Obstetrical procedures include cesarean sections, episiotomies, and assisted delivery. During childbirth (unless by Cesarean section) the fetus passes through the maternal "pelvic opening". If repaired, subsequent pregnancies will require cesarean section. Obstetric fistulae are almost entirely preventable with appropriate use of cesarean section. Postpartum physiological changes may be different for women delivering by cesarean section. A uterine scar from a previous cesarean section is the most common risk factor. Therefore, many guidelines recommend against non-medically required induced births and elective cesarean before 39 weeks. After four cesarean sections, however, it affects 10% of pregnancies. Due to this complication, she delivered Wren three weeks early via elective cesarean section. "Womb raiding" and "cesarean or in utero kidnapping" are media terms for fetal abduction. Birth by Cesarean section or vaginal delivery also influences the gut's microbial composition. In 2011, 32.8 percent of births in the US were delivered by cesarean section. In February 2007, Simpson gave birth to a baby named Jacqueline via cesarean section. Rebecca sleeps through her contractions and her cesarean section. She suffered complete organ failure after delivering Alice from an emergency cesarean.