rates for unmarried women. Although increased rates occurred for women in all age groups, they were greatest for women aged 25--39 years, the age group characterized by the greatest population increases (7). In 1988, women greater than or equal to 25 years of age accounted for nearly 33% of all births to unmarried women. However, the absolute birth rates continued to be highest for women aged 18--24 years (Table 2). Infants born to teenagers and to unmarried mothers (many of whom are teenagers) are at high risk for poor outcomes because of factors affecting maternal health, including low socioeconomic status, inadequate nutrition, and poor access to health care.

The increasing difference in LBW infants born to white and black women has been attributed, in part, to the increasing proportion of black mothers in groups at high risk for LBW (i.e., women less than 20 years of age, with less than 12 years of education, or with late or no prenatal care) (4). The increased number of LBW infants also reflects the increasing number of births to unmarried white and black mothers and to mothers receiving late or no prenatal care.

The findings in this report underscore the need to focus prenatal-care programs on women least likely to receive timely prenatal care and those at greatest risk for having a LBW infant. Providing prenatal care services to these mothers should substantially reduce the social and economic costs of caring for LBW infants at greatest risk for illness, long-term disability, and death (4,8,9).

References

1. NCHS. Advance report of final natality statistics, 1988. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1990. (Monthly vital statistics report; vol 39, no. 4, suppl).

2. NCHS. Advance report of final natality statistics, 1987. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC 1989. (Monthly vital statistics report; vol 38, no. 3, suppl).

3. Taffel SM, NCHS. Trends in low birth weight: United States, 1975--85. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, CDC, 1989. (Vital health statistics; vol 21, no. 48).

4. Institute of Medicine. Preventing low birthweight. Washington, DC: National Academy Press, 1985.

5. Henshaw SM, Koonin LM, Smith JC. Characteristics of U.S. women having abortions, 1987. Fam Plann Perspect 1991;23(2).

6. CDC. Premarital sexual experience among adolescent women---United States, 1970--1988. MMWR 1991;39:929--32.

7. Bureau of the Census. United States population estimates, by age, sex, race, and Hispanic origin, 1980 to 1988. Washington, DC: US Department of Commerce, Bureau of the Census, 1990.

8. Hughes D, Johnson K, Rosenbaum S, et al. The health of America's children: maternal and child health data book. Washington, DC: Children's Defense Fund, 1988.

9. Miller CA. Fine A, Adams-Taylor S. Monitoring children's health: key indicators. 2nd ed. Washington, DC: American Public Health Association, 1989.

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