What About Uterine Scar Ruptures?

What is a uterine scar rupture?

A complete uterine rupture is a tear through the thickness of the uterine wall at the site of a prior cesarean incision. It is a potentially life threatening condition for both the mother and/or the baby and requires immediate surgical intervention. However, uterine ruptures have also been known to occur in some women who have never had a cesarean. This type of rupture can be caused by weak uterine muscles after several pregnancies, excessive use of labor inducing agents, prior surgical procedure on the uterus, or mid-pelvic use of forceps.

How often does a cesarean scar rupture occur?

For women who had a prior cesarean birth the rupture can occur at the site of the previous uterine scar. Dozens of studies report that for women who have had one prior cesarean birth with a low-horizontal incision, the risk of uterine rupture is about 1% or less.  A woman who has had more than one cesarean with a low horizontal incision may have a slightly higher risk of rupture.

Sometimes a woman may have “T” or “J” shaped scar on the uterus or one that resembles an inverted “T”. These scars are very rare. It is estimated that between 4 and 9% of “T” shaped uterine scars are at risk for rupture.

Medical experts state that the risk of a uterine rupture with one prior low-horizontal incision is not higher than any other unforeseen complication that can occur in labor such as fetal distress, maternal hemorrhage from a premature separation of the placenta or a prolapsed umbilical cord. Any birthing facility equipped to respond to a medical emergency in labor can care for women laboring for a VBAC.

Some women have a low vertical incision on the uterus, made when there is a placenta previa (low-lying placenta), a large baby, a baby in a transverse position (lying horizontally in the pelvis) or a premature breech delivery. When planning a VBAC it is important to determine if the previous low vertical scar has not stretched to the body of the uterus in the current pregnancy. The risk of rupture for a low vertical scar has been reported to be the same as for a low horizontal scar and as high as 1-7%.

Rarely, a woman may have a classical (vertical) scar in the upper part (the body) of the uterus. This type of incision is used for babies who are in a breech or transverse position, for women who may have a uterine malformation, for premature babies or in extreme circumstances when time is of the essence.

The risk of rupture for this type of scar has been reported to be between 4 and 9%. A classical scar on the thinner and more vulnerable part of the uterus tends to rupture with more intensity and result in more serious complications for mothers and babies. Mothers who have had several children and have a classical uterine scar are at higher risk for uterine rupture.

The American College of Obstetricians and Gynecologists and the Society of Obstetricians and Gynaecologists of Canada recommend that women with a classical scar have a repeat cesarean birth.

What are the symptoms of a uterine rupture?

A uterine rupture cannot be accurately predicted or diagnosed before it actually occurs. It can occur suddenly during labor or delivery. A few studies have suggested that measuring the thickness of the scar by ultrasound or following closely the pattern of contractions in labor may be useful in anticipating and therefore preventing a scar rupture. However, there is not enough information to prove that these methods should be widely adopted.

Several symptoms have been identified, but do not necessarily occur with every uterine rupture. Signs of uterine rupture that may or may not be present.

Vaginal bleeding

Sharp pain between contractionsContractions that slow down or become less intenseAbdominal pain or tendernessRecession of the fetal head (baby's head moving back up into the birth canal)Bulging under the pubic bone (baby’s head has protruded outside of the uterine scar)Sharp onset of pain at the site of the previous scarUterine atony (soft muscles)

To date, studies have shown that a uterine rupture can be detected by electronic fetal monitoring because the women in these studies laboring for a VBAC were monitored electronically. Although some caregivers closely monitor VBAC labors with a fetoscope or a hand-help ultrasound measuring device , (the Doppler) no  VBAC studies have yet been published on this method.

Abnormal fetal heart tones, variable decelerations, or bradycardia (slow heart rate) have been associated with a uterine rupture.

It is important to note that with a uterine rupture, labor sometimes continues, there is no loss of uterine tone or amplitude of contractions.

What happens if the scar ruptures?

Although uterine scar ruptures for women laboring for a VBAC are rare, the medical response is  a rapid cesarean. Studies show that when a surgical team responds quickly mothers and babies do well. Birthing facilities vary in their guidelines and protocols for VBAC and response time to uterine rupture or to any other unforeseen complication of labor.

Most guidelines allow for a maximum response time of 30 minutes. However, at least one US study reported better outcomes when the response time was 18 minutes or less. The longer it takes to respond to a uterine rupture the more likely it is that the baby and/or the placenta can be pushed through the uterine wall and into the mother’s abdominal cavity.

Women who receive good prenatal care, whose care providers are trained and experienced with VBAC, and who labor in a facility that is equipped to provide immediate medical care usually have good outcomes.

Women who are thinking about laboring for a VBAC at home may want to consider and make plans for the rare possibility of a uterine rupture.

Women thinking about laboring for a VBAC in a free-standing birth center may also want to ask about transport protocols in the rare event of a uterine rupture.

References:

To find out more about VBACs in accredited birth centers in the USA contact the National Association of Childbearing Centers at www.birthcenters.org.

For additional information see:
Birth After Cesarean, a consumer guide book by Bruce L. Flamm, MD., published in 1990 by Prentice Hall.
Cesarean Section Guidelines: Appropriate Utilization, a medical text book edited by Bruce L. Flamm, MD and E.J. Quilligan, MD. The text was published in 1995 by Springer-Verlag.
The Society of Obstetricians and Gynaecologists of Canada, Clinical Practice Guidelines Policy Statement: Vaginal Birth After Previous Cesarean Birth (no.68, December 1997).
American College of Obstretricians and Gynecologists. Vaginal Birth After Previous Cesarean Delivery Practice Guigelines (1999).