“When you say a self-managed abortion, people think about a coat hanger or a back-alley abortion,” said Abigail R. A. Aiken of the University of Texas at Austin, who has studied the safety of self-managed abortions and the reasons women choose them. “The reality is we’re sitting here in 2019, and it’s not like that anymore. You can go online, and you can fill out a form, and you can get this safe and effective technology delivered to your home.”

Some anti-abortion groups expressed alarm. “The industry’s migration to chemical self-abortion is deeply disturbing as it carries with it the possibility of increasing the overall abortion rate over time,” Chuck Donovan, president of the Charlotte Lozier Institute, said in a statement this week.

Experts disagree somewhat about how many such abortions are occurring in the United States. Some estimated a few thousand a year; others said tens of thousands. Because they are underground, it’s hard to measure them precisely. Those numbers compare with around 862,000 in-clinic abortions in the new yearly count published this week by the Guttmacher Institute, which collects the most detailed statistics about abortion in this country, and supports abortion rights.

“I have no doubt that it will become more common if access becomes more constrained,” said Daniel Grossman, a physician and a professor of obstetrics and gynecology at the University of California, San Francisco, who has studied self-managed abortion overseas and in the United States.

The current abortion pill regimen, approved by the Food and Drug Administration in 2000, involves two medications. The first, mifepristone, blocks pregnancy-enabling hormones. The second, misoprostol, causes uterine contractions. Between 2014 and 2017, there was a 25 percent increase in the share of in-clinic abortions by medication instead of by surgery, found the Guttmacher report. They were 39 percent of abortions in 2017.