A hospital spokeswoman said the woman was still in a critical condition on Saturday morning.
The spokeswoman could not say how heavily pregnant the woman was for privacy reasons.
She was also the driver of one of the vehicles, the spokeswoman said.
Two patients were taken to North Shore Hospital by ambulance.
The crash, which happened about 4pm, closed State Highway 1 between Wellsford and Warkworth for nearly four hours.
Bill Calthrop, whose wife owns the Top of the Dome cafe said the crash happened about 275m north of the cafe.
"A truck has hit a pickup truck. The sound of the collision woke me up," he said.