This 24-year-old mistakenly thought her health insurance covered her pregnancy—and 4.2 million others like her may be at risk

Bethany* is like many first-time mothers preparing for the arrival of her baby, attending childbirth classes and setting up the nursery — "really just a large closet more than an actual room," she says — with finds from Facebook Marketplace.

"My husband will hold up the newborn size outfits and announce he doesn't believe it, nobody can be this small," the 24-year-old says, adding she and her husband always knew they wanted kids.

But while the couple planned to have a baby, they weren't expecting it to be so expensive. Despite Bethany's best intentions, only a small fraction of her pregnancy-related health-care costs are covered by her insurance company.

They learned the upsetting news at their very first doctor's appointment. "When we found out [about the pregnancy], I scheduled an OB-GYN visit to figure out next steps with prenatal care," Bethany says. It was a pretty typical visit. The office drew blood and ran tests, and her doctor spent time talking to the couple about what to expect during the pregnancy.

What Bethany didn't expect: Learning her insurance company wouldn't cover the vast majority of her medical expenses during her pregnancy. And getting a $3,000 bill for a single OB-GYN visit.

Bethany and her husband had no idea insurance was going to be an issue, since she's insured through her parents' plan. But it turns out that was the problem. Bethany says her Michigan-based insurer, ASR Health Benefits, said her mother's health insurance plan doesn't cover maternity care for adult dependents and only paid a portion, about $1,000, of that initial OB-GYN bill that it deemed "prenatal care." ASR did not respond to multiple requests by CNBC for comment and clarification of its policies.

"It feels misogynistic to me," Bethany says. A 20-year-old woman may need multiple ultrasounds during her pregnancy and end up paying thousands out-of-pocket. Meanwhile, should her 23-year-old brother need an ultrasound to treat a tendon tear, his care typically would be covered.

Bethany married her college sweetheart a year and a half ago. But because her husband has had a few different jobs since graduating, most of which were contract positions with lackluster benefits, Bethany opted to stay on her mom's insurance. Young adults can remain on their parents' insurance until they're 26, regardless of marital status.

It seemed ideal: Her parents have had some health issues in recent years, which meant they always hit their deductible. They had no idea about the dependent exemptions until it was too late, Bethany says.

In hindsight, it would be more affordable if Bethany was unmarried and therefore had a lower household income so she could claim Medicaid benefits, or if she taken out her own policy through a marketplace. While there are some federal laws that protect maternity rights, Bethany falls into a loophole.

For years, federal laws have stipulated that employers need to cover maternity care for their employees and their spouses. But there are no laws that specifically state companies have to cover maternity care for adult children because, until the ACA passed in 2009, most employer-based health insurance plans cut off coverage when the children legally became adults or upon college graduation.

The ACA changed the rules, allowing dependent children to stay on their parents' health insurance plans until the age of 26. The law also blocked insurers from turning away pregnant women and stipulated that maternity care was an "essential health benefit."

On the surface, it seems like that should have solved everything. But the ACA's essential health benefit stipulations apply only to individual health-care plans sold through the marketplaces and those offered by small employers (less than 50 employees), which is only a small percentage of plans. The bulk of Americans, 49%, get their health insurance through their employers, according to the Kaiser Family Foundation. Yet large employer plans (those with more than 50 employees) are not required to comply with the essential health benefit requirements.

Also exempt from these restrictions (unless mandated by the state law) are employers who opt to offer a self-insured (self-funded) health plan, says Julie Stich, vice president of content for the International Foundation of Employee Benefit Plans. These self-insured health plans may be run and handled by an insurance carrier, but the company is ultimately responsible for paying out on claims, instead of paying the insurer a premium.

"There are all these disparate puzzle pieces fitting together and not fitting together," Stich tells CNBC Make It. Even many student health plans provided by colleges and universities, especially if they are self-funded, do not offer comprehensive maternity coverage, according to Young Invincibles, an organization focused on policy needs for younger Americans. It's estimated that about 3 million young people are covered by these types of health-care plans, according to the Centers for Medicare and Medicaid Services.

Making it even more complicated is the fact that maternity care is not an all-or-nothing scenario in most cases. Some maternity care costs, termed "prenatal services," are routinely covered by insurers, even if the woman is an adult dependent. These covered costs generally include prenatal vitamins, as well as screenings for STDs, anemia, gestational diabetes, Rh incompatibility and preeclampsia. However, other routine tests and services are not, including chromosomal screenings, ultrasounds and copays for office visits, which can make budgeting and planning a challenge, to say the least.

