In a busy airport, a 21-year-old girl is looking out for a stranger. She’s flown across the US to see him, after spending months exchanging messages.

It’s the first time she and her biological father will meet, but they’re about to spend eight days together. Less than a year ago he had nothing more than a suspicion that she existed.

She does a nervous dance on the spot, laughing as her boyfriend records her. Seconds later she sees who she’s waiting for, recognizing him from the photos they’ve exchanged. Her laughter turns into silent sobs before she breaks into a run through the crowd. She and her father slam into each other's arms in a drawn-out hug.

They haven’t really spoken since.

They are processing the experience, she explains, adding that she views him more as a friend. “He is my father,” says Amy*, who isn't using her last name to protect her family's anonymity like several sources in this story. “But I don’t think of him as a dad.”

Amy is one of an unknown number of donor-conceived adults worldwide—although somewhat unreliable estimates say there are 30,000 to 60,000 donor-conceived births each year in the US alone, either via artificial insemination or in vitro fertilization (IVF).

Unlike many donor-conceived people who find out later in life—sometimes during fights, or on deathbeds—Amy always knew she had a donor, although she wasn’t able to request information about him until she was 18.

Yet, she is one of the lucky ones. Many sperm or egg donors refuse to allow contact, and are well within their legal rights to do so. Across the world, efforts at reaching out to donors by their children are often met with walls of silence, threats of legal action, and even restraining orders.

Dan* discovered he was donor-conceived after he took an at-home DNA test for fun at age 28. He tracked down his donor almost four years later, and eventually sent him an email—written with three half-siblings he’d found along the way.

They never received a reply.

“He’s burying his head in the sand and hoping it goes away,” Dan speculates about his donor. “At the very least, the responsible thing to do would be respond with his health information.”

Despite the biological revelations, Dan says he still views the man who raised him as his dad, although the news has not come without its difficulties. “I think it is a concept that is incredibly difficult to understand if you’re not in this situation,” he tells me.

“For those of us who found out through DNA testing, and sort of had the rug pulled out from under us, it’s a very jarring, strange experience of ‘Oh, your family’s not your family, your ancestry’s not your ancestry.’ And it’s sort of like adoption, but it’s not.”

Perhaps one of the major differences between adoption and donor conception is that it’s easier for parents of the latter to hide their children’s status. Excluding the children of same-sex couples and perhaps single parents, there are few hints to suggest that a donor-conceived person is not the biological child of the parents raising them. When a child resembles at least one parent, or a woman goes through nine months of pregnancy, there is little reason to suspect something is amiss. In many cases, their wider family may not even be aware.

Alternatively, some donor-conceived people instinctively know something is not right. When Erin Jackson was 35, her mother told her she was conceived with donor sperm. Unlike many people, who report feeling a loss of identity after finding out the truth, Erin felt validation.

“The first thing out of my mouth was ‘I knew it!,’” she laughs. “I was filled with this sense of ‘Oh, my intuition was right! I’m not crazy, there is something different about me.’”

Erin quickly tracked down a half-sibling, and the discovery of her biological father soon followed. But over the course of two years, he ignored any attempt at contact.

Eventually, Erin made a plea for her sanity. “Until I got confirmation from him [that he was my biological father] it was really difficult to not think about that all the time. It felt so wrong that I should have to live with that question mark and uncertainty for the rest of my life,” she explains.

“I sent him a third letter just saying, ‘Hey, I need to know. For my own mental health, I need to know.’”

A month later she received a reply: confirmation that he was her donor, but little else. He refused to share medical history.

“He addressed the letter to Ms. Jackson,” Erin recalls. “It was very cold…He also requested that I not contact his family, and that made me feel around two inches tall.”

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For 32 years, Jaclyn Baxter thought she was an only child. Now, she has 11 half-siblings—and they’re just the ones she knows about.

Her decision to do a DNA test was motivated by nothing more than a general curiosity. The results arrived innocuously on Mother’s Day—a jumble of data which revealed she wasn’t the daughter of the dad who passed away in her arms 14 years earlier.

“I’ve processed it, and I’m okay with not being my father’s biological child,” she tells me. “But in the beginning I wasn’t. In the beginning my body felt invaded. And I didn’t know who made up the other half of me.”

“My dad was the greatest man,” she continues, close to tears. “And so it was hard, it not being him. It never changed my love and my feelings for my dad. It just made it a little more complicated.”

Since she got her results last year, a new half-sibling match has rolled in almost every month. “It was an enormous amount for me to process.” she recalls. “And it’s trippy to sit in front of a sibling for the first time at age 33 or 34.”

Despite the emotional turbulence, Jaclyn says her experience has been mostly positive. She’s formed close relationships with many of her siblings, become an aunt to their children, and is soon to become godmother to one of her new nieces. But she says that closeness also triggered “a new stage of grief.”

