The cause of preterm birth is often not known.[1] Risk factors include diabetes, high blood pressure, being pregnant with more than one baby, being either obese or underweight, a number of vaginal infections, tobacco smoking and psychological stress, among others.[2][3] It is recommended that labor not be medically induced before 39 weeks unless required for other medical reasons.[2] The same recommendation applies to cesarean section.[2] Medical reasons for early delivery include preeclampsia.[9]