The fetus being carried by a woman declared brain dead is "distinctly abnormal", her family's lawyers say.
The body of Marlise Munoz, 33, has been maintained with technology against the wishes of her family for almost two months because of her pregnancy.
She collapsed at her Texas home in late November due to a possible pulmonary embolism as she got up to care for her first-born son, now 15 months old.
Munoz was declared dead based on neurological criteria, meaning her brain can no longer keep her body alive. But state law demands she be kept alive so long as she is pregnant. Her family says she is dead, and should be disconnected from life support.
"Even at this early stage, the lower extremities are deformed to the extent that the gender cannot be determined," the family lawyers said. The fetus had hydrocephalus - an abnormal accumulation of fluid in the cavities of the brain.
They pointed to "further abnormalities", including a possible heart problem, though the conditions cannot be determined accurately because Munoz's body is immobile.
"Sadly, this information is not surprising as the fetus, after being deprived of oxygen for an indeterminate length of time, is gestating within a dead and deteriorating body, as a horrified family looks on in anguish, distress and sadness," the lawyers said.