Emergency crews responded to Robbins Road near the 172nd Avenue intersection at about 11:40 a.m.
Two westbound vehicles were stopped for a red light when the second one was struck from behind and pushed into the first vehicle, according to a Grand Haven public safety officer.
The drivers of the second and third cars were taken to the hospital for observation of possible injuries.
Police said a 35-year-old Muskegon woman suffered an unknown medical condition prior to the crash. An ambulance transported her to a Muskegon hospital.
The driver of the middle vehicle, a 19-year-old pregnant woman from Grand Haven, was also taken to the Muskegon hospital for unknown injuries.
The driver of the first vehicle that had stopped for light, a 25-year-old Muskegon woman, was not injured.
Robbins Road was closed while crews worked at the scene. The eastbound lane was re-opened to traffic shortly after noon. The westbound lane was cleared by about 12:30 p.m.