Asked who the record holder is on her Web site, Wendy says one donor has fathered 20 children.
So far, more than 1,600 people have found biological family members through Kramer's Web site they didn't know they had.
"And there've been many stories of people meeting," Wendy says. "First e-mailing on the Internet and then, you know, flying all over the country to meet each other and it's like — it's redefining family. It's making family where there was none."
They are new families like Justin Senk, Erin and Rebecca Baldwin, and McKenzie and Tyler Gibson. Just looking at them you wouldn't know there is anything remarkable about them, aside from a certain family resemblance, until you hear their story.
They're the sons and daughters of three different mothers, and each of them was conceived with the sperm of the same anonymous donor, No. 66 at the Rose Medical Center. The kids met after finding each other online through the Donor Sibling Registry and, incredibly, they all live in the Denver area.
Tyler thinks there is definitely a bond between the five children, beyond the fact they know they are half-siblings.
"Even the first time that we've met each other, it was just kind of like, you know that there's something more to than just knowing who they are," he explains. "There was something else there."
As soon as they met, they noticed striking similarities, more than just the same fair skin and blonde hair
"When I saw McKenzie, my jaw dropped because I was like, 'That looks exactly like I did when I was 11," Rebecca remembers.
They share half their DNA, and provide a fascinating study of nature vs. nurture. They can see aspects of their personalities reflected in each other — but that only makes them more curious about where it all came from.
"It's always been really interesting to me to know where my personality came from. And, yeah, I see it a lot more in these guys," says Rebecca. "And it's great to have half-siblings, to see that, 'Oh, that's where my personality came from, that.' But it'd be even more interesting to see it straight from the source."
They'd like to see a picture of donor 66, and know why he decided to donate the sperm that helped create them. But unless he decides to step forward, that is not likely to happen. Only a small percentage of donors have shed their anonymity, which is why Robin Anderson and Cindy Brisco were shocked when they went online and saw that their donor had posted a note saying that he was willing to be contacted.
"That night, I clicked on his e-mail. And I said, 'Are you 48QAH? And if you are, I have an incredible child to tell you about,'" Robin recalls.
Behind the mysterious 48QAH was now a face, and a name: Matthew Niedner, a 34-year-old pediatrician living in Ann Arbor, Mich. "QAH," it turns out, stood for "quite a hunk" at the clinic where he had donated sperm for seven years.