The United States’ abortion rate has fallen dramatically over the past decade, new federal data shows.

A new report from the Centers for Disease Control and Prevention shows that the national abortion rate declined 26 percent between 2006 and 2015, hitting the lowest level that the government has on record.

The abortion ratio — the proportion of abortions to live births — is also down to historic lows. In 2005, the abortion ratio was about 233 abortions for every 1,000 live births; in 2015, it was 188 abortions for 1,000 live births.

This decline in abortions is happening amid other positive trends in reproductive health. The number of teen pregnancies in the United States, for example, has decreased dramatically since the 1990s — and a lot of that seems to have to do with young adults using better contraception.

It is also part of an international trend, too: Separate research has found that — looking even further back in history — abortion rates in developed countries across Europe and North America are all declining. In the early 1990s, there were 45 abortions for every 1,000 women between ages 15 and 44. That figure has now dropped to 27 abortions per 1,000 women.

The declining abortion rates in the developed world, experts say, tell a story about better access to contraceptives. More frequent use of better birth control gives women more control over their fertility — and ultimately seems to lower abortion rates internationally.

”When contraceptives aren’t available, women use abortion, even if it isn’t legally sanctioned and even if it puts them at great physical risk,” Diana Greene Foster, an associate professor at University of California San Francisco who studies abortion and contraception, recently told me over email. “When contraceptives are more available, use of abortion declines.”

Why abortions — and unplanned pregnancies — are hitting historic lows

There can be a lot of explanations for why abortions are happening less frequently in the United States. It might have to do, for example, with increasingly restrictive laws that make abortions harder to access. Thirty-nine percent of women of reproductive age live in counties where no providers provide abortion services.

Some recent polling data shows that millennials are slightly more opposed to abortion than older generations, too.

But researchers who focus on studying America’s abortion rate tend to think the biggest driver of the decline is increased access to better contraception. Simply put, fewer women are getting pregnant when they don’t want to. Between 2008 and 2011 — just three short years — one study finds that the proportion of pregnancies that were unintended fell from 51 to 45 percent.

A lot of that has to do with more women using better contraceptives. In 2012, the Affordable Care Act began mandating that insurers cover a wide array of birth control with no co-payments or cost-sharing for patients. This meant that IUDs and implants — the most effective, reversible contraceptives — became a lot more affordable for American women.

Even before Obamacare’s birth control mandate, American women were already gravitating toward these more effective contraceptives. Their usage tripled between 2007 and 2011. And once these types of birth control became free, their usage increased even more. A 2018 study in the journal Women’s Health Issues finds a “small but statistically significant increase in insertions of long-acting reversible contraceptive devices after the ACA’s contraceptive mandate took effect.”

There is even some data suggesting that Trump’s election lead to a surge of even more women seeking this type of birth control, fearing they would lose coverage if Obamacare were repealed.

State-level experiments have also shown how powerful better access to birth control can be in reducing unplanned pregnancies and abortions. Colorado, for example, provided birth control for little or no cost to low-income women across the state. Between 2009 and 2013, it saw the state’s teen pregnancy rate decline by more than 40 percent — the sharpest drop in the country over that time period.

Access to birth control increased under the Obama administration, but the Trump White House is writing new regulations that could limit availability. As Vox’s Anna North reported last month, the new rules would make it easier for more employers to opt-out of offering birth control coverage.

Those rules are currently in a preliminary stage, with final versions expected in a coming month. And given what we know about the connection between birth control, unplanned pregnancy and abortion, how they are written could have a big effect on whether these positive trends in reproductive health continue.