Several factors are associated with an increased chance of requiring episiotomy. The most common factor is nulliparity. This term refers to the condition of never having given birth before. Studies have reported that women having their first baby have an approximately 80% chance of vaginal laceration (episiotomy or tear) that will require repair. After a mother has successfully delivered a child vaginally, future deliveries will be less likely to cause vaginal trauma (because there has been some stretching of the vaginal tissue).
Another factor is the size of the baby. If the estimated weight of the baby is high, there is a greater chance episiotomy will be needed. Women who are at increased risk for shoulder dystocia, such as those who have diabetes, should have an episiotomy performed.
The position of the baby may also increase the chances that episiotomy will be required. If the baby's head is in a position other than the normal face down position (for example, if the baby is in a face-up or breech position) the need for episiotomy is increased. Women delivering more than one baby (such as twins or triplets) will more likely require an episiotomy than those who are delivering a single baby.