Bethany is far from the only young woman facing these circumstances. "This is not an anomaly; this happening pretty consistently," says Dorianne Mason, director of health equity and reproductive rights and health at the National Women's Law Center.

Currently about 4.2 million women ages 19 to 25 have coverage as dependents on their parent's employer insurance plan, according to an analysis of 2019 Census data performed by New York University professors Ougni Chakraborty and Sherry Glied on behalf of the Commonwealth Fund for CNBC Make It.

In the U.S., the average woman has her first child at age 26, but many women get pregnant much earlier. Almost half of women with some college education have children before 25, while the median age for women with a high school diploma or less to have their first child is just 24, according to the Pew Research Center.

CNBC Make It reached out to the biggest insurance companies in the country to see if their employer-based plans included maternity care coverage for adult dependents. Cigna and Humana did not respond to queries. Beyond asking for clarification of the request, Anthem and UnitedHealthcare did not either.

Aetna and Blue Cross Blue Shield said they could not provide that information, and neither company would confirm nor deny they had employer-based plans that excluded this coverage.

The insurance industry's trade group, America's Health Insurance Plans, told Make It in a statement that "specific coverage and benefits are going to vary depending on the employer, the insurance provider, the individual and the plan they choose," and added it did not have specific data or statistics on this.

Across the country, the hospital bill for vaginal delivery costs an average of $30,570, according to estimates from the independent nonprofit organization FAIR Health. Women who undergo a C-section delivery stay in the hospital an average of three days and are typically billed $47,360. Depending on the mother's insurance plan, she'll likely pay out-of-pocket for some portion of the bill.

But the health-care expenses for Bethany and women in her situation start well before labor and delivery. Beyond that first OB-GYN appointment, women generally have another seven to 12 appointments during a normal pregnancy.

On average, the cost for doctor's visits range from about $90 to $500 per appointment, according to research site ValuePenguin. But then each additional service, such as ultrasounds, is billed separately and can range from $100 to $2,500 for special tests like amniocentesis.

When Bethany discovered that her mother's plan wasn't going to cover all of her pregnancy costs, Bethany knew she needed to find a new provider — and fast. "I jettisoned my old OB-GYN, called around and found a practice that lets me self-pay for about $500 a visit, not including some labs and stuff like ultrasounds," she says.

Since April, she's been seeing the doctor about once a month, but now that she's closer to her due date, the visits have been bumped up to twice a month, and $1,000 out-of-pocket.

Bethany has also been trying to negotiate her $3,000 bill from the initial doctor's visit, but says "they've been a brick wall about it." She finds the whole process "unfair" because the insurance company typically doesn't pays sticker price.

Additionally, she's unable to take advantage of uninsured rates sometimes offered by doctors because technically, she has insurance. "My current OB-GYN is affiliated with a hospital that has an automatic 20% discount for uninsured patients, but they told me they won't give me the discount since I have insurance, as far as they are concerned."

It can be stressful for women who find themselves in this situation because there are not many comprehensive health coverage options, says Erin Hemlin, who oversees health policy and advocacy for Young Invincibles.

For example, short-term, limited duration insurance policies may seem like a good option because you can buy one at any time of the year and these can be 20% less than the lowest-cost ACA plans, according to research last year from Kaiser. And, because of changes by the Trump administration, Americans can stay on this type of insurance for up to three years.

But Hemlin says a majority of these plans don't actually cover maternity care either. Of the 24 short-term health-care plans offered by big online providers, Kaiser found none offered maternity coverage.

Meanwhile, Medicaid and hospitals' charity care programs have income caps based on household size and state residency. Even those who do qualify for these programs may face huge bills. Under ACA, non-profit hospitals are required to provide free or discounted care to low-income patients, but about half, 45%, sent bills to patients who would otherwise qualify, Kaiser found. Some of that medical debt is later written off, but other hospitals have sent unpaid medical bills to collections, according to Kaiser.

"I know this is stereotypical, but I feel like we're kind of being punished for doing everything 'right' — we're married, financially responsible," Bethany says. "The result is not qualifying for Medicaid or assistance from the hospital."

Many times, it's up to the individual to do the research and fight for coverage. For those who are denied coverage for prenatal services, but believe they should be covered, the National Women's Law Center has a hotline and email service called Cover Her that women can call to get help.

After months of fighting with her insurance and paying $7,500 out of pocket for care, Bethany signed up for an individual Obamacare plan during open enrollment this month. The plan will go into effect January 1, 2020, so ideally Bethany's labor and delivery costs will be covered. It's going to a close call: She's due the first week of January.

"We are hoping like crazy she waits," Bethany says.

* Subject asked to be identified with a pseudonym to protect her privacy

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