Sunday, June 9, 2024
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The risks associated with cesarean delivery can be divided into those that are short term, those that are longer term, and those that present risks to future pregnancies. There are also risks to the newborn that need to be considered. Certainly, the clinical situation that gives rise to the cesarean delivery has a great impact on the risk of complications. A primary cesarean section performed for an average-weight woman who is not in labor confers a much lower risk of complications than an emergency cesarean section performed on an obese woman who has chorioamnionitis and has been in labor for hours. Therefore, when comparing a trial of labor with a cesarean delivery, one must recognize that although there is a lower risk for many of the complications discussed below when the delivery is vaginal, the risks associated with a cesarean section performed in labor are greater than those associated with planned deliveries. In a similar vein, when interpreting studies of the risk of cesarean delivery one needs to consider that it may not be appropriate to compare women who delivered by cesarean with those who delivered vaginally. It may be more appropriate to compare those who had a trial of labor with those who had a planned cesarean delivery. After all, the counseling that a provider does in the prenatal period is not aimed at whether a patient should opt for a vaginal delivery or a cesarean section, but whether she wants to have a trial of labor or a planned cesarean delivery. Many of the studies cited below do try to separate women who had planned cesarean deliveries from those who underwent cesarean sections in labor in order for the reader to understand that there are certain increased risks for planned cesarean deliveries as well.
Maternal Death. The risk of maternal death during childbirth is greater with cesarean delivery compared with vaginal delivery, although very low.[3-6] A study that examined births between 1983 and 1992 in the Netherlands found that the risk of maternal death was 0.04 per 1000 vaginal births compared with 0.53 per 1000 cesarean deliveries; although the authors reported that the risk directly attributable to the actual cesarean delivery was 0.13 per 1000 births.[6] In this study, there were 57 deaths in the group of women who had delivered by cesarean and, of these, 10 were judged to be directly related to the surgery and 4 resulted from a complication of anesthesia. Further, in 16 of these cases, it was believed that the cesarean contributed to the death (eg, via thromboembolism or sepsis). These data do not distinguish between the different clinical situations that may contribute to the risk of maternal mortality. Additionally, while the relative risk of mortality may be significant, the increase in the absolute risk is quite small. The results of a study of postpartum mortality among primiparas in Washington State conducted between 1987and 1996 suggest that rather than a risk factor for death, cesarean delivery may be a marker for preexisting morbidities associated with increased mortality risk.[5]
Thromboembolism. One of the leading causes of maternal mortality related to cesarean delivery is deep vein thrombosis resulting in pulmonary embolism. Ros and colleagues[7] reviewed more than 1 million deliveries in Sweden from 1987 to 1995 and found that the relative risk of pulmonary embolism with cesarean delivery was approximately 7; after excluding women with preeclampsia, the increase in risk was 4-fold relative to vaginal delivery.
This is consistent with another study of nearly 400,000 births that found approximately 4-fold higher rate of deep vein thrombosis in women undergoing cesarean delivery as compared with vaginal delivery.[8] Other risk factors for thromboembolism are important to consider with cesarean delivery, as they may have additive risk for a given patient -- most importantly a history of thromboembolism and another factor that is more commonly encountered, maternal obesity.[9]
Hemorrhage. Blood loss during a cesarean delivery may be greater than during a vaginal delivery;[10,11] however, the transfusion rate remains low at 1% to 2% of patients undergoing cesarean section.[12] Planned cesarean deliveries have been associated with a lower risk of early postpartum hemorrhage compared with instrumental vaginal deliveries and unplanned cesarean deliveries in one population-based cohort study,[13] but in another population-based cohort study, no differences in excessive or prolonged bleeding were found between spontaneous vaginal deliveries and planned or unplanned cesarean deliveries at 3 postpartum time periods (8, 16, and 24 weeks).[14] Excessive blood loss during a cesarean section typically results from laceration of uterine vessels that occurs with extension of the uterine incision. Additional lacerations may extend into the vagina and result in significant bleeding and increased operative time. The risk of hemorrhage requiring blood transfusion increases substantially with increasing number of prior cesarean deliveries.[15]
Infection. Infection is one of the most common complications of cesarean delivery.[13,16,17] In the absence of prophylactic antibiotics, the rates of postpartum endomyometritis can be as high as 35% to 40%.[18] This rate varies dramatically according to the clinical situation, with rates as high as 85% for women undergoing cesarean section after an extended labor and as low as 4% to 5% for those undergoing a scheduled cesarean delivery with intact membranes.[18] The use of routine prophylactic antibiotics substantially reduces the rate of infection.[19]
Another common complication of cesarean delivery is wound infection. Wound infections may occur in 2.5% to 16% of cesareans.[20]
Incidental Surgical Injuries. Bladder injuries are the most common injuries to surrounding structures occurring at the time of cesarean delivery. Nevertheless, they are rare. Evaluating a series of nearly 15,000 cesarean deliveries, Phipps and colleagues[21] reported that bladder injuries were encountered in 0.28% of deliveries (0.14% for primary cesarean sections and 0.56% for repeat procedures).
Less common surgical injuries involve the bowel or ureters. Risk factors for any of these injuries are prior pelvic surgery (including prior cesarean deliveries), emergency cesarean delivery, and cesarean-hysterectomy. Early recognition and prompt management of these injuries are key to preventing the development of further complications, such as sepsis, renal failure, and fistula formation.
