Five people, including two children and a pregnant woman, were killed early Saturday in Maryland after truck crashed and rolled over on top of a minivan, state police said. All five people in the minivan were killed, including Regina Ayres, 24, and her two children, Jordan Ayres, 7, and Jonathan Ayres, 2 months. Regina's 30-year-old sister, Zerissa Ayres, who was expecting a child, also died. All of them were from Greenbush, Virginia. Travis Straton, 25, the father of Jonathan Ayres, also was killed. He was from Onancock, Virginia. The truck slammed into the car on the passenger side and rolled over on the vehicle before coming to rest. The Ayers were returning home from Baltimore where they had visited family. Police say there was no snow at the time of the crash, but that temperatures were extremely low. The cause of the crash remains under investigation, and no charges have been filed so far. Snow and cold temperatures played a part in Friday's massive 200-vehicle pile up in Michigan that took the life of one man and left 22 people injured. Four of the five were pronounced dead at the scene of the Maryland crash, police said. Zerissa Ayres, who was pregnant, was transported by ambulance to Easton Memorial Hospital, where both she and her unborn child were pronounced dead. The tractor trailer driver is identified as Yvenet Mayette, 28, of Wilmington, Delaware. He was flown by Maryland State Police helicopter to the University of Maryland Shock Trauma Center, where he is being treated for injuries.  The accident occurred around 1 a.m. Saturday in rural Wye Mills, about 60 miles (97 kilometers) east of Washington, D.C., when the two vehicles collided at an intersection on Route 50, according to police.