Forecasts show many millennial women won’t fulfill their wishes on family size, and the biggest fertility declines are in Western states.

America’s fertility is in precipitous decline. Our team of forecasters at Demographic Intelligence projects 3.84 million births in 2017, down from about 3.95 million in 2016.

And it’s likely to fall further — far short of what women themselves say they want for their family size.

The latest data from the Centers for Disease Control and Prevention, reflecting births as of the year ending in September 2017, shows the total fertility rate at 1.77 lifetime births per woman, down 3.8 percent since 2015, and down 16.4 percent since its most recent peak at 2.12 in 2007. (The replacement rate in developed countries is around 2.1.)



The total fertility rate is a measure of how many children a woman entering her reproductive years today could expect to have, if age-specific fertility rates remain constant over time.

In other words, it’s a very simplistic forecast of lifetime births. But there is a lot that the available data can reveal.

The fertility rate has increased for women over 40, and the generation of women finishing up their childbearing years now had more children than their mothers did, but that isn’t likely to be true for their daughters. The key factors driving down the birthrate are not mysterious: The pregnancy rate among young women is falling, and has been for years.

But what began as sharp declines in pregnancy and childbearing among teenagers — typically considered a socially desirable result — has slowly spread up the age cohorts, first to women in their early 20s, then to those in their late 20s. And now fertility decline has set in for women even in their 30s. Far from reversing as America grew out of economic recession, this lost fertility has worsened.



A key factor is that marriage is increasingly being postponed. Total fertility rates controlling for marital status have not changed very much over the last 15 years. But with marriage coming later, the share of women at peak childbearing ages (20 to 40) who are married has steadily fallen.

As millennials in particular take their time to pair up, the average age of first birth is rising steadily. Today, the average age of a woman at first birth is over 26 years old. And while that is much higher than in the past, many European countries have an average age of first birth over 30, so there seems a lot more room to rise. In fact, the United States has the youngest age of first childbirth of any developed country.

Beyond delayed marriage, unmarried births are falling, too. Wider usage of long-acting reversible contraceptives (LARCs) is especially helping unmarried women avoid unintended pregnancy (from 1.5 percent LARC usage in 2002 to 7.2 percent in 2011-2013).

And the increasing availability and usage of emergency contraceptives (which some consider to be abortions but are not counted in official abortion statistics) further reduces the likelihood of implantation (from 1 percent emergency contraceptive usage in 1995 to 11 percent in 2006-2010).

But while most everyone can agree that reducing unintended pregnancy is a good thing, there have been relatively few innovations in technology or social structure to enable desired parenting.

Technologies such as in vitro fertilization, ovulation-enhancing medicines, egg storage and artificial insemination have been around for decades now, and remain extremely expensive in many cases. A single attempt of even a very simple assisted-conception procedure can cost thousands of dollars, with even higher costs for more involved procedures, often not covered by insurance.

Meanwhile, the share of the childless population assisting in parenting and child care is in steady decline. (The data show that many parents are overwhelmed, and assists from friends and family can be helpful.) Americans are improving their ability to avoid unwanted pregnancies far faster than they are improving the ability to achieve desired pregnancy.



As a result, the gap between the number of children that women say they want to have (2.7) and the number of children they will probably actually have (1.8) has risen to the highest level in 40 years. (From 1972 to 2016, men have expressed almost exactly the same ideal fertility rates as women: In a given year, they average just 0.04 children below what women say is ideal.)

Sometimes, it’s the little things that drive these trends. For example, Americans across many ages and marital statuses are having less sex than they used to.

Data from the General Social Survey shows that the share of people 18 to 30 who have not had sex in the past year has risen to nearly 20 percent today, from about 10 percent between 1990 and 2010, while the share having sex at least two times a month has fallen to about 65 percent, from about 75 percent from 1990 to 2010.

Diminished face-to-face interaction, and possibly increased use of pornography, may explain the fall in sex, and both of those trends may be explained by the rise in cellphone usage and other screen time.

Smartphone ownership rates have more than doubled for every age group in America since 2010, meaning that almost all of us now carry a get-out-of-human-interaction-free card in our pockets 24/7.



But these are all long-term trends. What’s driving the decline right now?

Answering that question may be more about where than what. Using census population estimates by sex and age for states and making some simple extrapolations to monthly data, we can make a reasonable guess of where birthrates per-childbearing-age-woman are falling or rising most. The map below shows an estimate of the change in the share of childbearing-age-women who had a birth in the previous year, which demographers call the general fertility rate.

As you can see, the steepest declines have been in Western states, especially previously high fertility states like Utah. Only Alabama and Connecticut have posted any likely increase in their general fertility rate over the last three years. Connecticut’s fertility rate has been roughly tied for lowest in the nation for several years, however, so a small gain isn’t saying much. Alabama’s increase is more interesting, but peaked in late 2015 and has been declining since.

As millennials slowly begin to transition toward marriage and homeownership, children may come, too. But it’s unlikely any future baby boom will be able to fully offset the baby bust of the last 10 years. Many will cheer this development, pointing to overpopulation and the stress put on the environment. But very real problems could develop from lower fertility that many might not see coming, like difficulty meeting Social Security obligations, caring for older people and maintaining economic growth.

Regardless of your view, millennial women are likely to experience the largest shortfall in achieved fertility versus their stated family desires of any generation in a long time, unless something changes soon.

Lyman Stone is an economist who writes about demographics and population economics. He is an adviser at Demographic Intelligence, and does commodity analysis in the Department of Agriculture. He blogs at In a State of Migration, and you can follow him on Twitter at @lymanstoneky.

A version of this article appears in print on , on Page A14 of the New York edition with the headline: Decline in Fertility, Below Even What Young Women Say They Want. Order Reprints | Today’s Paper | Subscribe