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Cesarean Section: Why?
by Marjorie Greenfield, M.D.
reviewed and revised by Marjorie Greenfield, M.D.
Sometimes cesarean is a planned, scheduled event, done for an expected reason, such as breech presentation or risk of uterine rupture. More often, the need for a c-section only becomes clear after labor is already underway. This can be a surprise for all involved.
Even if you are expecting a vaginal birth, it is a good idea to familiarize yourself with indications for cesarean, so you will feel less shocked if it comes up. The rate of cesarean at some hospitals is as high as 35%. Even under the best of circumstances, no one can guarantee that a cesarean won't be necessary.
Situations when a cesarean might be necessary:
- The baby isn't fitting through the birth canal
Causes of this include a large baby or a small pelvis, or poor contraction strength. The most common cause is a change in the baby's position, such that he presents a larger diameter of his head to the birth canal and doesn't fit through. For example, it may be something as simple as the baby's head being tipped to one side. This explains why a woman can need a cesarean for one baby and subsequently fit a larger baby through without problems. Technical terms for the reasons in this category include failure to progress in labor, arrested active phase, failure of descent, and cephalo-pelvic disproportion (CPD.)
- Placenta previa
Placenta previa (where the placenta lies across the internal opening of the cervix) may be diagnosed at the time of routine ultrasound or if there is vaginal bleeding in the second or third trimester. If the placenta continues to cover the cervical opening(also called the internal os of the cervix), cesarean is necessary to safely deliver the baby.
- Previous cesarean
There was a time when doctors lived by the dictum "Once a cesarean, always a cesarean." When that rule was established, cesareans were less common, and involved a large vertical incision in the uterus that created a weak spot right where the contractions were strongest. The risk of uterine rupture (the scar in the uterus popping open) during a subsequent pregnancy was significant.
Nowadays, most cesareans are done crossways, in the lower, less contractile part of the uterus. In these "low transverse" cesareans, the risk of uterine rupture is low, and most physicians believe that vaginal birth after cesarean (VBAC) is a safe option, maybe even safer than repeat cesarean.
Note that the incision in the skin may not go the same direction as the incision in the uterus, and it is the uterine incision that determines the risk of uterine rupture.
- The baby isn't coming head first
Breech babies (coming bottom-first instead of head-first) are often delivered by cesarean section, depending on technical considerations including the baby's size and position of the baby's legs and head, and the obstetrician's experience with vaginal delivery of breech babies.
Cesarean is always done if the baby is in transverse lie (lying sideways in the uterus) because this position is associated with significant risk of complications if the baby is born vaginally, including injury to the baby or cord prolapse.
- Infections in the birth canal
Cesarean is often done to protect the baby if the mother has active genital herpes, or other infections, like human immuno-deficiency virus (HIV), which can be transmitted during delivery.
- The baby needs to be delivered quickly
Emergency delivery can be necessary in fetal distress, in umbilical cord prolapse, in some cases of placental abruption or occasionally if the mother is seriously ill.
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Created September 25, 2000
Reviewed and revised April 14, 2003
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