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Best Evidence: VBAC or Repeat C-Section


Best evidence: When making important maternity decisions, women should have information from the best available research about the safety and effectiveness of different choices. In general, we can be most confident about results of systematic reviews that summarize randomized controlled trials (or RCTs, a type of study).

Unfortunately, for many decisions we must rely on less definitive research; and many important questions even in the case of widely used drugs, tests and procedures have hardly been studied at all. Although this situation is discouraging, an awareness of weak or missing evidence can help you make informed choices about care.

What is the bottom line?

What are some concerns about risks of c-section compared with vaginal birth?

What are some concerns about risks of vaginal birth compared with c-section?

What are some ways that a planned c-section may differ from an unplanned c-section?

What is the added likelihood that the scar will give way (uterine rupture) during a VBAC labor?

What is the added likelihood that the baby will die as a result of the scar giving way (uterine rupture) during a VBAC labor?

What is the added likelihood of the scar giving way (uterine rupture) with any of the following factors listed below?

What is the added likelihood of the scar giving way (uterine rupture) with twin pregnancy or the use of external cephalic version (turning a baby in a buttocks- or feet-first (breech) position to a head-first position by manipulating the woman's belly)?

What is the added likelihood that a woman planning VBAC will require a hysterectomy compared with a woman planning repeat c-section?

What is the added likelihood that a woman will require a hysterectomy as a result of the scar giving way (uterine rupture) during a VBAC labor?

What is the added likelihood that a woman will develop an infection after a planned cesarean?

What are some concerns about effects of accumulating uterine scars on future pregnancies and births?


This page presents results of recent systematic reviews that can help women compare risks of planned vaginal birth after cesarean (VBAC) and of planned c-section (see references at end of page). While more high-quality studies are needed, a large body of research already exists and sheds light on these questions for those who need guidance now.

When deciding whether to plan a VBAC or a repeat cesarean, it is important to understand the full range of risks to you and your baby. This means comparing the short- and long-term risks of cesarean surgery and risks of accumulating cesarean surgery scars to mothers and babies on the one hand, to the risk that the uterine scar will give way (uterine rupture) and lead to problems and a few risks that are worse for vaginal birth generally.

Even if you do not plan to have more children, you should be aware of risks of multiple cesarean scars to future pregnancies and babies. Many women change their mind and decide to become pregnant again or continue with unplanned pregnancies.

What is the bottom line?

If you do not have a clear and compelling need for a cesarean in the present pregnancy, having a VBAC rather than a repeat c-section is likely to be:

  • safer for you in this pregnancy
  • far safer for you and your babies in any future pregnancies

When thinking about the welfare of your baby in the present pregnancy, there are trade-offs to consider: VBAC has some advantages, and a repeat c-section has others. You can learn more below.

KEY MESSAGES ABOUT VBAC VS. REPEAT CESAREAN SECTION:

See details about scar-related effects after the following summary lists.

Despite limitations of the best available research, the following conclusions seem clear:

  • Scar giving way: The scar is more likely to give way during a VBAC labor than in a repeat c-section; for most women (exceptions noted below), the added risk of the scar giving way is about 27 in every 10,000 VBAC labors. In other words, nearly 400 women would need to experience the risks involved with repeat c-section to prevent one uterine rupture during a VBAC labor.
  • Death of baby: While the scar giving way poses a threat to the baby, the added risk that the baby will die from a problem with the scar during a VBAC labor, compared with women planning repeat c-sections, is about 1.4 in every 10,000 VBAC labors. In other words, over 7100 women would need to experience the risks involved with repeat c-sections to prevent the death of 1 baby due to uterine rupture.
  • Hysterectomy in mother: If the scar gives way, some women have a hysterectomy (removal of the uterus). The added risk of needing a hysterectomy from this cause is about 3.4 in every 10,000 VBAC labors, when compared with women planning repeat c-sections. However, considering risk for hysterectomy from all causes, women who plan a VBAC are not more likely to experience an unplanned hysterectomy than women planning repeat c-section.
  • Concerns about specific risks: The following factors do not increase risk of the scar giving way during labor:
    • type of uterine scar not known
    • low vertical uterine incision for prior c-section (may have been used if c-section was performed earlier in pregnancy before growth in lower part of the uterus)
    • baby estimated to be large, and to weigh more than 4,000 grams (8 pounds, 13 ounces)
    • pregnancy goes past 40 weeks.
  • Concerns about other risks: The following factors have not been shown to increase the risk of the scar giving way, but too few cases have been studied to be confident:
    • twin pregnancy
    • use of external cephalic version: turning a baby who is positioned buttocks- or feet-first (breech) to head-first position by manipulating the woman's belly
  • Infection: Women planning c-sections are more likely to develop infections than women planning VBACs.
  • Multiple scars in uterus: Accumulating c-section scars increase risk for experiencing a number of serious problems relating to future pregnancies and births. These include:
    • scar rupture in a subsequent labor
    • ectopic pregnancy: the embryo develops outside the uterus
    • placenta previa: the placenta grows over the cervix, the opening to the uterus
    • placental abruption: the placenta separates from the uterus before the baby is born
    • placenta accreta the placenta growing abnormally into or even through the uterus.

