Nancy D. Polikoff, an expert on same-sex parenting law and a professor at the American University Washington College of Law, said Ms. Gunn’s loss was a reflection of the unusual facts in this case and should not be considered a setback for the rights of lesbian, gay, bisexual and transgender people.

“The Brooke case gave this woman this opportunity to sue, and she just failed to meet the standard,” she said. “I think the law did its job in that regard.”