The steep drop in teen pregnancies and abortions in Colorado since 2009 is mainly due to one thing: free, low-cost access to IUDs.

Intrauterine devices — tiny, T-shaped pieces of plastic placed in the uterus — are the main reason Colorado’s teen birth rate fell 54 percent and the teen abortion rate declined 64 percent in the last eight years, state health officials said Thursday.

The astounding numbers, capturing the eight-year period since IUDs became an affordable option for low-income health clinics, were released along with a study estimating the state avoided paying nearly $70 million for labor and delivery, well-baby check-ups, food stamps and child-care assistance because of fewer births to teen moms.

“This is one of the biggest public-health home runs that I’ve seen in my 35-year public-health career,” said Dr. John Douglas, executive director of the Tri-County Health Department, which has six clinics in Douglas, Arapahoe and Adams counties. “The work that’s happened is really striking.”

Thanks to a grant from billionaire Warren Buffett’s family, Colorado spent $28 million during eight years supplying IUDs to 75 public health clinics throughout the state, several based inside high schools. From 2009 to 2016, the program provided 43,713 contraceptive implants to women, plus trained medical staff on how to insert the devices.

“Because of that, everything changed,” said Jody Camp, who oversees the state health department’s family planning program. “People started hearing about it, saying ‘Wait, I can get one of those (IUDs) that my girlfriends with insurance have?’ It caught on like wildfire in a really important way.”

Before 2009, clinics typically couldn’t afford to spend up to $350 per patient who wanted an IUD, instead offering lower-cost options including the patch, monthly contraception shots or birth-control pills, which cost a clinic as little as $1 per pack. Some clinics, including in Tri-County, had an IUD wait list.

Pills, patches and rings often aren’t reliable birth control for teens and young women, Camp said. IUDs, though, can prevent pregnancy for three, five or even 10 years, depending on the type.

“That can change the trajectory of your life,” she said.

Colorado’s “teen fertility rate,” measured in births per 1,000 by teens aged 15-19, has dropped considerably faster than the national rate, also in decline. From 2009 to 2014, the U.S. rate decreased from 37.9 to 24.2 births. In Colorado, the rate dipped from 37.5 to 19.4.

The program was a “game-changer” for Tri-County’s clinics, said Lauren Mitchell, the department’s family planning nurse coordinator. The health department partnered with a campaign called “Before Play” to advertise, and teens walked in asking for long-term, reversible contraceptives.

“If you’re looking at teens and the way teens lives are, it is a lot more difficult to take a pill every day or to remember to go in during your window to get your shot,” Mitchell said.

Colorado law allows those under 18 to give their own consent regarding birth control and sexual health services.

An analysis by University of Colorado researchers found the state program was responsible for as much as two-thirds of the decline in births to teen mothers from 2009 to 2015. The drop in pregnancies “averted” $66 million to $69.6 million that might have been spent on four state and federal welfare and health care programs for low-income mothers, the researchers found.

The eight-year grant is gone, but Colorado lawmakers increased funding for the family planning program by $2.5 million per year, up to $4.1 million. Also, Colorado health clinics have received more Medicaid funding because of the Affordable Care Act, which expanded eligibility for government insurance for low-income residents. Medicaid reimbursements to the 75 clinics have risen from $500,000 to about $5 million annually.