Missouri women seeking an abortion regularly head to the Hope Clinic in Granite City, Illinois, 15 minutes from downtown St. Louis. More than half of the clinic’s patients come from Missouri, many looking to bypass their home state’s mandatory three-day waiting period — one of the longest in the country.

That waiting period law became more stringent one month ago, when a deceptively subtle tweak took effect to little notice. It requires that the doctor who will perform a woman’s abortion must also walk her through the state-mandated counseling session three days earlier, rather than giving that task to a qualified nurse, physicians assistant or counselor.

Reproductive rights experts in Missouri and around the country warn that it will take months before they can measure the true impact of this change, but staff at the bustling Hope Clinic are already feeling its effect.

Dr. Erin King, an OB-GYN and the interim clinic director, suggested that more Missouri women might be crossing over to Illinois to escape the onerous requirement.

“I would say in our office today we’re probably seeing double the number of patients we would see on a similar day three weeks ago,” said King, who spoke to HuffPost two weeks after the law took effect. “On the phone, every day since that law went into effect ... we have had at least five and 10 patients calling and being upset about it. Or being confused about it. Or wondering what the change was and what is happening.”

Republican state legislators who passed the bill including the waiting period measure in a special session over the summer contend it will help protect the health and safety of women in the state.

For years, Missouri has had only one abortion provider, a Planned Parenthood clinic in St. Louis, although several more Planned Parenthood outposts around the state have begun or will soon begin to offer abortion services. The reproductive health care organization, together with the American Civil Liberties Union, sought to block the law, arguing that it places an “undue burden” on women seeking an abortion, potentially forcing them to drive hundreds of extra miles and delaying their care.

But the law went into effect on Oct. 24 after a judge ruled against Planned Parenthood and the ACLU ― a result that rattled reproductive rights advocates.

“We certainly did not think this was going to be the outcome,” Alison Dreith, executive director of NARAL Pro-Choice Missouri, told HuffPost. “It kind of left the state scrambling to figure out what this means.”

Dreith said she understands firsthand how Missouri’s restrictions can drive women out of state. She opted to travel to Illinois when she had an abortion last year.

Broader research looking at state-mandated waiting periods finds they do not necessarily change women’s minds about getting an abortion. Most women have made their decision by the time they seek care, and most find a way to follow through on it.

“What they do is create hardships for women,” said Dr. Sarah Roberts, an associate professor with Advancing New Standards in Reproductive Health, a research group at the University of California, San Francisco.

Roberts worked on a 2016 study looking at Utah’s 72-hour waiting period, which it found increased women’s financial burden and logistical challenges, and pushed at least one patient past her provider’s gestational limit for abortion. Women ended up waiting an average of eight days between their initial visit and the procedure, Roberts said. She warned about an overall “lengthening and strengthening” of waiting period laws across the country.

In Missouri, the “strengthened” waiting period law will make schedules trickier for busy doctors and resource-strapped clinics. “There aren’t that many highly trained gynecologists who can do abortion procedures, and you’re now taking their time to do all of these consents ahead of time,” King said.

She also noted how unusual it is to mandate that the doctor performing a procedure handle the prior counseling of the patient. “In no other field of medicine is that the case,” King said. “Patients undergo procedures all the time where they are ‘consented’ in a very thorough manner by a trained health care professional who may not necessarily be the exact person doing their procedure.”

Eyes from both sides of the abortion debate see Missouri as a test case for how much leeway states have to introduce new waiting periods and bolster those already on the books. In 2011, not a single state had an abortion waiting period longer than 24 hours, according to Elizabeth Nash, senior state issues manager with the Guttmacher Institute, and only seven states had policies that required women to make two trips to a clinic. Now, eight states have waiting periods of 48 or 72 hours, and seven additional states require at least two visits.

“I think of this as sort of an underground trend,” Nash told HuffPost. “I don’t know if those two words can really go together, but yes, we’ve been seeing more waiting periods. And it hasn’t gotten the kind of attention that some of the other trends have.”

Meanwhile, in her clinic just outside Missouri, King is also waiting to see the full effects of this latest abortion regulation. History leads her to believe she’ll see even more patients fleeing Missouri’s restrictions and walking through her doors. Before Missouri first instituted a 72-hour waiting period, only 40 percent of the clinic’s patients came from that state, she said. By last year, the figure was up to more than 50 percent.

“The thing that is most concerning about [what is happening] in Missouri is that there are what would seem like small changes to the existing law,” Kin said, “but that will make an enormous impact on the patients.”