When a married man and woman have a child, the husband is presumed to be the baby's father, even if he is not the biological father.
The situation is trickier when it comes to children you and your same-sex spouse planned for together but are not yours biologically. For example, this happens in situations where one woman in a lesbian couple bears a child or when two gay men enlist a female friend to carry one of their biological children. In some circumstances, both same-sex parents' names might be able to go on the birth certificate, but the rights of the nonbiological parent are not as ironclad as they would be in the case of an opposite-sex couple.
Protecting your parental rights
Not being your child's legal parent can affect your ability to make medical decisions and other important decisions, especially if you visit another state or country not as accepting of same-sex parents. In addition, if you and your spouse were to divorce, he or she could make a case that you do not deserve joint custody or even visitation. Whether such an argument would succeed depends on a lot of factors, but unfortunately, these arguments do sometimes prevail. Adoption ensures you are on the same legal footing as your spouse should you ever separate.
When it comes to estate planning and your death, your legal heirs, such as parents, siblings and perhaps biological children, may claim your nonbiological child is not entitled to any of the estate. They could show there was no legal relationship between you and the child and make a relatively simple case quite complicated. Why leave that up to chance?
With some lesbian couples, the situation can be even more complex. Reciprocal IVF lets you get pregnant with your wife's biological child. Your wife would then have to adopt her own biological child to be on the same legal footing as you.