“It just makes me sad that I’ve missed out on a lot. And I’ve missed out on my brothers’ children, their births, their weddings. That part’s hard.”

Perhaps most astounding is the fact that, according to his family, Jaclyn’s biological father donated sperm upwards of 300 times, all within in a small area in the US.

“There’s potential of these kids growing up around one another, and being at the same school, or dating,” Jaclyn points out. “And that’s really fucking overwhelming...What was he thinking?!”

When Grace** was born, her mother was almost 50, and was often mistaken for her grandmother.

Then, a few days before Grace turned 20, she got the results of a DNA test she’d done for a school project. She tells me she immediately knew something was wrong.

She called her dad, who told her she was conceived using an egg donor and separate surrogate. She remembers the conversation as “a moment of shared grief.”

The anger came when she called him back, two days later.

“I asked him when he had planned to tell me, and it seemed like there hadn’t been a plan, or the plan was just to go to the grave with it. That made me really angry,” Grace says. “And that anger and frustration built as I was trying to find the donor, because the system is set up to make that very, very hard.”

After months of searching Grace found her egg donor, but the woman denied everything when contacted. “She was very curt, and kind of had a sense of ‘Leave me alone. Leave my family alone,’” Grace says. “She seemed really scared of me to be honest. And I already had a mum who lied to me. I didn’t want another.”

But the cycle of secrecy is a hard one to break. Grace hasn’t told her mother that she knows the truth. Grace’s sister is also donor conceived. She doesn’t know yet, and Grace doesn’t know if she will ever tell her.

In many ways, secrecy becomes a defining trait of donor-conceived people’s experiences. When Becky* found out the truth at age 32 after taking an at-home DNA test, she says her parents acted “like their biggest secret was discovered.” They warned her never to tell anyone.

But in a cruel irony, Becky’s parents weren’t the only ones hiding the truth. Thirty-three years earlier, they’d been assured by medical professionals that they would get a Jewish sperm donor.

“My family that raised me is Jewish, so that was important to them,” Becky explains. But her DNA test revealed that she in fact has no Jewish ancestry on her biological father’s side.

Becky has since met him—a man she says is just like her. “He knows more about me from one conversation than my dad who raised me does,” she says. “It’s like if the one thing I wanted more in the world could come true, but I hadn’t even realised it was something I could want.”

Senior portraits of Becky and her biological father.

Honesty is important, says Susan Golombok, director of Centre for Family Research at the University of Cambridge. She says that from her research, the best parent-child relationships are observed when parents talk to donor-conceived children about their situation truthfully, in an age-appropriate way.

“The people we’ve come across who have more problems are the ones whose parents haven’t told them and they’ve found out later in life,” Golombok explains. “Many of these people are more likely to say they were shocked, angry, felt deceived, upset, and distressed when they found out.”

For some, the distress is life-changing.

Matt Johnson found out he was donor-conceived in his mid-30s—a discovery which not only revealed he wasn’t his dad’s biological son, but also not full siblings with his brother. This revelation and its emotional fallout triggered anxiety, an ER visit, and cost him his faith, he says.

“Losing half of my identity caused a lot of reflection of myself—sort of looking at your own life as a stranger would. Why do you do the things you do or believe the things you've always believed? Religion is one of the things that didn't pass the test.”

But for a while, it seemed like Matt could turn the news around. He tracked down a half-sister, initially speaking openly to her on the phone for more than an hour. They exchanged emails. Then nothing.

He says that despite not really knowing his new sibling, he felt her rejection deeply. “The only brother I had growing up has been dead for a little less than four years. And [the rejection] was almost like losing him again.”

Matt says he will send his half-sister a photo when his daughter is born, in the hope that he might hear from her.

“The worst part about it is the silence,” he says. “She’s just gone, and it makes no sense.”

In the past two decades, legislation in a number of countries has changed practices around sperm donation—either to make donors identifiable or to cap the number of families they can donate to. But even then, there is no legal obligation for parents to inform their children of their biological roots.

The United States, for its part, has not taken such steps. There is no legal cap on the number of donations that can be made by a single donor—though the American Society for Reproductive Medicine does have suggested limits—and no laws to ensure children can track their biological parents. Erin calls it ‘the Wild West.’

“These sperm banks are not taking the emotional or physical health of the people they produce into account when they’re making their business decisions,” she says. “It’s totally nonsensical to have no limit on how many offspring a single donor can produce. If you have 200 siblings how are you even supposed to approach that?”

She also points to the majority of donor-conceived people opposing anonymous donations. “That should be a red flag to anybody, because we’re the people who have lived it and experienced it.” Now—decades after the mass-commercialization of donor conception began—the products of that world are finally adding their voices to the conversation.

“All people want to know where they come from,” Erin says. “This should not be shocking to anybody.”

*Last name has been omitted to protect anonymity.

**Name has been changed to protect anonymity.