McKenna West pictured in this undated handout photo from an Alliance Defending Freedom press release. Alliance Defending Freedom

A 28-year-old surrogate mother in the United States is facing a lawsuit from the biological parents of a baby she carried after she refused their request to terminate the pregnancy following the discovery of a serious heart defect.

According to a report by TMZ on Thursday, Nasheen Gilkar and Omar Ahmed filed a countersuit against McKenna West weeks before she gave birth to their baby in Texas.

Gilkar and Ahmed had agreed to pay West $60,000 to serve as a surrogate, with an abortion clause in their agreement allowing them to terminate the pregnancy if problems with the foetus were discovered, according to the lawsuit.

However, at about 20 weeks into the pregnancy, the baby was diagnosed with hypoplastic left heart syndrome, a rare and life-threatening congenital heart defect.