In a statement issued Thursday, Senator Mikulski said: “One of my hearings revealed that a woman was denied coverage because she had a baby with a medically mandated C-section. When she tried to get insurance coverage with another company, she was told she had to be sterilized in order to get health insurance. That will never, ever happen again because of what we did here with health care reform.”

Peggy Robertson, 41, who lives in Centennial, Colo., is the woman to whom Senator Mikulski referred. Ms. Robertson was interviewed by The New York Times in June 2008 and testified at the hearing last October. Her husband, a chiropractor, is self-employed, so they rely on the individual market to cover them and their two sons. In 2007, they had insurance, but considered switching companies when a broker suggested they might find a better deal. They applied to a company called Golden Rule, which is based in Indianapolis and owned by UnitedHealthcare. The company rejected Ms. Robertson because of her Caesarean, explaining in a letter that she would have been eligible if she had been sterilized. When Ms. Robertson went public with her story, the word “sterilized” seemed to provoke particular outrage, she said.

Golden Rule later began offering coverage to women who had had Caesareans, but by charging extra if they wanted maternity coverage, or issuing policies that excluded maternity care.

In a telephone interview on Friday, Ms. Robertson said: “Barbara Mikulski told me, she promised me, ‘This will never happen again.’ She did it. It’s wonderful.”

Ms. Robertson’s only disappointment was that some of the new rules would not take effect until 2014.

But Ms. Greenberger said that while it is true that the specific requirements will be delayed until 2014, some changes should actually happen much sooner, because the law’s overarching ban on sex discrimination takes effect immediately. The legalese outlawing sex discrimination is not easy to find or to parse, but it refers to existing laws, like the Civil Rights Act and Title IX, to say that the same protections apply to people seeking health care and insurance.