(CBS) At the Golden Globes, lots of celebrities thanked their agents. Rocker Keith Urban and actress Nicole Kidman thanked their "gestational carrier."

"No words can adequately convey the incredible gratitude that we feel for everyone who was so supportive throughout this process, in particular our gestational carrier," the married couple said in a statement a day after they walked the red carpet at the award show.

Turns out the celebrity couple are the proud parents of their second daughter, Faith Margaret, and they had some modern help in doing it.

According to Dr. Alan Penzias, a fertility specialist at Boston IVF and an associate professor at Harvard Medical School, a gestational carrier is a woman who carries another couple's fertilized embryo to term. She would be the carrier of the child, but not its genetic mother.

"Surrogacy is the problem we had in the past, the woman who carried the baby it was also her egg," he tells CBS News. "This is a much cleaner circumstance. Typically women who are gestational carriers love being pregnant and they want to help couples carry a baby."

For lots of women, the idea that someone may love pregnancy may seem strange, but Penzias insists, "Often they have had their own children and know the joy of having a baby. They typically have a great relationship with the intended parents. They all get to know each other."

There are no medical details forthcoming from Kidman and Urban, and Penzias has not consulted on their case, but he says there are many medical reasons why a couple would use a gestational carrier: some women are born without a uterus but have healthy eggs, others have had their ovaries removed, and still others may have heart or health problems which make pregnancy dangerous.

"If the burden of pregnancy is imposed on someone with a bad heart, it could kill both mother and child," he says. "Through in vitro fertilization (IVF) and gestational carriers, that woman can be a genetic mother and have a safe experience."

The process is not without its hurdles. Parents and the carrier undergo extensive genetic screening to make sure the baby will be healthy and and psychological tests to ensure everyone can handle the unique strain of the situation.

It's also not cheap. It runs up to $15,000 for the IVF treatments and another $25,000 for the carrier, he says. But Penzias says not all of his clients are rich.

"I have seen couples of modest means who save up their money to have one child," he says. "People save up for a house or a car. Some people say they want their money for something much more important."