Elton John's Baby: Whose Sperm is It?

(CBS) Elton John and husband David Furnish had a special Christmas gift this year - a beautiful baby boy named Zachary Jackson Levon Furnish-John.

"We are overwhelmed with happiness and joy at this very special moment. Zachary is healthy and doing really well, and we are very proud and happy parents," the two dads told US Magazine.

But the joyous news left some interesting medical questions: how did the two dads do it and whose sperm is it?

So far, the couple has said only that they used a surrogate mother. The rest of the details, they say, will remain private. So CBS News asked Dr. Masood Khatamee, a fertility specialist and clinical professor at New York University, to explain the options.

"The technology of reproductive medicine has approached the state where anything is possible," he says. "For those that can afford it."

The least expensive option, says Khatamee, is to make a contract with a surrogate mother then artificially inseminate her with sperm from either John or Furnish. But the legal issues can be tricky, if the mother wants to keep the child after giving birth.

A second option, he says, is to hire two women: one to provide the egg and another to provide the womb. In this scenario, an in-vitro fertilization specialist would merge sperm and egg in a lab, then implant several pre-embryos into the second woman's womb. It's an expensive process - up to $50,000, says Khatamee - and only succeeds about 40 percent of the time in the best of circumstances. The big advantage is legal, he says. The woman who births the child has a lesser claim to it, if she wants to keep it.

There is also a third intriguing option, he says. Fertilize an egg with sperm mixed from both John and Furnish. That way either one could be the father.

It's a practice usually reserved for men with fertility issues.

"Sometimes we offer the mixing of husband and donor sperm together," says Khatamee. "This way the man feels psychologically like he is part of the process."

Khatamee says he has been helping homosexuals become parents for at least 15 years, but notes "in the past five years we have seen a big increase in gay couples using this technology."