The Republican health care bill currently making its way through Congress could have a major impact on how many people have access to health services through Medicaid –changes that would fall disproportionately on women.

Today, more than 17 million women in the U.S. aged 18 to 64 have health insurance because of Medicaid, according to data from the National Women’s Law Center. Nearly a fourth of these women gained access to health insurance for the first time as a result of Medicaid expansion under the Affordable Care Act (ACA) that passed in 2010.

Just within the first two years of expansion, nearly four million women were newly insured through Medicaid between 2013 and 2015 — women who are now at risk of losing health care coverage.

The Republican plan, known as the American Health Care Act (AHCA), could reverse these gains since the bill proposes drastic cuts to Medicaid. The safety-net program is projected to lose over $800 billion over 10 years, according to a newly released report from Congressional Budget Office (CBO).

Women, who are the primary beneficiaries of Medicaid, could be the hardest hit by these changes. In 2015 alone, nearly four million more women were using Medicaid than men according to the U.S. Census Bureau.

“Medicaid is a critical lifeline to health care services,” said Alina Salganicoff, vice president and director of women’s health policy at the Kaiser Family Foundation. “Now, nearly one in five women have Medicaid coverage and anything you do to change Medicaid will impact women in this country, especially the women who have the fewest resources to get care.”

Medicaid expansion under the ACA discarded “categorical” eligibility — where low-income individuals only qualified if they were pregnant, a parent of a dependent child, over age 65, or had a disability—in favor of criteria solely based on income. For the first time, it allowed low income women without children to gain access to health insurance.

Expansion was adopted by 31 states and the District of Columbia, and according to the National Women’s Law Center, these states saw the biggest leaps in Medicaid enrollment for women aged 18–64.

The CBO estimates that under the AHCA, Medicaid expansion would no longer be sustainable, with states curtailing their programs or choosing not to expand eligibility due to the lack of funds. By 2018 the CBO estimates…