Yesterday I shared a Canadian article, and last year a letter from two OBs opposing a hospital VBAC ban, which discuss the risks of cesarean sections including placenta accreta and hysterectomy.

Definitions

Today I want to share a study that measured the increasing risks that come with multiple cesareans, but before I do so, lets do a quick review of definitions.

Placenta accreta (March of Dimes 2005):

In a normal pregnancy, the placenta attaches itself to the uterine wall, away from the cervix.

• Placenta accreta is a placenta that attaches itself too deeply and too firmly into the wall of the uterus.
• Placenta increta is a placenta that attaches itself even more deeply into the uterine wall.
• Placenta percreta is a placenta that attaches itself through the uterus, sometimes extending to nearby organs, such as the bladder.

Hysterectomy (Women’s Health 2009):

A hysterectomy (his-tur-EK-tuh-mee) is a surgery to remove a woman’s uterus or womb. The uterus is where a baby grows when a woman is pregnant. The whole uterus or just part of it may be removed. After a hysterectomy, you no longer have menstrual periods and cannot become pregnant.

Placenta previa (PubMedHealth 2011):

Placenta previa is a complication of pregnancy in which the placenta grows in the lowest part of the womb (uterus) and covers all or part of the opening to the cervix.

There are different forms of placenta previa:

• Marginal: The placenta is next to cervix but does not cover the opening.
• Partial: The placenta covers part of the cervical opening.
• Complete: The placenta covers all of the cervical opening.

The risks of placenta accreta, cystotomy [surgical incision of the urinary bladder], bowel injury, ureteral [ureters are muscular ducts that propel urine from the kidneys to the urinary bladder] injury, and ileus [disruption of the normal propulsive gastrointestinal motor activity], the need for postoperative ventilation, intensive care unit admission, hysterectomy, and blood transfusion requiring 4 or more units, and the duration of operative time and hospital stay significantly increased with increasing number of cesarean deliveries.

Accreta was defined as the “placenta being adherent to the uterine wall without easy separation [and] included placenta accreta, increta, and percreta.”

Below are some slides from the VBAC Class I developed and teach illustrating the  rates of placenta accreta, previa, previa with accreta, and hysterectomy by number of cesareans (Silver 2006).   The number below the cesarean number indicates how many women were included in that category.

Remember as you look these over, the risk of uterine rupture in a spontaneous labor after one prior low horizontal (“bikini-cut”) cesarean is 0.4% (Landon 2004).  Risk of uterine rupture during one’s second cesarean is 0.9% (Landon 2006).

Accreta, previa, and cesarean hysterectomies

I was especially interested to see the relationship between previa and accreta.  Silver (2006) found that if you have previa, you are very likely to have accreta and that risk increases with each cesarean.  For example, if a woman has one cesarean and is diagnosed with previa in her next pregnancy, her risk of having accreta is 11%.  That risk jumps to 40% in the third pregnancy, 61% in the fourth pregnancy and 67% for the fifth and sixth pregnancy.

Complications associated with accreta

Accreta is nothing to mess around with as it has a very high rate of maternal mortality (up to 7%) and morbidity including hemorrhage and hysterectomy.  Fang (2006) asserted, “abnormal adherent placentation [is] the primary indication leading to emergent peripartum hysterectomy…. As the number of prior cesarean deliveries rises, the risk of cesarean hysterectomy increases dramatically.”   In other words, all these primary cesareans and repeat cesareans are causing placentas to abnormally implant in subsequent pregnancies.  As a result, many women who have placenta accreta end up having hysterectomies as that is the best way to control the hemorrhaging that results from accreta.

Women who had accreta also experienced the following complications:

• 15.4% (1 in 6.5): surgical injury to bladder
• 2.1%  (1 in 48): surgical injury to the ureters which are the tubes that connect the kidneys to the bladder and is the “most serious complication of gynecologic surgery“
• 2.1%  (1 in 48 ): blockage of an artery in the lungs (pulmonary embolism)
• 14% (1 in 7):  mom was put on a mechanical ventilator because she couldn’t breathe effectively
• 26.6% (1 in 3.8): mom requires advanced monitoring and care so she is admitted to the intensive care unit
• 5.6% (1 in 17.8): mom requires another operation
• 3.5% (1 in 28.6): endometritis, “an inflammation or irritation of the lining of the uterus”

Because the risks of cesarean are so great, Silver (2006) concluded with the following statement,

Because serious maternal morbidity increases progressively with increasing number of cesarean deliveries, the number of intended pregnancies should be considered during counseling regarding elective repeat cesarean operation versus a trial of labor and when debating the merits of elective primary cesarean delivery.

Evidence to suggest previa less likely to “move” in VBAC/VBAMC moms

RCOG’s clinical guidelines also included evidence that of women who were diagnosed with previa early in their pregnancy, women with a prior cesarean where less likely than an unscarred mom to have their placenta “move” enough to permit a vaginal delivery at term (50% vs. 11%).  Since the study in question included over 700 women with previa, this is a large enough study to give us good evidence.

Women with a previous caesarean section require a higher index of suspicion as there are two problems to exclude: placenta praevia and placenta accreta.  If the placenta lies anteriorly and reaches the cervical os at 20 weeks, a follow-up scan can help identify if it is implanted into the caesarean section scar.

Placental ‘apparent’ migration, owing to the development of the lower uterine segment, occurs during the second and third trimesters,52–54 but is less likely to occur if the placenta is posterior55 or if there has been a previous caesarean section.35  In one study, only five of 55 women with a placenta reaching or overlapping the cervical os at 18–23 weeks of gestation (diagnosed by TVS) had placenta praevia at birth and in all cases the edge of the placenta had overlapped 15 mm over the os at 20 weeks of gestation.56  A previous caesarean section influences this: a large retrospective review of 714 women with placenta praevia found that even with a partial ‘praevia’ at 20–23 weeks (i.e. the edge of the placenta reached the internal cervical os), the chance of persistence of the placenta praevia requiring abdominal delivery was 50% in women with a previous caesarean section compared with 11% in those with no uterine scar.53

Conversely, although significant migration to allow vaginal delivery is unlikely if the placenta substantially overlaps the internal os (by over 23 mm at 11–14 weeks of gestation in one study,54 by over 25 mm at 20–23 weeks of gestation in another52 and by over 20 mm at 26 weeks of gestation in a third study57), such migration is still possible and therefore follow-up scanning should be arranged.

I looked up source 53 and it’s Dashe (2002) which shared:  “The outcome of the study was persistent placenta previa resulting in cesarean delivery.  This diagnosis was based on clinical assessment and ultrasound at time of delivery.”  You can read Dashe in its entirety by clicking on this link and then looking for the “Article as PDF” link on the right hand side.

Considering your future fertility

Many women who don’t plan on having more children do not think these complications are applicable.  But I know many women, and I’m sure you do too, who were not planning on more children, but got pregnant nonetheless.  This is consistent with the CDC’s findings that 49% of pregnancies are unintentional.  Unless you or your partner get sterilized or practice abstinence (what fun!), the chance of you getting pregnant, and experiencing these downstream risks, are there.  It’s important when evaluating your current birth options to consider how that decision will impact the risks of your future pregnancies as well as your future delivery options.

Last updated 9/13/12.