A B.C. couple says they feel lucky to have two children, whose births would not have been possible without embryo donation.

Vancouver residents Beth McInnis and Neville Lok married in their late 30s, and both wanted children.

McInnis said she got pregnant "right away," but the excitement soon gave way to devastation.

"All of the sudden we would go in and the heartbeat had stopped," she told CTV News.

After the first incident, McInnis had numerous miscarriages before the couple decided to try In-Vitro Fertilization (IVF). During IVF, a doctor or specialist manually combines an egg and sperm in a laboratory dish, and then transfers the embryo to the woman's uterus.

But the procedure didn't work for McInnis.

"It's devastating as a woman, I think, because this is something you should be able to do," she said. "This shouldn't be a problem. There's no reason why I shouldn't be able to carry."

The couple considered adopting a child, but they were now in their 40s and found that people were choosing younger parents. They felt like time was running out.

Then McInnis learned of a little-known option that some infertile parents are turning to: adopting a frozen embryo.

There are thousands of frozen embryos left over from IVF treatments in North America, belonging to couples who successfully conceived a child.

Rather than destroying the embryos, some are choosing to freeze them in case they want to undergo another procedure, or donate them to couples who haven't been able to conceive on their own.

In Canada the process is known as embryo donation, but the majority of donations are made between couples who know each other. Some fertility clinics will coordinate donations and facilitate open adoptions with couples in the States, who are willing to sell or donate embryos to strangers.

Some clinics use 52 as the upper age limit, but they take women's health into account, and older women are able to give birth through the procedure.

"I certainly have cared for pregnancies of women in their older 50s," BC Women's Hospital Obstetrician Dena Bloomenthal said.

In the case of 45-year-old McInnis, Bloomenthal said age was a factor in why she was unable to carry a pregnancy to term. Her best chance to conceive would be to use a younger woman's egg or a younger couple's embryo.

She went to a clinic in Washington State, where an embryo donated by a younger couple was transferred to her uterus.

"Suddenly we have a viable pregnancy," she said.

Her pregnancy was closely monitored at BC Women's Hospital, and she delivered baby Tristan without complications.

"Giving birth to him was an amazing experience," her husband said.

McInnis and Lok stayed in touch with the couple who donated the embryo, in an open adoption that started soon after conception and has continued over the last two years.

Nine months ago, the adoption agency contacted the couple and asked if they wanted to try again. McInnis, now 47, recently gave birth to Tristan's sister, Danica.

"I never expected that we'd have a family of four with two kids," Lok said.

"I lay in bed and I think to myself, 'Wow, we are just so lucky and blessed.'"

With a report from CTV Vancouver's Mi-Jung Lee