This number doesn’t show the full picture of abortions in America. While the CDC requests data from 52 reporting areas, only 48 comply; one of those missing is California, which accounts for at least 20% of abortions in the US, notes Beverly Winikoff, a professor of Clinical Population and Family Health at Columbia’s Mailman School of Public Health.

And yet, no matter who’s counting, abortion rates have fallen. The Guttmacher Institute, which surveys healthcare facilities directly, estimates 13.5 abortions per 1,000 women of reproductive age in 2017, down from a peak of 29.3 in the early 1980s. The question is, why? The answer could help lawmakers protect the health of women, especially if Roe v. Wade is toppled.

Though some speculate greater restrictions on abortions may account for the lowered rate, that would be reflected in a higher birth rate, says Winikoff. But the birth rate in the US has held fairly steady—even declining slightly—over the past few decades.

Still, while the overall number of clinics offering abortion services in the US has risen, they are more concentrated in the northeast and western US. In some other states and regions, it has become harder to get an abortion. “State level abortion restrictions are on the rise,” says Ushma Upadhyay, an associate professor of obstetrics, gynecology, and reproductive science at the Bixby Center for Global Reproductive Health at the University of California, San Francisco. “In our research we have found 27 abortion deserts in the US, which are major cities where residents must travel over 100 miles to obtain abortion care.”

Another reason for a drop in the abortion rate may be that abortions and related procedures are happening outside the clinic, where they are more difficult to track. Since 2000, medication abortion has been available; the pills are self-administered and can be delivered by mail, so those abortions wouldn’t be part of the official tally. The Guttmacher Institute also found a slight uptick in the percent of women who seek care in non-hospital facilities for failed abortions.

Abortions also may have dropped because fewer pregnancies are happening in the first place. “Some studies show that sexual activity among the most fertile group, young people ages 18-24 are having sex less,” says Upadhyay. “Additionally, people are using contraception better.”

“We know that the Affordable Care Act has provided a lot more access to contraception,” Winikoff says—a conclusion borne out by several analyses. The 2010 law, which expanded access to healthcare for many Americans, meant that more women of reproductive age had insurance, which meant that prescription birth control and longer-lasting contraceptives like IUDs or implants were suddenly attainable. Previous analyses have found that decreases in abortion rates correlate with Democratic leadership, likely because they expand access to contraceptives.

A change in the Supreme Court, therefore, could impact the abortion rate in more ways than one. In the presidential debate, Biden pointed out that Trump’s nominee for the Supreme Court, Amy Coney Barrett, could support the reversal of the Affordable Care Act. “She’s written, before she went in the bench, which is her right, that she thinks that the Affordable Care Act is not constitutional,” said Biden.

Just based on the abortion rate, it’s impossible to know exactly what is causing its decline. “It’s all hypothetical until we do a study to figure out,” Winikoff says. Doing that research may become all the more important in the US, especially if abortion access does come under threat.

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