As at home DNA tests become more common, people must grapple with surprises about their parents

• Andrea Ramirez got a DNA test for fun and learned something that changed her life.
• Her father, the man who raised her, was not her biological parent.
• Ramirez is one of thousands of people who are getting DNA tests, like AncestryDNA and 23andMe, and finding family secrets they didn't expect.

Until recently, Andrea Ramirez, 43, thought she was part Mexican.

But the results from an at-home genetic test from 23andMe revealed that she is a mix of Northern European, North African and a little Native American.

And not at all hispanic.

Ramirez, who hails from the Bay Area and works in marketing, bought the $199 genetic test in 2013 for a lark after her brother Danny's own test came back with some curious results. She and Danny are both fair-skinned and freckled, and don't closely resemble their half-siblings from their father's first marriage, but they never questioned their heritage.

As expected, Danny showed up on a list of Andrea's DNA relatives on 23andMe. But his DNA was only about a 25 percent match with hers, meaning that he wasn't a full sibling as she had expected.

More strangely, a mysterious woman also appeared on that list as a potential relative. This woman's profile stated that she was donor-conceived.

And that's when it clicked for Ramirez. Her dad, the man who raised her, was not her biological father.

'A true ethical dilemma'

Andrea Ramirez

More people than ever before are expected to buy a DNA-test this Christmas from sites like AncestryDNA or 23andMe, as well as on Amazon.com. Millions have already gotten tested. And for many of these people, the results are unexpected, shocking, and occasionally even life-changing.

The direct-to-consumer genetic testing market, which includes both health and genealogy tests, is expected to grow from about $70 million in 2015 to $340 million by 2022, according to a report from Credence Research.

CNBC spoke to a dozen people who took a DNA test to find out fun facts about their ethnic roots, then were surprised to learned they were donor-conceived. That means the men who had raised them were not their biological fathers -- instead, their parents had faced fertility problems, and their mothers had used sperm from donors at a fertility clinic.

Research from 2005 found that so-called paternity discrepancy, when a person is identified as being biologically fathered by someone other than the person they believe is the father, occurs between 0.8% to 30% in the population.

All but one of the people who talked to CNBC asked to remain anonymous out of respect to other family members.

Most of them don't regret learning the truth, but needed to have some tough conversations with their parents and were left with many unanswered questions. In some cases, they did find likely family members but that didn't always lead to a reunion.

Some bio-ethicists say that 23andMe, Ancestry and the rest should do more to educate their users about the risks and potential outcomes. Making matters more complex is that a donor who wants to stay anonymous might decline to send in their DNA, but can still be traced through their family members.

To its credit, 23andMe does warn its users in its terms of service that the information "has the potential to alter your life and worldview." AncestryDNA's website doesn't make that quite as clear, although it does stress that users might find unknown relatives.

Others believe that fertility clinics should take additional steps to alert donors that anonymity is a thing of the past. Donors should know that if any of their family members get a genetic test, they could be found.

Ramirez and many of the others who learned they were donor-conceived via a DNA test said they hope that the testing companies won't react to these stories by making it more challenging to identify and contact family members.

"It's a true ethical dilemma," said Ezekiel Emanuel, chair of the Department of Medical Ethics and Health Policy at the University of Pennsylvania. As Emanuel explains, those that are looking for their donors have very legitimate reasons to want a relationship. But donors also have a right to privacy.

"I honestly don't think we can satisfy everyone for all these cases," he said.

Andrea Ramirez

Andrea Ramirez with her mother and half-brother

What happened next

With the rise of genetic-testing, new online groups and forums like the Donor Sibling Registry are popping up to help people like Ramirez find their family members.

Ramirez reached out to the Lisa, the woman who appeared to be a family member, via Facebook. It turned out she was not related at all to Ramirez. But Lisa's mom had another daughter, Jennifer Rose Jones.

She was the one who'd taken the 23andMe test, and she turned out to be the missing link.

"We realized that her mom and my mom went to the same fertility doctor," said Ramirez. Andrea Ramirez and Jennifer Rose-Jones had the same biological father.

The parents who raised Ramirez both died several years ago, and they never hinted that she might be donor-conceived.

"Back then, it was considered good form that you never tell the children, as it's best they not know about their origins," she said.

Jones' own mother kept a letter in her purse for decades with full details about her origins. The idea is that her daughters would find it if anything happened and she couldn't tell them herself.

In this case, subsequent DNA testing backed up that these two women are, in fact, related.

Andrea has never heard back from one relative she reached out to, a suspected half-brother, and she doesn't know if he received her message or simply did not want to meet.

Ramirez and Jones are still looking for their biological father.

Despite stories like these, geneticists warn that people who get a DNA test this Christmas shouldn't jump to conclusions if they get a suspicious result. Families can obscure or hide their heritage, or they might remain ignorant of it.

Also, not all of the DNA tests on the market can be trusted to get everything right.

"There is a lot of variety in the quality with which they make the statements that they make," said Robert Green, a physician and researcher at the Division of Genetics and Department of Medicine at Brigham and Women's Hospital and Harvard Medical School. "And some of them are more rigorous than others."