Rupture of the uterine scar and VBAC

The most rare yet most serious risk of vaginal birth after caesarean (VBAC) is that the scar on the uterus may break open (rupture) during labour. This is a rare risk whenever a woman has a scar on her uterus, but it is a little more likely to happen with a VBAC than a scheduled caesarean.¹

• About 5 out of every 1,000 women (0.5%) with one low side-to-side incision scar have a uterine rupture during VBAC when the labour starts on its own without the use of medicine.
• About 2 out of every 1,000 women (0.2%) with a low side-to-side scar who choose a scheduled repeat caesarean have a uterine rupture.

It is likely that the women who have a rupture have other risk factors that make them more likely to have to this complication.

Having had a vaginal delivery during another pregnancy lowers the risk of uterine rupture during VBAC. Women who have delivered vaginally and later had a caesarean delivery have about one-fourth the risk of women who have had a caesarean delivery but no vaginal delivery.²

A woman's risk of uterine rupture increases with:

• Each additional uterine surgical scar. A uterine rupture occurs in up to 8 out of 1,000 women with one scar. Up to 37 out of 1,000 women with two scars develop a rupture.³
• The use of medicine to start (induce) labour. Use of misoprostol (Cytotec) or oxytocin (Pitocin) to start (induce) labour has been linked to an increased risk of uterine rupture during VBAC. In one study, uterine rupture occurred in:¹
  • About 25 out of 1,000 women who were induced with misoprostol.
  • About 8 out of 1,000 women who were induced with oxytocin.
  • About 5 out of 1,000 women who had a spontaneous labour.
  • About 2 out of 1,000 women who had a planned repeat caesarean without labour.
  Some doctors avoid the use of any medicine to start a VBAC trial of labour. Other doctors are comfortable with the careful use of oxytocin to start labour when the cervix is soft and opening (dilating).
• Any uterine scar tissue that reaches above the lower, thinner part of the uterus. Between 40 and 90 out of 1,000 women with a vertical incision develop a rupture.²

Sparing use of oxytocin to help (augment) a slow labour has rarely been linked to uterine rupture.⁴ Some doctors also place a thin tube with a small balloon into the cervix. This can soften the cervix and does not seem to raise the chance of uterine rupture.

In the rare event that a uterine scar ruptures, it can be dangerous to both the mother and her infant. Depending on severity, a rupture can:

• Cause severe maternal bleeding and a decrease in oxygen to the baby.
• Often be repaired. If it is not repairable, the uterus is removed (hysterectomy).
• Cause fetal brain damage or death.
• Be mild and harmless.

Author:	Kathe Gallagher, MSW Carrie Henley	Last Updated: June 18, 2007
Medical Review:	Joy Melnikow, MD, MPH - Family Medicine Kirtly Jones, MD - Obstetrics and Gynecology
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