What are some concerns about risks of c-section compared with vaginal birth?

When weighing planned VBAC versus planned c-section, the focus is often on potential problems with the uterine scar in labor or on problems associated with accumulating scars. But this results in an incomplete picture because it overlooks other risks that also differ between vaginal birth and cesarean section. Summarized here are some of the many extra risks associated with cesarean surgery as well as the few advantages. (In Best Evidence: C-Section, you can find a detailed comparison of risks of cesarean and vaginal birth, including how likely these problems are to occur.)

Most of what we know about these risks comes from studies of cesarean in general, not planned c-section. Available research suggests that some of these risks may be lessened when the c-section is planned. The next question: What are some ways that a planned c-section may differ from an unplanned c-section? points to adverse effects where research finds differences in risk.

As you consider these, keep in mind that on average, 3 out of 4 women who labor after a c-section will give birth vaginally with care that encourages and supports VBAC (and fewer than 1 in 100 will experience the scar giving way). Even in cases where women scored 0 to 2 on a scale where 10 indicated greatest likelihood of vaginal birth, half gave birth vaginally.

  • Physical problems for mothers: Compared with vaginal birth, cesarean section increases a woman's risk for a number of physical problems. These range from less common but potentially life-threatening problems, including hemorrhage (severe bleeding), blood clots, and bowel obstruction (due to scarring and adhesions from the surgery), to much more common problems such as longer-lasting and more severe pain and infection. Even after recovery from surgery, scarring and adhesion tissue increase risk for ongoing pelvic pain and for twisted bowel.
  • Hospital stays: If a woman has a c-section, she is more likely to stay in the hospital longer and to be re-hospitalized.
  • Emotional well-being: A woman who has a c-section may be at greater risk for poorer overall mental health and some emotional problems. She is also more likely to rate her birth experience poorer than a woman who has had a vaginal birth.
  • Mother-baby relationship: A woman who has a c-section is more likely to have less early contact with her baby and initial negative feelings about her baby.
  • Breastfeeding: Recovery from surgery poses challenges for getting breastfeeding under way, and a baby who was born by c-section is less likely to be breastfed and get the benefits of breastfeeding.
  • Impact on babies: Babies born by c-section are more likely to:
    • be cut during the surgery (usually minor)
    • have breathing difficulties around the time of birth
    • experience asthma in childhood and in adulthood.
  • Impact on any future babies: A cesarean section in this pregnancy increases risk for babies in future pregnancies. Some research finds that babies who develop in a scarred uterus are more likely to:
    • be born too early (preterm)
    • weigh less than they should (low birth weight)
    • have a physical abnormality or injury to their brain or spinal cord
    • die before or shortly after the birth

What are some concerns about risks of vaginal birth compared with c-section?

C-section offers advantages in a few areas, primarily during the recovery period after birth. (Some practices used with vaginal birth, such as episiotomy, are associated with pelvic floor problems. It is wrong to conclude at this time that vaginal birth itself causes such problems. See the Pregnancy Topic Preventing Pelvic Floor Dysfunction.

  • A woman who has a vaginal birth is more likely to:
    • have a painful vaginal area in the weeks after birth
    • leak urine (urinary incontinence) (about 3 women per hundred still have a problem 1 year after birth)
    • leak gas, or more rarely, feces (bowel incontinence) (about 3 women per hundred still have a problem 1 year after birth)
  • Babies born vaginally have been shown to be at higher risk for a nerve injury affecting the shoulder, arm, or hand (brachial plexus injury) (usually temporary).

What are some ways that a planned c-section may differ from an unplanned c-section?

A planned c-section offers some advantages over an unplanned c-section that occurs after labor is under way. For example, there is a lower risk of surgical injuries and of infections. The emotional impact of a cesarean that is planned in advance appears to be similar to or somewhat worse than a vaginal birth. By contrast, unplanned cesareans can take a greater emotional toll. In addition, a woman planning repeat cesarean surgery would almost certainly be less likely to experience difficulty breastfeeding if she had breastfed before or to have negative feelings for her baby compared with a first-time mother having an unplanned cesarean. Nonetheless, a planned cesarean still involves the risks associated with major surgery. And both planned and unplanned cesareans result in a uterine scar, which increases risk for serious concerns for mothers and babies in future pregnancies, and for adhesion-relation problems in mothers at any time.

