SUMMIT COUNTY, Colo. -- A woman who was seven months pregnant was killed Tuesday morning when the sport utility vehicle she was riding in plunged off Interstate 70, just west of the Eisenhower Tunnel.

Her fetus was also killed, the Summit County coroner said.

Witnesses said a man driving the white Nissan Pathfinder lost control on a patch of slush or snow and the SUV went off the edge of I-70, rolling several times before coming to a rest -- 350 feet below the highway.

Crews from Lake Dillon Fire Rescue, Summit County Mountain Rescue and the Colorado State Patrol rushed to the scene and had to rappel down the steep embankment to get to the victims.

The rescue effort occurred in the middle of a spring snowstorm and took several hours. Rescuers said they were hampered by the heavy snow, poor visibility and the location of the vehicle at the base of a steep mountain bank.

After stabilizing the vehicle and rendering emergency medical care to the injured, emergency responders then lifted the victims up the steep slope by pulling them on a sled to the waiting ambulances.

One woman was thrown from the SUV, another woman was trapped but a man was able to climb out of the wreck and call for help.

The pregnant woman was identified as Analisette Sapien of Frisco, Colo. She was in her mid-20s and a resident of Summit County. She was sitting in the back seat and was partially ejected. She was not wearing a seat belt, authorities said.

The driver of the 1999 Pathfinder was identified as Jose Bucio, 28. The front-seat passenger is Zulma Fuller, 33. Both Frisco residents were wearing seat belts and sustained serious injuries. They were transported to Summit Medical Center in stable condition.

The crash occurred at about 8:11 a.m. on eastbound I-70 at mile marker 212 near the tunnel.

The crash remains under investigation.   It's not known if charges will be filed. Alcohol or drugs are not suspected as contributing factors.