A scarred uterus is the biggest risk factor for a ruptured uterus. The types of scars that can cause a uterine rupture include the following:
- Scar from a C-section
- Hysterotomy scar. Hysterotomy is in incision in the uterus made during a C-section when the baby has shoulder dystocia (shoulder caught on mother’s pelvis).
- Uterine perforation scar. This can occur as a result of any complication involving the uterus and trans-cervical procedures.
- Myomectomy or metroplasty scar. These scars are from the removal of fibroids in the uterus.
- Scar from the previous repair of a ruptured uterus.
During pregnancy, imaging of scars should be performed. An intact, thick scar means the repair of the previous C-section or any other uterine surgery was likely pretty good. A thin scar or defect should cause the physician to worry about a possible uterine rupture during labor as well as during pregnancy.
Most uterine ruptures occur because a scar from a previous C-section is present. Some of these involve classical C-section scars, which are longitudinal (across the abdomen), upper segment scars. These scars can not only rupture during labor and delivery, but they can rupture during pregnancy as well. Rupture of lower segment C-section scars usually takes place during labor.
Other risk factors for uterine rupture include the following:
- Cephalopelvic disproportion (CPD). This is when the mother’s pelvis is too small for the size of the baby, resulting in the baby being unable to pass through the birth canal.
- Malpresentation. This is when the baby is not in the normal head-first position. Malpresentations include brow, face, breech and shoulder presentations.
- Grand multiparity. This is when the mother has given birth 5 or more times.
- Uncontrolled use of Pitocin (oxytocin), Cytotec or other labor induction drugs. This is probably the leading cause of rupture of the unscarred uterus. Pitocin can cause contractions to be too strong and too frequent, which puts a lot of strain on the uterus. A recent study found that in one medical center, Pitocin had been administered in 77% of their uterine rupture cases. The chance of Pitocin-induced rupture increases with women who have had previous traumatic births.
- Placental abruption. This is when the placental lining separates from the uterus. This can cause the baby to be either partially or completely cut off from the mother’s circulation.
- Multiple fetuses (twins, triplets, etc.)
- Post-term labor
- Operative deliveries. Using a delivery device, such as forceps or performing internal version, can cause uterine rupture. Internal version is when the physician inserts a hand into the womb and grasps the baby by one or both feet to turn her.
When Pitocin is used in the presence of other risk factors for uterine rupture, such as grand multiparity, malpresentation, or a previous C-section scar, it is extremely dangerous. In fact, using Pitocin when these conditions are present is contraindicated.
Experts emphasize that the best way to prevent uterine rupture is through prophylaxis; physicians must be aware of the mother’s past medical history and must closely watch her during pregnancy and labor. Great effort must be made in diagnosing even minor degrees of CPD or malpresentation, and in treating grand mutliparity and other risk factors, especially placental abruption. Mothers with risk factors should be attended to and treated in a special high-risk intensive care zone in the labor department by specially trained physicians and personnel. Difficult operative deliveries should not be attempted, and instead, delivery by C-section should take place.
A vaginal birth after C-section (VBAC) should be attempted only on a mother who has had a previous transverse, lower-uterine segment C-section for a non-recurring condition, and only after a very careful assessment has been made by the physicians with a determination that vaginal delivery would be favorable. Informed consent from the mother is crucial, and this involves discussing all the risks of a VBAC as well as the alternatives, such as a C-section delivery.