It's not "use it or lose it" when it comes to women and their health insurance; it's "use it or don't use it and still pay more than a man."

The gender gap between what women pay for health insurance and what men pay was a major issue that the Patient Protection and Affordable Care Act intended to address. And while major sections of the law do just that, a new Mercer study reveals that there's much work to be done if the gender gap in insurance premiums is to be truly eliminated.

That gap can be a monster, because it varies state by state. In 2012, the National Women's Law Center took at look at the gap as the PPACA was about to kick in. Among its findings:

• Gender rating, the practice of charging women different premiums than men, results in significantly higher rates charged to women throughout the country. In states that have not banned the practice, the vast majority, 92 percent, of best-selling plans gender rate, for example, charging 40-year-old women more than 40-year-old men for coverage. Only 3 percent of these plans cover maternity services.
• Based on an average of currently advertised premiums and the most recent data on the number of women in the individual health insurance market, the practice of gender rating costs women approximately $1 billion a year.
• There is such wide variation in differences women are charged both within and across states — even with maternity care excluded — that it is difficult to see how actuarial justifications could explain the difference. For example, one plan examined in Arkansas charges 25-year-old women 81 percent more than men for coverage while a similar plan in the same state only charges women 10 percent more for coverage than men.

That was two years ago. Mercer's data — from 2013 — provides a window into how well the PPACA addressed such inequities in its first full year. The short answer: Not very well, especially when another factor — the gender gap in pay — is factored into the equation.