They had extra embryos. So they logged on to Facebook.

Ryann Hendrickson’s embryos appeared under a microscope like tiny rings of translucent bubbles, each about the width of a human hair. These were leftovers: fertilized eggs that Hendrickson had created with her husband’s sperm through in vitro fertilization. She no longer needed them for her own family, but she didn’t want to throw them away.

So in May, Hendrickson messaged a popular IVF account on Instagram.

“We are really looking for someone to donate our embryos [to],” Hendrickson, 37, wrote, “and wanted to see if maybe someone in your following is looking.”

An entire ecosystem has taken shape in recent years around extra embryos like Hendrickson’s. There are reproductive endocrinologists who help people conceive and freeze remaining embryos, psychologists who specialize in the potentially messy fallout of donating genetic material, and lawyers who handle pre-birth contracts.

In Philly and around the country, there is also the energetic network of Facebook moderators and Instagram influencers who connect donors and intended parents, helping to mediate a fraught and increasingly common exchange. Many of the posts in popular online groups read like dating profiles, complete with wedding photos, jobs, and hobbies. The donations are effectively a form of mutual aid between strangers.

Social media has made it easier for families to avoid the rigid religious requirements of some embryo donation groups. Since the late 1990s, the world of embryo exchange has been dominated by conservative Christian organizations, as the Cut reported this summer. Such groups refer to embryo transfers as “adoptions,” part of a broader effort to define life as beginning at conception and limit abortion.

That’s what drove Emily, of South Jersey, to Facebook. Emily, who The Inquirer is referring to by her first name to protect her family’s privacy, had two children through IVF with her wife. When they decided not to have any more, they put the remaining embryos on ice. But having spent so much time and money creating them, it seemed foolish to throw them away, so Emily began researching how to donate.

She was horrified to discover that most of the organizations she found online excluded gay families from their recipient candidate lists and refused to accept donations from gay couples.

Frustrated, she posted on Facebook, explaining that she was looking to set up a direct donation. Mutual friends connected her and her wife with a gay couple, who were already on the long, winding journey of trying to have children themselves.

“I wanted to donate them to another queer couple,” Emily, 37, said. After meeting with the fertility clinic and with lawyers, she and her wife legally transferred ownership of the embryos to the couple last winter. (One of the recipient parents is an employee of The Inquirer.)

Although donated embryo transfers account for a small percentage of all embryo transfers each year, the annual number more than tripled nationwide in the last 15 years, according to a recent study in the American Journal of Obstetrics & Gynecology. That means a lot more conversations: In these days of direct-to-consumer DNA tests, psychologists and fertility doctors tell patients that anonymity, however well-intentioned, doesn’t really exist.

Unlike sperm and egg donors, embryo donors are not paid, beyond reimbursement for screening and storage. For a Philadelphia-based recipient, the process tends to range from $7,000 to $12,000, said Andrea Braverman, a Jefferson psychologist in the OB-GYN department and one of the pioneers of infertility counseling. That makes it simply the best financial choice for many families who can’t conceive on their own — far cheaper than paying for an egg donor or surrogate or adopting a child.

“Mostly what comes to me is, ‘I just have run out of options,’ ” Braverman said. “ ‘How do I build my family and how do I do it in a way that I can afford?’ ”

A number of fertility clinics in the Philadelphia area require patients to have a session with Braverman before donating or receiving embryos. A child may never result from the exchange, but they hash out expectations — whether photos will be shared, what to do if a child takes a DNA test 10 years down the line and reaches out unexpectedly.

“Every recipient is going to be scared to death that every donor is going to look at this kid, and go ‘that’s my kid,’ ” Braverman said. “Every donor is like, ‘I don’t want to pay for this kid’s tuition.’ ”

Both sides typically hire lawyers, like Rebecca Nayak, a partner with the Jerner Law Group in Germantown. Nayak helps families draw up the legal documents for embryo transfers and grapple with the knotty legal questions they may not yet have considered. What are the expectations for contact between genetically related kids raised in two separate families? What if the recipient family has leftover embryos from the initial donation and wants to re-donate them to someone else?

Hendrickson, who lives in Phoenixville, had created her own cluster of cells during one of the darkest periods of her life, right after a miscarriage and a breast cancer diagnosis, when the whole world was locked down. She paid a gestational surrogate to carry her second child, and was profoundly motivated by the idea of doing something monumental for another person.

This spring, she connected through Instagram with a woman in Maine looking for donated embryos. Hendrickson felt a kinship right away — the woman was a fellow breast cancer survivor, and they had coincidentally exchanged messages years earlier about pixie cuts after chemotherapy.

But still, she had fears about giving someone else the means of making a baby with her and her husband’s DNA.

“The thought would come into my head: What if I see a picture of the baby when it’s born and I have this overwhelming feeling of love for it?” she said. She met with her fertility doctor and with Braverman to talk it through.

At the end of last month, she and her husband legally transferred ownership of their embryos to the Maine couple. Hendrickson said she plans on telling her children, when they’re older.

“Once that baby is born, I’m not their mom,” Hendrickson said. “Biologically, yeah — but I’m not going to be their mother.”