bed rest

so I went to the doctor this week and they had informed me that my baby was no longer growing her rate was only 27%and she was a bit small. so they put me on bed rest . well I know no one is doctor on this website but has this ever happen to anyone. I am already over 36 weeks so why not delive the baby. she weigh 5pd9oz and they said she will be perfect. then why keep her in there where she is no longer growing. any been tho this?