FERTILITY is rising in the United States, with potentially profound consequences. This year, for the first time in decades, the total fertility rate in the US could reach 2.1 births per female. That is the rate at which a population exactly replaces itself.
The foremost impact of higher fertility will be on Social Security, demographers agree. ``We're generating more future workers whose paychecks will be taxed to support you and me when we're collecting our Social Security benefits,'' says Peter Morrison, a demographer at RAND Corporation's Population Research Center.
Other factors affected by a higher fertility rate range from more crowded classrooms to a stronger market for maternity fashions for pregnant women to a boost in business for toy manufacturers.
Reaching the 2.1 ``replacement'' level is ``conceivable, definitely,'' says Stephanie Ventura, a demographer at the National Center for Health Statistics who has a reputation for caution. Recently a rumor has been circulating among population-watchers that a jump to 2.1 has just been announced by the NCHS, which tracks fertility statistics.
Actually, NCHS has data only through August for this year, and 1989 data are still considered provisional. Nonetheless, a rise to 2.1 for 1990 would be consistent with the trend in most fertility measurements.
An exception is the Census Bureau's chart of actual completed fertility, a figure that can differ greatly from estimates of fertility for all women. This statistic looks at women age 40-44, considered to be at the end of their reproductive years, and tallies how many times they gave birth. It declined from 3.0 in 1980 to 2.1 in 1988.
Even though actual completed fertility is a look backward, confirming a previously recognized pattern for that age group, ``we don't expect an upward trend,'' says Amara Bachu, a statistician-demographer with the Census Bureau's fertility statistics branch.
Ms. Bachu cites current bureau surveys that inquired about childbearing intentions. ``American women know pretty well what they want. They say they will have two children, and they do.''
In the past, the bureau has consistently underestimated fertility upswings and overestimated the downswings, according to Dennis Ahlburg and James Vaupel at the University of Minnesota.
In the November issue of Demography, they make a case for growth scenarios that give the US a population of as much as 811 million by 2080. The Census Bureau's high-case projection for that year is 501 million.
It's exciting enough to some demographers that fertility in the US isn't declining. ``The question in the air was whether it was going to keep going down to 1.4 or 1.5, stay where it was, or rebound. The risk that we're on the downside seems to be disappearing,'' says Alicia Munnell, director of research at the Federal Reserve Bank of Boston.
``There are many people who have adopted the view that fertility is about as low as it will ever go in the United States,'' says Dr. Morrison. But he isn't one of them, he adds.
Morrison would like to see the higher fertility rate continue for a few years before admitting that ``it's anything more than an unexplainable hiccup.'' But he concedes that it may be a trend.
The rise in the fertility rate appears to be manifested by nearly every age group in the 15-44 range.
Ms. Ventura highlights the impact on total fertility caused by baby-boomers. They are great in number and are now having long-postponed births. Fertility among women 25 and older has been increasing for several years at 7 to 8 percent a year, she says.
But will they have as many children as they would have if they had started younger? ``They probably won't,'' she says.
Another key bracket is the 20- to 24-year-olds, who remain the most fertile. ``If it's true that the birthrate is going up to 2.1, then it's hard to believe it could be other than women in their 20s, because those women are the ones who dominate the birthrate,'' says Richard Easterlin, a professor at the University of Southern California.
Social Security will be most affected if fertility rates increase, demographers say. ``It significantly reduces the cost to the system over the long run, providing that fertility rates stay at this high level,'' says Robert Ball, a former commissioner of the Social Security Administration.
But a conversation with that agency reveals that the potential impact of a higher fertility rate may be exaggerated. Today, 3.4 workers pay into the system for each beneficiary drawing money out. That ratio will fall to two workers per beneficiary by 2030, based on Social Security's current assumptions about fertility: a 1.92 rate in 2000, 1.91 by 2005, and 1.90 from 2015 to 2065.
Taxes paid in currently total $294 billion, and withdrawals $248 billion. The difference is added to a reserve that has reached $225 billion. ``You're partially funding some of your future benefits,'' even though that's not how the system was supposed to work, says Phil Gambino, chief spokesman of the Social Security Administration.
By 2025 this reserve will grow in current (inflation-diluted) dollars to $9.2 trillion. Yet by 2045 Social Security will be broke. He considers it a feat that the system could operate as is, with no planned changes in taxes or benefits, until 2045 without collapsing.
So how much difference would a higher birthrate help? A steady 2.0 would delay bankruptcy four years, he says. A second and third tenth of a percent would add five and six years, respectively.
But even that rate might be low. Professors Ahlburg and Vaupel, in their Demography article, advance the possibility of a total fertility rate of 2.7 to 3.2 during further baby booms peaking in 2005, 2030, 2055, and so on. That's a lower rate than the 3.6 to 3.8 that prevailed from 1956-61, they note.
Whatever the case, fertility is only one of a dozen variables affecting Social Security. The unemployment rate, wage levels, growth in gross national product, growth in jobs - ``those things really tremendously affect the program,'' Gambino says.