Actress Sophie Nyweide Was Pregnant When She Died

Sophie Nyweide's death has another tragic element to it ... because it turns out she was pregnant at the time of her death.

According to the death certificate, obtained by TMZ, Nyweide was with child when she was pronounced dead just before 5 AM on April 14 in Bennington, Vermont.

An autopsy has been performed on Sophie's body ... but, as of now, an exact cause of death is still unknown. But, police are investigating the death as a possible unintentional overdose.

As we told you ... we spoke with Sophie's mom, Shelly, yesterday -- and she told us she knew her daughter was using drugs, saying she was a very small woman. She added Sophie was with other people when she died, but Shelly did not know them.

Police have not ruled out foul play in Sophie's death -- cops said she was found on a riverbank, and was pronounced dead at the scene. We're told a man was with Sophie when she died, and he is cooperating with cops ... though police added he's not considered a suspect or person of interest.

Shelly says the family's in mourning ... adding Sophie enjoyed acting -- and was never subjected to anything hurtful on sets like other child actors have been. Sophie appeared in several films as a kid ... including "Noah," "Bella," Shadows & Lies," and the TV show "Law & Order."

Her father remembers her as a girl who was "creative, athletic and wise beyond her years," who demanded to be an actor.

Sophie was 24.