"For many years we have talked about fulfilling one of our greatest wishes by becoming parents," John told US Weekly. "And now this wish has been granted to us, we feel so blessed and lucky."
The couple, which has been together 17 years, originally tried to adopt a 14-month-old HIV-positive boy named Lev from an orphanage in Ukraine. The country rejected their application, reportedly because of John's age and because Ukraine did not recognize their gay partnership.
Though the couple has not divulged details about how Zachary was conceived, reports have said that the surrogate was implanted with a donor egg from another woman. It's not be revealed which man -- if either -- is the biological father.
California law looks favorably upon surrogacy. Intended parents don't have to be genetically connected to the baby to be recognized as legal parents, Zager said.
"He [John] went to a surrogate-friendly state and an agency that has done this for years and years, to his credit," Zager said.
Since 1989 when they worked with their first gay couple, the center has been committed to helping same-sex couples.
"We are strong believers that they have as much right to be parents as anyone else," Bubrick said, adding, "Our work with gay couples has increased profoundly in the past 10 years as more are realizing this is a wonderful option for them."
In 1992, Hall, the "Days of Our Lives" star, was one of the first celebrities to go public about using a surrogate. She appeared in People magazine and produced and starred in a television movie based on her 20-year battle with infertility that finally ended with two successful births via a surrogate.
Most, though not all, surrogacies go smoothly, Zager said. But some celebrities have found there's a dark and worrisome side to going public about surrogates.
"The most unsavory things have been done," Parker told "Access Hollywood." "She's had her phone hacked, her personal computer information hacked, she's had threats against her and true harassment. ... She's had friends threatened and family threatened and she's had family of friends threatened.
"It keeps me up every night," added Parker, who lives in New York City. "It's really incredibly upsetting to think of her so far away and me not being able to do something, beyond what I'm legally allowed to do."