To learn more about these differences, see

  • Best Evidence: C-Section for a summary of research comparing cesarean and vaginal birth.
  • Preventing Pelvic Floor Dysfunction for in depth information about the relationship between giving birth and a woman's pelvic floor health
  • details below about effects of giving birth when a woman's uterus has a scar from a previous cesarean

MORE DETAILED INFORMATION ABOUT SCAR-RELATED RISKS NOTED ABOVE

Click below on HIGH, MODERATE, etc. to understand difference in level of risk between care options.

What is the added likelihood that the scar will give way (uterine rupture) during a VBAC labor?

Best research suggests that an extra 27 women experience a ruptured uterus in every 10,000 VBAC labors, compared with planned c-section deliveries. Thus, nearly 400 women would need to experience surgical birth to prevent one instance of uterine rupture during VBAC labors. While the scar giving way usually requires an urgent cesarean, loss of the baby is much less common (see next paragraph).
Added likelihood for a woman with a known low-transverse (horizontal) scar: MODERATE for scar rupture compared with planned repeat c-section.

What is the added likelihood that the baby will die as a result of the scar giving way (uterine rupture) during a VBAC labor?

Best research suggests that about 1.4 extra babies die due to problems with the scar in every 10,000 VBAC labors, compared with planned c-section deliveries. Thus, over 7,000 women would need to experience risks of surgical birth to prevent the death of 1 baby from scar problems during VBAC.
Added likelihood for a woman with a known low-transverse (horizontal) scar: LOW for death of the baby around the time of birth compared with repeat c-section.

What is the added likelihood of the scar giving way (uterine rupture) with any of these factors:
  • type of uterine scar not known
  • low vertical uterine incision at prior c-section (may have been used if c-section took place earlier in pregnancy before growth in lower part of the uterus)
  • baby estimated to be large, weighing over 4,000 grams (8 lb 13 oz) or
  • pregnancy extends past 40 weeks?

Some caregivers recommend planned repeat c-section with these factors on the grounds that VBAC is riskier, but the research does not support that belief. More detailed information on these issues can be found in Options: VBAC or Repeat C-Section.
No added likelihood for scar rupture in a woman with unknown type of uterine scar, prior low vertical uterine incision, baby estimated to weigh more than 4,000 grams, or pregnancy extending past 40 weeks, in comparison with women planning VBAC without these factors.

What is the added likelihood of the scar giving way (uterine rupture) with twin pregnancy or the use of external cephalic version (turning a baby in a buttocks- or feet-first (breech) position to a head-first position by manipulating the woman's belly)?

While studies have not found an excess incidence of scar rupture in these situations, not enough women have been studied to rule out an increase. More detailed information on these issues can be found in Options: VBAC or Repeat C-Section.
No currently known added likelihood for scar rupture in a woman with a twin pregnancy or a woman experiencing external version, in comparison with women planning VBAC without these factors.

What is the added likelihood that a woman planning VBAC will require a hysterectomy compared with a woman planning repeat c-section?

Most studies find an excess of hysterectomies (surgical removal of the uterus) among women planning repeat c-section. However, this could be because those studies may have included cases where the c-section was planned for reasons that could increase the risk of complications during surgery such as the placenta overlaying the cervix (placenta previa). A study that took care to exclude women having planned repeat cesareans for medical reasons found no difference in the percentages of women having hysterectomies.
No apparent added likelihood for hysterectomy for a woman planning VBAC compared with a woman planning repeat c-section.

What is the added likelihood that a woman will require a hysterectomy as a result of the scar giving way (uterine rupture) during a VBAC labor?

Best research suggests that about 3.4 extra women have a scar-related hysterectomy (surgical removal of uterus) occurs in every 10,000 VBAC labors, compared with planned c-section deliveries. Thus, nearly 3,000 women would need to experience surgical birth to prevent one instance of hysterectomy due to scar problems during VBAC labors.
Added likelihood for a woman with a known low-transverse (horizontal) scar: LOW for hysterectomy as a result of uterine rupture compared with repeat cesarean.

What is the added likelihood that a woman will develop an infection after a planned cesarean?

