Updated

More than half of privately insured women are getting free birth control under President Obama's health law, a major coverage shift that's likely to advance.

This week the Supreme Court allowed some employers with religious scruples to opt out, but most companies appear to be going in the opposite direction.

Recent data from the IMS Institute document a sharp change during 2013. The share of privately insured women who got their birth control pills without a copayment jumped to 56 percent, from 14 percent in 2012. The law's requirement that most health plans cover birth control as prevention, at no additional cost to women, took full effect in 2013.

The average annual saving for women was $269. "It's a big number," said institute director Michael Kleinrock. The institute is the research arm of IMS Health, a Connecticut-based technology company that uses pharmacy records to track prescription drug sales.

The core of Obama's law — taxpayer-subsidized coverage for the uninsured — benefits a relatively small share of Americans. But free preventive care— from flu shots to colonoscopies —is a dividend of sorts for the majority with employer coverage.

Expanded preventive coverage hasn't gotten as much attention as another bonus for the already insured: the provision that allows young adults to remain on their parents' policy until they turn 26. That may start to change with all the discussion of birth control.

Business groups and employee benefits consultants say they see little chance that employers will roll back contraceptive coverage as a result of the Supreme Court ruling. The court carved out a space for "closely held" companies whose owners object on religious grounds. Most companies don't fit that niche.

"I don't think you will see a broad impact," said Neil Trautwein, the top employee benefits expert for the National Retail Federation. "It's a commonly offered benefit for many employers, including retailers."

The court decision involved "a very unique set of facts," Trautwein added. "Intense religious beliefs, closely held companies and the vehement objection to contraceptive coverage."

Before the Supreme Court ruling, some "grandfathered" plans unchanged since the health care law passed were already exempt from covering prevention at no cost, but that number is expected to shrink over time as employers make coverage changes.

IMS says it is still too early to discern the health care law's ultimate impact on birth control.

At least for now, it doesn't seem like more women are going on birth control because it's free. The number of prescriptions for oral contraceptives that were filled grew in 2013, but at about the same rate as in recent years.

There's also not much evidence of a shift to costlier long-acting contraceptives, such as hormonal implants. More reliable than the pill, they are gaining popularity in other economically advanced countries.

"Awareness of the provisions of the law has not been very clear sometimes," said Kleinrock. "Certainly this is something we are going to be watching."

Birth control use is virtually universal in the United States, but about half of all pregnancies are still unplanned. Forgetting to take the pill is a major reason.

As recently as the 1990s, many health insurance plans didn't even cover birth control. Protests, court cases and new state laws changed that. Obama's law is taking it another step.

Many medical groups see a strong rationale for free birth control. Contraception can help make a woman's next pregnancy healthier by spacing births far enough apart, generally 18 months to two years. Closely spaced births carry a risk of such problems as prematurity, low birth weight, even autism. And even modest copays for medical care can discourage its use.

"It's one of the most concrete ways that women have seen that the Affordable Care Act is helping them," said Amy Allina, deputy director of the National Women's Health Network, an advocacy that supports the law's requirement.