Former President Donald J. Trump said on the campaign trail Thursday that he wants to make in vitro fertilization treatment free for all Americans.

“Under the Trump administration your government will pay or your insurance company will be mandated to pay for all costs associated with I.V.F. treatment,” Mr. Trump said on Thursday at a rally in Potterville, Mich.

I.V.F. often costs tens of thousands of dollars. Policies to cover those costs would be difficult to implement, experts said.

Requiring insurers to pay would most likely mean passing laws in Congress or persuading a panel of experts to add I.V.F. to a list of free preventive women’s health services established by the Affordable Care Act, the health coverage law Mr. Trump tried to repeal.

Having the government pay directly for I.V.F. would mean creating essentially a single-payer health care system for a single condition. The approach would require Congress to fund a new division of a federal government to oversee the program.

“The president cannot do this on his own,” said Alina Salganicoff, director of the women’s health policy program at KFF, a health research nonprofit. “You need to have federal funds to do this. Congress needs to appropriate money.”