Hayek's partner, French businessman Francois-Henri Pinault, made the revelation in a New York court on Friday (04May12) during testimony in his ongoing child support battle with supermodel Linda Evangelista.
Evangelista conceived her son, five-year-old Augustin James, while Pinault was briefly separated from Hayek and has filed legal papers demanding $46,000 (£28,750)-a-month in support payments.
Pinault took the stand to testify as part of the case, and on Friday he revealed Evangelista agreed to postpone the legal action until after the birth of the couple's daughter, Valentina, as Hayek was under so much stress.
He told the court, "She was having a very difficult pregnancy. In fact, we were told the baby had Down syndrome until late May 2007. I asked Linda to delay the legal recognition process until after the birth of Valentina. It was a very difficult pregnancy... The situation was very, very complicated. She almost lost the baby."
Valentina was born healthy in September, 2007.
Evangelista also testified on Friday and she revealed her career has slowed down in recent years and she no longer earns as much as she used to, telling the court, "There's not a lot of demand for me... I'm active. I would like to work."