(Mike Derer/AP)

Imagine that all women in the United States, upon becoming sexually active, were automatically fitted with an intrauterine device or other form of long-acting birth control. This scenario sounds creepy, with its undertones of Big Brother and eugenics; framed this way, it would be neither a realistic nor a desirable development.

But this thought experiment, provoked by a new book by Brookings Institution scholar Isabel Sawhill, illuminates two important societal and technological realities.

First, as Sawhill describes in “Generation Unbound: Drifting into Sex and Parenthood Without Marriage,” single parenthood is becoming the unhealthy “new normal.” Once, single parenthood was the consequence of divorce or the province of the poorest and least educated.

Now, divorce rates are edging down. The prevalence of single parenting is largely a function of the never-married. The average woman today has her first baby before she is married. Meanwhile, single parenthood is invading the ranks of the middle class, often involving children with multiple partners.

The stereotypical single mother used to be a high school dropout. No more. In 2010, Sawhill notes, 58 percent of first births to those with high school diplomas or some college were out of wedlock. (The comparable figure for those with a college degree was just 12 percent.)

The paradox of the growing rate of single parenthood is that teenage pregnancy and birth rates have plummeted since the 1990s. But 20-somethings are the new teens: Unwanted pregnancies soared in this cohort during that same period. Among single women under 30, about 70 percent of pregnancies are unplanned; just under half of these pregnancies are carried to term.

The resulting children are the product of unstable relationships. In one study of 5,000 newborns in large and midsize U.S. cities, half the parents were living together at the time of birth; another third were dating. But by the time the children were age 5, only one-third of those couples were still together — compared with 80 percent of their married counterparts.

More disturbing, many of those single mothers went on to have additional children with other partners, introducing new layers of instability into their children’s already complicated lives.

Certainly, single parents can be dedicated and capable caregivers. Yet the broader trend toward single parenthood is undeniably bad for the children involved. If marriage rates returned to their level in 1970, according to Sawhill’s calculations, the rate of child poverty would be about 20 percent lower.

Still, there is no reversing the inexorable trend against marriage. This acceptance reflects a shift for Sawhill, who just a couple of years ago was asserting that “Dan Quayle was right” when he criticized television character Murphy Brown for choosing unwed motherhood. Marriage, Sawhill argued then, should be celebrated as “the best environment for raising children.”

She still thinks so. “Marriage is beneficial,” Sawhill writes. “But when marriage has virtually collapsed among so many members of the youngest generation, the fact that it is still alive and well for the elites does not leave much room for optimism.”

Consequently, the more effective argument to sexually active 20-somethings is not to hurry up marriage — it’s to slow down the decision to have a child.

Which leads to the second point: There is a relatively easy and inexpensive (compared with child-bearing) technological solution at hand.

The most popular contraceptive methods have high failure rates, due more to misuse (or non-use) than to product shortcomings. Thus, 18 percent of condom users and 9 percent of those who take birth control pills will become unintentionally pregnant in the course of a year.

The smarter alternative is encouraging young women to switch to LARCs — long-acting reversible contraceptives such as IUDs, which can remain in place for as long as 12 years, or implantable birth-control, which can last for three years.

The insights of behavioral economics are at work here: To achieve the desired outcome, switch the default, from having to take active steps to prevent pregnancy to having to take action to achieve it. These methods, Sawhill writes, “are forgiving of human frailty.”

Government can’t and shouldn’t force young women to use LARCs. It can — thank you, Affordable Care Act — make them readily and affordably available. Turning drifters into planners, in Sawhill’s phrase, would not only be far better for Generation Unbound. It would give their wanted children the opportunity they deserve.

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