Teen births cost Maine taxpayers at least $18 million in 2010, according to new data released Tuesday just hours after Gov. Paul LePage vetoed a bill aimed at reducing unintended pregnancies among low-income women.

Between 1991 and 2010, 25,713 teen births occurred in Maine, costing state taxpayers $600 million over those two decades, according to an updated analysis by The National Campaign to Prevent Teen and Unplanned Pregnancy.

The costs would have been much higher had Maine not recorded a substantial decline in its teen birth rate. The rate has dropped 51 percent over the last two decades, saving Maine taxpayers an estimated $36 million in 2010 alone, the campaign said in a press release.

Nationally, the teen birth rate has hit a historic low. About 305,400 teen girls ages 15 to 19 gave birth in 2012, a 52 percent drop from a peak year in 1991.

Most of the public-sector expenses associated with teen childbearing involve health care, through Medicaid and CHIP programs, increased participation in child welfare, and, once those babies grow up, higher rates of incarceration and lost tax revenue due to lower earnings and spending, according to the campaign.

Nationally, teen childbearing cost taxpayers $9.4 billion in 2010, the campaign found in the new data, an update of research conducted in 2004 by Saul Hoffman of the University of Delaware.

The analysis, funded in part by the U.S. Centers for Disease Control and Prevention, estimates public costs associated with teen births compared to mothers who bear children in their early 20s.

Maine’s success in lowering its teen birth rate grew out of broad access to comprehensive reproductive health services and the teaching of age-appropriate sex education in schools, said Nicole Clegg, director of public affairs for Planned Parenthood of Northern New England.

But family planning funds have been cut over the last three years, and on Monday the governor vetoed bipartisan legislation to provide publicly funded preventive health care to low-income adults, including birth control and sexual health information, she said.

The Maine Women’s Health Initiative, sponsored by Rep. Jane Pringle, D-Windham, would have benefited 13,700 low-income women through a limited expansion of the Medicaid program, Planned Parenthood said in a Monday evening news release. The bill also included access to cancer screenings, well-woman exams, and testing and treatment for STDs. For every $1 the state spent, the federal government would have kicked in $9.

Other states with similar programs have seen significant drops in unintended pregnancies and related costs, according to research by the Guttmacher Institute, Planned Parenthood noted. Over the last 15 years, more than 20 states received federal approval for such programs, with more exploring the option under a provision of the 2010 federal health reform law that simplifies the process.

Planned Parenthood vowed to fight LePage’s veto, scheduled for an override vote in the Legislature on Thursday.

“On Thursday, Planned Parenthood supporters across the state will be counting on their elected officials to stand up to Gov. Paul LePage and push back against his extreme agenda to undermine women’s health,” Clegg said in the news release.

In his veto message, LePage said many of the individuals who would gain access to coverage under the bill — those earning up to two times the federal poverty level — could buy subsidized health insurance through the federal marketplace set up under the Affordable Care Act. Those plans cover family planning, including contraceptives, yearly gynecological exams, Pap tests, and “even voluntary sterilization,” the message states.

“For those individuals who intend to make less than 100 percent of federal poverty level and therefore do not qualify for subsidized private insurance, family planning and health clinics across the state often already charge on a sliding scale, which they indicate is affordable for their clients,” LePage said in his veto letter.