A surrogate who refused an abortion request from the parents who hired her to have their baby has asked the US Supreme Court to intervene in the dispute over who should have custody of the baby.

McKenna West filed an emergency appeal asking the court to halt a previous ruling granting parental rights to California couple Omar Ahmed and Nausheen Gilkar.

Ahmed and Gilkar had asked West to abort the pregnancy after a scan at 20 weeks showed the foetus had a severe heart defect.

Instead, West – who has been supported by several Republican officials – travelled to Texas where nearly all abortions are illegal and gave birth to the child.

The BBC has contacted lawyers for Ahmed and Gilkar for comment.

West has since been pushing for custody over the baby, born last month with hypoplastic left heart syndrome, a defect where the left side of the heart cannot pump enough blood to the body.

The condition often requires multiple surgeries, which are not a cure. Infants with the condition can have lifelong complications, according to the US Centers for Disease Control and Prevention.

After West travelled to the state, Republican Texas Attorney General Ken Paxton intervened in the case and won an emergency court order requiring that the boy receive medical care in the state. He had surgery soon after birth.

West said she denied the couple’s requests to have the abortion after learning of treatment options and wanting to keep “this precious baby”, according to the Supreme Court filing.

West has argued that the biological parents should not have custody because she worries they would not give the boy necessary medical care because they sought to abort the child after learning of the life-threatening condition.

In a previous court hearing, Gilkar said the baby – whom they named Rumi – was “our child” and “the love of our lives”, according to the Associated Press. They said West travelled to Texas without telling them and blocked their access to medical information.

A California court previously granted parental rights to Ahmed and Gilkar, while a Texas court issued a restraining order blocking West from seeing the baby.

Last month, an attorney for the California couple said the child was in critical condition and seemed to be “suffering from potential complications”.

West argued that without intervention from the Supreme Court, she would no longer have access to information about the child’s medical condition. In the filing, lawyers for West suggested that the California couple could place the child in hospice care.