Surgery always introduces the risk of infection. Even though some women who plan VBAC will have repeat c-sections, most will not. This puts women planning VBAC at lower risk of having an infection than women planning repeat c-sections.
Added likelihood for a woman planning repeat cesarean: MODERATE for developing a wound or internal infection compared with planned VBAC.

What are some concerns about effects of accumulating uterine scars on future pregnancies and births?

The likelihood of the following problems grows as the number of previous cesareans (and c-section scars) grows:

  • placenta previa: a woman whose uterus has a cesarean scar is more likely than a woman with an unscarred uterus to have a future placenta attach near or over the opening to her cervix; this increases her risk for serious bleeding, shock, blood transfusion, blood clots, planned or emergency delivery, emergency removal of her uterus (hysterectomy), placenta accreta (see next), and other complications.
    Added likelihood for a woman with a previous cesarean: MODERATE for placenta previa in a future pregnancy after having one cesarean; HIGH for placenta previa in a future pregnancy after having more than one cesarean
  • placenta accreta: a woman whose uterus has a cesarean scar is more likely than a woman with an unscarred uterus to have a future placenta grow through the uterine lining and into or through the muscle of the uterus; this increases her risk for uterine rupture (see below), serious bleeding, shock, blood transfusion, emergency surgery, emergency removal of her uterus (hysterectomy), and other complications.
    Added likelihood for a woman with at least one previous cesarean: MODERATE for placenta accreta in a future pregnancy, with increasing risk as the number of previous cesareans grows
  • rupture of the uterus: a woman whose uterus has a cesarean scar is more likely than a woman with an unscarred uterus to have the uterine wall give way in a future pregnancy or labor, especially at the site of the scar; this increases her risk for severe bleeding, shock, blood transfusion, blood clots, planned or emergency cesarean delivery, emergency removal of the uterus (hysterectomy), and other complications; whether a woman plans a repeat cesarean or a VBAC (vaginal birth after cesarean), she is at greater risk for a ruptured uterus than a woman with no previous cesarean.
    Added likelihood for a woman with a previous cesarean: MODERATE for rupture of the uterus, with increasing risk for two or more cesareans

Questions About Impact of Repeated Cesareans

We did not find research to clarify whether some scar-related risks in future pregnancies increase as the number of previous cesareans increases. The following risks for mothers are worse after one cesarean and may or may not grow as the number of c-section scars grow: fertility problems, ectopic pregnancy (not within the uterus), and placental abruption (placenta detaches before birth). The following risks for babies are worse after one cesarean and may or may not grow as the number of c-section scars grows: being born too early (preterm), being born too small (low birthweight), having a physical abnormality or injury to the brain or spinal cord, and dying before birth (stillbirth) or shortly after birth.

Scarring and adhesion tissue often increase as the the number of cesareans increases, creating greater and greater challenges for any future surgical procedures in the area. We did not find information to clarify whether the likelihood of the following adhesion-related problems grows as the number of cesareans grows: ongoing pelvic pain and risk for twisted and blocked bowel in women.

References

Guise J-M, Berlin M, McDonagh M, Osterweil P, Chan B, Helfand M. Safety of vaginal birth after cesarean: a systematic review. Obstet Gynecol 2004;103:420-9.

Guise J-M, McDonagh MS, Osterweil P, Nygren P, Chan BKS, Helfand M. Systematic review of the incidence and consequences of uterine rupture in women with previous caesarean section. BMJ 2004;329:159-65.

Hashima JN, Eden KB, Osterweil P, Nygren P, Guise J-M. Predicting vaginal birth after cesarean delivery: a review of prognostic factors and screening tools. Am J Obstet Gynecol 2004;190:547-55.

Lieberman E. Risk factors for uterine rupture during a trial of labor after cesarean. Clin Obstet Gynecol 2001;44:609-21. [Alone among references, this article is not a systematic review; it is included, however, as a well done review that addresses important questions for women facing the VBAC/repeat c-section decision.]

Childbirth Connection. Comparing risks of cesarean and vaginal birth to mothers, babies, and future reproductive capacity: a systematic review. New York: Childbirth Connection, April 2004. [The following study documents are available as PDF files from the Childbirth Connection website: description of methods and sources (including full bibiliography), list of main questions and outcomes (a table of contents for evidence tables), first file of evidence tables, and second file of evidence tables.]
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Tips & Tools: VBAC or Repeat C-Section
Most recent page update: 3/23/2006
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Childbirth Connection is a national not-for-profit organization founded in 1918 as Maternity Center Association. Our mission is to improve the quality of maternity care through research, education, advocacy and policy. Childbirth Connection promotes safe, effective and satisfying evidence-based maternity care and is a voice for the needs and interests of childbearing families.
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