When the news broke late last April that Sarah Jessica Parker and Matthew Broderick were expecting twins with the help of a surrogate mom, a renewed interest in this family-building practice burgeoned. It suddenly seemed a more viable option for women unable to conceive or carry a pregnancy to term—situations familiar to many women in the workforce who have delayed childbearing until their careers were well established. But beyond coming to terms with surrogacy’s emotional price (as well as the social discomfort that still surrounds it), you need to understand its legal aspects—which are surprisingly varied from state to state.

Entering into surrogacy, which means making a contract with a woman who agrees to become pregnant and deliver a child for you, is not a choice you can make on a whim, says Mindy Berkson, a consultant at Lotus Blossom Consulting in Chicago, which helps guide people struggling with infertility. “The option is explored when medical indications prevent a woman from carrying a pregnancy to term,” she says. Women who’ve had multiple miscarriages, are experiencing secondary infertility, have a damaged uterus or none at all or have other conditions that prevent giving birth may be candidates for surrogacy. Alternative families, such as lesbian couples, may also choose this route so that one partner can be the egg donor and the other can carry the baby.

There are two types of surrogacy, and the distinction is legally important: In gestational surrogacy, the surrogate is not biologically related to the fetus she’s carrying. The embryo is created with the intended mother’s egg or a donor egg plus the intended father’s sperm or donor sperm and then implanted. In traditional surrogacy, the surrogate is the egg donor and is inseminated with either the intended father’s sperm or donor sperm. Many state laws make it difficult to use implantation, says Berkson, so for many women gestational surrogacy may not be an option.