DETROIT – The Michigan Supreme Court broke new ground Monday in a dispute over parental rights, saying a woman can seek custody of her partner’s child who was born before their same-sex relationship ended.

Carrie Pueblo has no biological ties to a boy who was born to Rachel Haas in 2008 but helped raise him. Pueblo insists they would have married at that time if same-sex marriage had been legal in Michigan, a status that could have given her a formal role in the child’s life even if the marriage had ended.

Same-sex marriage was declared legal in the US. in 2015, after Pueblo and Haas parted ways.

«While the decision in this case likely affects few, it is important for what it represents,» Judge Megan Cavanagh said in a 5-2 opinion.

“Justice does not depend on family composition; all who apply for recognition of their parental rights are entitled to equal treatment under the law,” Cavanagh wrote.

Pueblo and Haas had raised the child together after their relationship ended. But in 2017, Pueblo said Haas demanded that he stop having contact with the girl.

Pueblo can now go back to a Kalamazoo County court and try to prove that she and Haas would have married, if possible, when the child was born via in vitro fertilization.

If a judge agrees, Pueblo can be assessed for «custody and parenting time,» the Supreme Court said.

Haas’s lawyer had urged the Supreme Court in April to stay out of it and let the Legislature change the law if lawmakers think it would be appropriate. Judge Brian Zahra agreed with that position in his dissent.

“I am uncomfortable with the retroactive recognition of a relationship equivalent to marriage. … Courts will be required to dive into all the public and private aspects of a now-defunct relationship to make hypotheses as to whether the couple would have chosen to marry,” said Zahra, who was joined by Judge David Viviano.