In a heterosexual marriage, the mother and father are assumed to be the legal parents of achild born into the union. This is true even if the birth was the result of artificial insemination or through a surrogate mother.
In the case of homosexual unions however, this is not the case. Most states do not recognize marriages between gay and lesbian couples, meaning that the union is not a legal one in the eyes of the law. As a result, when one of the parties gives birth to a child, the “spouse” is not automatically considered to be a legal parent.
This can create problems in a number of circumstances. For example, if the child needs emergency medical care, the non-legal parent may not have the ability to authorize the treament. Picking the child from school can also become a problem as most schools will not release young children to anyone who has not been designated by the legal parent. Also see this book on Gay and Lesbian Medical Rights.
A much larger problem arises if the couple breaks up or the legal parent passes away.
In either of those scenarios, the non-legal or second parent will likely have few rights regarding the child. While there are a small number of state courts that consider the second parent to have equal rights to the child regardless of biological or legal ties, most courts look only at biological and legal rights and go no further.
As a result, many second parents can spend years living as part of the family unit, raising the child and contributing as a parent normally would only to discover during a breakup that they have no legal rights to the child at all.
To prevent this type of trauma to parent and child alike, same sex parents are encouraged to pursue legal adoption in states that allow it and draft parenting agreements where adoption is not allowed.
Adoption would establish the second parent as a legal parent, removing any question of parental rights and responsibilities. While not as binding as adoption, a parenting agreement would establish the legal parent’s intent to have the second parent continue in their duties as a co-parent and could perhaps help persuade the court to grant visitation in the event of a breakup.