Maternal age at childbirth is an important determinant of the health of the mother and child. Birth registration data--reported by states and the District of Columbia to CDC's National Center for Health Statistics--provide demographic and health information on mothers and their babies and permit examination of age-related trends in childbearing.

The annual birth rate for women aged 30-34 years declined from 73 per 1000 women in 1970 to 52 per 1000 in 1975, but rose to 71 per 1000 in 1987 (1) (Table 1). Rates for women in the peak childbearing years (20-29) remained generally stable during 1975-1987.

A large proportion of the overall increase in birth rate for women aged 30-34 years is attributable to an increase in the rate of first births, which more than doubled (from 8.0 to 18.4 first births per 1000 women) between 1975 and 1987 (Figure 1). In contrast, the rate of first births for women aged 20-24 years ranged from 52.4 to 57.3 over this period.

The distribution and number of first births among women aged greater than or equal to 30 years have also changed dramatically. In 1970, 4% of women having their first child were aged greater than or equal to 30 years, compared with 16% in 1987 (1,2). The number of first births to women aged greater than or equal to 30 years increased from 56,728 in 1970 to 250,304 in 1987. Reported by: Div of Vital Statistics, National Center for Health Statistics, CDC.

Editorial Note

Editorial Note: Several demographic, social, and economic factors appear to be associated with this trend toward later childbearing. From 1946 to 1964, children were born at record high rates in the United States. As a result, between 1970 and 1987, the number of women aged 30-44 years increased by 59% (from 17.7 million to 28.1 million) (3,4). Concomitantly, the proportion of women who were childless when they reached 30 years of age increased from 15% in 1970 to 31% in 1987. As a result, an unprecedented number of women were "at risk" for a first birth in later childbearing years. Approximately half of childless women aged 30-34 years intend to have at least one child (5).

Women aged greater than or equal to 30 years experiencing their first childbirth in 1987 had several characteristics with important positive consequences for health. Nearly half (49%) were college graduates, compared with 19% of first-time mothers in their 20s (6). Eleven percent were unmarried when their child was born, compared with 22% of first-time mothers in their 20s. More than two thirds were employed, and 91% received prenatal care beginning in the first trimester. In addition, well-educated women are more likely to have good diets, gain adequate weight during pregnancy, and be nonsmokers (7-9).

The trend in postponed childbearing is likely to continue. The proportion of college graduates among women aged 30-34 years increased between 1975 (16%) and 1987 (24%), and these women are marrying at older ages (10). Therefore, women in their 30s of higher socioeconomic status will likely account for an increasing proportion of first births.

References

1. NCHS. Advance report of final natality statistics, 1987.

Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, 1989. (Monthly vital statistics report; vol 38, no. 3, suppl).

2. Ventura SJ. Trends and variations in first births to older women, 1970-86. Vital Health Stat 1989;21(47).

3. Bureau of the Census. Preliminary estimates of the population of the United States, by age, sex, and race: 1970 to 1981. Washington, DC: US Department of Commerce, Bureau of the Census, 1982. (Current population reports; series P-25, no. 917).

4. Bureau of the Census. Estimates of the population of the United States, by age, sex, and race, 1980 to 1987. Washington, DC: US Department of Commerce, Bureau of the Census, 1988. (Current population reports; series P-25, no. 1022).

5. Bureau of the Census. Fertility of American women: June 1987. Washington, DC: US Department of Commerce, Bureau of the Census, 1988. (Current population reports; series P-20, no. 427).

6. Bureau of the Census. Educational attainment in the United States, March 1987 and 1986. Washington, DC: US Department of Commerce, Bureau of the Census, 1988. (Current population reports; series P-20, no. 428). 7. Taffel S. Maternal weight gain and the outcome of pregnancy, United States, 1980. Vital Health Stat 1986;21(44).

8. Prager K, Malin H, Spiegler D, Van Natta P, Placek P. Smoking and drinking behavior before and during pregnancy of married mothers of live-born infants and stillborn infants. Public Health Rep 1984;99:117-27.

9. Mosher W, Pratt W. Fecundity, infertility, and reproductive health in the United States, 1982. Vital Health Stat 1987;23(14). 10. NCHS. Advance report of final marriage statistics, 1986. Hyattsville, Maryland: US Department of Health and Human Services, Public Health Service, 1989. (Monthly vital statistics report; vol 38, no. 3, suppl 2).

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