An asylum seeker from Mexico suffered a miscarriage after she tripped and fell while shackled in immigration detention, even though pregnant detainees are not supposed to be restrained, her lawyers said.

Monserrat Ruiz was given a pregnancy test after arriving at an immigration detention facility in Bakersfield, California, in May, yet she was “fully shackled in leg and arm restraints” on a trip to the hospital, the American Civil Liberties Union of Southern California wrote in a letter Thursday to Immigration and Customs Enforcement.

Pregnant detainees are not supposed to be restrained barring “truly extraordinary circumstances,” for example, if a woman presents a threat to herself or is an immediate flight risk, according to ICE’s national detention standards.

The GEO Group, which runs the 400-bed facility in Bakersfield, said additional training and procedures were implemented following Ruiz’s case to ensure that policies on restraints are properly followed, “including in cases when a pregnancy may not be immediately known.” GEO declined to discuss details of the case.

Immigration officials said they are reviewing the allegations.

“While that inquiry is still ongoing, ICE’s preliminary review of documentation and witness statements associated with this case indicate many of the allegations are unsubstantiated,” the agency said in a statement.

Ruiz arrived on the U.S. border in early May seeking asylum after fleeing threats to her family. She was transferred to the Bakersfield facility. After experiencing heart and breathing complications, she was taken to the hospital May 10, where a doctor determined she was pregnant, the ACLU said.

In the following days, she suffered health problems and was shackled and taken back to the hospital, but she tripped and fell in transit. Ruiz returned to the detention facility and began suffering symptoms of miscarriage the next day, the ACLU said.

Ruiz, who is 24, was a couple of weeks pregnant, and she only learned of her pregnancy in detention, said Eleni Wolfe-Roubatis, Ruiz’s attorney. A guard from the detention facility accompanied Ruiz on the doctor’s visit when she learned of the pregnancy and was given a copy of her hospital records, she said.