Once the clinic gets buy-in from a few patients, it purchases the sperm from a sperm bank, harvests eggs from the egg donor and combines them in the laboratory.
A single pairing can result in a dozen embryos, and the clinic keeps the extras frozen while it looks for patients who want them.
"We want to keep the embryos moving," Zeringue said. "The goal is not to create a bank."
The clinic usually has a supply of about 10 unclaimed embryos available, he said.
"While we do our best to match your stated preferences, our primary goal is to help you attain a successful pregnancy," the clinic informed Amy Hobgood in its standard email accompanying embryo profiles sent to patients.
The first profile Hobgood accepted fell through. Because of a problem with the egg donor, the embryos were never made.
She finally agreed to accept stored embryos that had been created with sperm from a 6-foot-5 college student and eggs from a music graduate who — like Hobgood — was 5 feet 8 with green eyes. Two other women were already pregnant from the same batch.
Hobgood, who lives outside Boston, had spent eight years trying to get pregnant. She had become so depressed that she didn't feel like living, she said, and the strain on her marriage led to divorce.
She turned to the Davis clinic after she was single, drawn by the price, the prospect of pristine embryos and the knowledge she would not have to deal with any that were left over.
In February, Hobgood, 41, gave birth to twin girls, Laura and Adrienne. She and her ex-husband are now getting back together. When she sees childless couples looking at her girls, she feels the urge to share her story.
"They don't realize the joy you can have with today's technology," she said.
Has the Davis clinic gone too far?
Dr. Robert Klitzman, a bioethicist at Columbia University, was among several experts who expressed serious reservations about the program, saying it essentially amounted to creating embryos for sale.
"It gets kind of creepy," he said. "There is a yuck factor. We need to proceed very carefully."
For some people in the field, the ethical considerations come down to informed consent.
"As long as people understand what they're getting into, I don't think there's anything wrong with it," said Dr. James Grifo, head of the New York University Fertility Center. "It costs a lot of money to do IVF."
Zeringue said donors and recipients are properly informed. Patients interviewed by The Times said they understood what they were getting into.
Frozen embryos owned by the clinic, Zeringue said, "are still treated ethically. They are no different than embryos that have a person's name assigned to them."
As for concerns that biological siblings could unwittingly meet someday and mix their genes, Zeringue said the chances are remote because patients are scattered geographically.