Twenty-eight-year-old Jennifer Jorgensen was eight months pregnant when she crashed last week on a winding road in Ridge. Suffolk County police say she had crossed the road's center line.
The 74-year-old man driving the other car was killed. His 70-year-old wife was badly injured and is hospitalized in critical condition.
Jorgensen underwent a Caesarean section at a hospital in Stony Brook shortly after the May 30 crash.
Her newborn daughter had been in the hospital's neonatal intensive care unit. Police say she died Wednesday evening.
Jorgensen is listed in serious but stable condition.