The graph presents, in the form of bars, the total number of births annually from 1933 through 2000. These births are then charted as a percentage of total births by the age of the mother. The left side of the graph depicts an era before reliable birth control methods were available. The mid-1940s are a particularly volatile period as the impact of U.S. participation in World War II had a notable impact on birth rates.
The right side of the graph presents data for a period in which birth control was readily available and women were entering college and the workforce in record numbers.
The trend towards postponing childbearing until later in life is clearly visible in this graph. The higher age groups all grew in terms of their percentage of births. The younger age groups bore a smaller percentage of the babies born as we neared the turn of the century. The age group 20 to 24 has been surpassed by those aged 25 to 29. Women in there early 30s accounted for 23% of births in 2000, almost as many as the women in their early 20s who bore 25% of the babies. Women in their late 30s accounted for almost as many births (11.1%) in 2000 as women in their late teens (11.6%), an age group that has seen its percentage of births drop sharply from a high of 19.3% in 1973.
In part this birth pattern results from the dominance of the Baby Boom in all late 20th century demographic trends. There were, quite simply, more women in their 30s in the 1990s than women in their 20s.
Female Population Figures by Age Group
(2005 and 2010 are projections)
| Women in their: | 1970 | 1980 | 1990 | 2000 | 2005 | 2010 |
| 20s | 15,309,000 | 20,595,000 | 19,967,000 | 18,017,000 | 18,830,000 | 19,433,000 |
| 30s | 11,829,000 | 16,290,000 | 21,086,000 | 20,977,000 | 18,745,000 | 18,017,000 |
The trend towards childbearing later in life results from both demographic realities as well as social, cultural, and economic changes. The age at which men and women enter a first marriage has also risen during the 20th century as we have delayed the commitment to marriage and family-formation generally4. The question is, will this trend continue, stabilize? Or, alternately, will it prove to have been another Baby Boom-related trend that will reverse itself as the boom generation ages?
Only time will tell. During the first decade of the 21st century the youngest of the Baby Boom generation will pass out of the breeding age range, and we will then see whether the pattern they have set, of childbearing later in life, continues. Worth noting is the fact that during this same period women in their 20s will again out-number women in their 30s.
Next we turn to two trends that have emerged in the 1990s and are at least tangentially related to later childbearing: the rise in multiple birth pregnancies (twins, triplets, quad- ruplets, etc…) and the rise in cesarean deliveries.
Source: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics, Division of Vital Statistics, "Live Births by Age of Mother and Race: United States, 1933-98. For the years 1999 and 2000, and published by the same department "Births: Final Data for 2000" issued on February 12, 2002. Population by age group data is from two U.S. Census Bureau publications, Historical Statistics of the United States, Colonial Times to 1970, page 15, and Statistical Abstract of the United State: 2001, pages 14 and 15. Data on median age at first marriage are from the U.S. Census Bureau, Current Population Report, "American Families and Living Arrangements: March 2000" and "Census 2000 Supplemental Survey Profile," table 1.
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