BOSTON — A Massachusetts mother stuck in traffic on the Massachusetts Turnpike has given birth to a baby girl.State police received a call from the baby's father at about 6:30 a.m. Friday. A police spokesman said the mother appeared to already be delivering the baby.The unidentified couple was headed eastbound near Natick.Police said that by the time two troopers and an ambulance arrived on the scene a few minutes after the call, a healthy baby girl had been born.