Without a one-size-fits-all approach to paid parental leave, we'releft with individual policies that are too complicated.

When San Francisco passed a new ordinance guaranteeing up to sixweeks of full-time paid parental leave for workers at companieswith more than 20 employees, you'd be forgiven for expecting to seea marked increase in leave-takers.

But that wasn't the case, according to a study funded by the Robert WoodJohnson Foundation, which highlights a nationwide need for simpler,more universal policies, according to its lead author Julia M.Goodman, assistant professor at Oregon Health and ScienceUniversity and Portland State University School of PublicHealth.

Related: Wall Street dads find parental leave easier to getthan to take

After the policy took effect in January 2017, only 13% morefathers made use of paid parental leave, and men claimed just 15.6%more time off compared to other counties.

Meanwhile, there was no change among mothers. That's at leastpartially because paid leave policies were already more widely usedby women than men, according to the study. But the findings alsounearthed a widespread lack of understanding about maternity leavebenefits, particularly among lower-income mothers — less than 2% ofwhom had accurate information about the new policy.

Goodman called those findings "surprising and distressing,"noting that lower-income workers were much less likely to say theyunderstood their benefits and that their employers do anything tohelp, compared to those with a higher income.

"That's potentially disturbing," Goodman said. "This is a spacewhere employers should really step in and provide more informationand more support for workers who need to take leave."

One of the key takeaways, according to Goodman, is that withouta one-size-fits-all approach to paid parental leave, we're leftwith individual policies that are too complicated.

"There's a lot of confusion all round," Goodman said. "To bemore effective we should try to advocate for more simple universalpolicies, as opposed to right now we have this patchwork ofpolicies at the city and state level, and they don't all align. Soeven if HR leaders really understood this and were motivated totalk to their employees about it, it's hard."

San Francisco's policy also doesn't cover small employers,meaning many low-income parents were left out.

But there was one source of information that both low andhigh-income employees consistently said they relied on: healthcareproviders.

"I think there's some potential to work with healthcareproviders or health systems to try to get some information out toworkers that way," Goodman said.

Studies have linked paid parental leave to productivity andretention in the workplace and improved physical and mental healthamong workers. Goodman says that mirrors findings from a similarsurvey asking employers how they feel about San Francisco's newpolicy, publishing later this month.

"It seems like even with a policy like this that's relativelyburdensome on employers because it asks employers to provide somepay, they were still supportive and said it didn't have a negativeimpact on them."

The best thing HR leaders can do, in Goodman's view, is supportpaid leave policies when they come up at the state and federallevel, and to encourage the business community to speak up.

"From the business community, to have their support is sopowerful," Goodman said. "In each of the states that have passed apaid leave policy, it's been critical to have businesses comeonboard and say, 'Yes, we think this is an important benefit.'"

Read more:

• Parental leave is booming, just not foreveryone
• More companies embracing gender-neutral parentalleave policies
• Report weighs different paid leaveplans