A lesbian couple’s desire to adopt each other’s children has grown into a potentially groundbreaking challenge to Michigan’s ban on same-sex marriage.

Two Detroit-area nurses [Jayne Rowse and April DeBoer] filed a lawsuit to try to overturn restrictions on adoption by same-sex partners. But at the judge’s invitation, the case took an extraordinary turn and now will test the legality of a 2004 constitutional amendment that stipulates Michigan only recognizes marriages between a man and a woman.

U.S. District Judge Bernard Friedman will hear arguments in the case Thursday at a Detroit law school, although he hasn’t indicated when he’ll make a ruling. If he concludes the amendment violates the U.S. Constitution, gay-marriage supporters say same-sex couples would immediately be allowed to wed and adopt children. {…}

During a court hearing in August, the judge suddenly changed the case — and raised the stakes — when he said Rowse and DeBoer should consider challenging Michigan’s ban on gay marriage, which was approved by 58 percent of voters nearly a decade ago. So they expanded their lawsuit to claim the prohibition violates the U.S. Constitution’s Equal Protection Clause because it treats same-sex couples differently than heterosexual married couples.