The baby at the centre of a multi-state legal fight after the surrogate mother refused to terminate her pregnancy is in critical condition following complex heart surgery, the boy’s biological parents claimed.

Nasheen Gilkar and Omar Ahmed, who are battling surrogate McKenna West over custody of the boy, claimed the baby underwent the open-heart surgery  known as the Norwood Procedure, TMZ reported.

Over the last 24 hours, “Serious medical developments have arisen that impact the health and safety of the child. The child is in critical condition and being closely monitored at the hospital,” Gilkar and Ahmed said, according to court documents.

The parents claim that the baby, who they named Rumi, has seen his condition decline “significantly” after suffering potential complications from the procedure.

Gilkar and Ahmed are currently suing West, a 28-year-old nurse from Alaska, for more than $100,000 for keeping the baby rather than abort it at their request, according to the lawsuit.

They had agreed to pay West $60,000 to carry their child — with an abortion clause that allowed them to terminate the pregnancy if there were issues with the fetus, who was diagnosed with hypoplastic left heart syndrome.