Elizabeth Banks' new baby: Where did he come from?

(CBS/AP) Add Elizabeth Banks to the list of infertile women who have become moms via gestational surrogacy. On Wednesday, the sexy "30 Rock" star - who has been frank about her fertility problems - and her husband welcomed their baby boy, Felix.

"The one true hurdle I've faced in my life is that I have a broken belly," Banks wrote on her blog. "After years of trying to get pregnant, exploring the range of fertility treatments, all unsuccessful, our journey led to gestational surrogacy: we make a "baby cake" and bake it in another woman's oven."

That's a cute way of explaining a process that can get pretty complicated, both medically and legally. Gestational surrogacy involves making arrangements with a woman to "carry" a baby to term for an infertile woman. The surrogate, or "carrier," is implanted with an embryo created using another woman's eggs. The intended parents are typically present at the baby's birth, and take over parenting responsibilities immediately, according to the University of Southern California Fertility website.

The embryo implanted in the surrogate can be created using the eggs of the intended mother or with donor eggs, according to USC Fertility. Similarly, sperm can come from the intended father or from a sperm donor.

It's not clear whose eggs and whose sperm were used to create the "baby cake." One thing that is clear is Banks is facing a busy agenda in the coming days and weeks.

"If you need me," she blogged on Wednesday, "I'll be changing dirty diapers and trying to get some sleep."