Extended Hospitalization. A woman who has had a cesarean delivery typically remains hospitalized longer than one who has had a vaginal delivery and has increased risk for readmission.[5,10,14] Patients who delivered abdominally are usually discharged on the 3rd or 4th postpartum day compared with the 1st or 2nd postpartum day for those who deliver vaginally. The average length of hospitalization may even be longer given some of the complications (eg, postpartum infections) that are more common in women who deliver by cesarean section.
Emergency Hysterectomy. The risk of the need for hysterectomy after or during a cesarean delivery is greater than after a vaginal delivery.[22-24] An important problem with any study that looks at this issue, however, is that they do not control for those women who had a trial of labor before their cesarean delivery. Thus, women undergoing a primary cesarean section who have not labored may have a lower rate of emergent hysterectomy than those who labored before their cesarean delivery.
One study attempted to mitigate this issue by performing a case-control study of women who had a hysterectomy postpartum (within 14 days of giving birth). Compared with a control group of women who did not have a hysterectomy, those who did have a hysterectomy were 13 times more likely to have been delivered by cesarean section after controlling for prior cesarean delivery, use of prostaglandins or oxytocin, and the use of magnesium sulfate.[22]
Pain. Women who undergo cesarean delivery more commonly experience pain after delivery compared with those having vaginal deliveries.[14,25-27] A study of 242 primiparous women reported that all those who underwent cesarean deliveries (both planned and unplanned) required narcotic pain medications compared with 11% of those who delivered vaginally.[17] Having to relieve pain with narcotic pain medications can have a significant impact on initial bonding between the mother and the newborn and on breastfeeding success rates, as well as maternal functioning postpartum; in addition, the risk for postpartum depression may be greater.[17,28,29]
Poor Birth Experience. In a meta-analysis of 43 studies published between 1979 and 1993, DiMatteo and colleagues[28] found that women who delivered healthy babies by cesarean section (both planned and unplanned) were more likely to report dissatisfaction with their birth experience compared with those who delivered vaginally.
Women who deliver by cesarean have less early contact with their newborns than those who deliver vaginally, and typically have to wait a significantly longer time before their first contact with their baby.[17,28,29] Women who deliver by cesarean are more likely to cite a poorer score for their initial contact with their baby.[30]
Readmission to the Hospital. In a study of more than 250,000 deliveries from Washington State, the rate of postpartum readmission to the hospital was significantly greater for those who delivered by cesarean delivery than for those who delivered vaginally (RR 1.8, CI 1.6-1.9), and this increased risk persisted even after controlling for obstetric and intrapartum complications.[31] Unfortunately, this study could not distinguish between planned and unplanned cesarean deliveries.
Pain. Women who undergo cesarean deliveries are more likely to report pain to be a problem in the first 2 months after delivery. A national survey of more than 1500 women who had delivered in the prior 24 months found that those who delivered by cesarean reported that incisional pain was a major problem 25% of the time, and a major or minor problem 83% of the time.[25] This was in contrast to the 12% of women who delivered vaginally and reported that perineal pain was a major problem, and a major or minor problem 44% of the time. This same study reported that at 6 months postpartum, 7% of women who delivered by cesarean continued to report that incisional pain was a problem compared with 2% of mothers who delivered vaginally and reported perineal pain.
Another study compared 116 patients undergoing laparoscopic evaluation for chronic pelvic pain with 83 asymptomatic women undergoing laparoscopic tubal ligation. Those with pelvic pain were 3.7 times more likely to have had a prior cesarean delivery.[27]
Adhesion Formation. Adhesion formation resulting from cesarean delivery is common and significantly contributes to the risk of complications at future deliveries (see below). Adhesions arising from cesarean deliveries can also on rare occasions contribute to other complications, such as small bowel obstruction. One study estimated that the risk was 0.5 per 1000 cesarean deliveries.[32]
These adhesions may also be contributing to the reported increased risk of ectopic pregnancy among women with prior cesarean deliveries.[33]
Infertility/Subfertility. An observational study of nearly 4000 women reported that women who had undergone cesarean delivery were more likely to be unable to conceive a pregnancy for more than 1 year (OR = 1.53, CI 1.09, 2.14).[34]
Neonatal Death. Although cesarean deliveries are typically performed for the benefit of the fetus, there are also risks for the newborn. In fact, a large observational study of more than 580,000 deliveries in California (that did not control for potential confounders) found that babies both born by planned as well as unplanned cesarean deliveries had a nearly 4-fold risk of dying before discharge compared with those delivered vaginally (8 deaths per 10,000 births for each planned or unplanned cesarean deliveries and 2 per 10,000 for those delivered vaginally).[35]
Respiratory Difficulties. Most well described are the respiratory difficulties encountered in newborns delivered at term. These respiratory difficulties, known as transient tachypnea of the newborn (TTN), probably result from a failure of the mechanisms to resorb fetal lung fluid that are typically triggered during vaginal birth. A review of nearly 30,000 births found that the incidence of TTN is about 3 times more common after elective cesarean delivery than after vaginal delivery (3.1% v. 1.1%, respectively).[36]
Asthma. Several studies have reported an association between cesarean delivery and the later development of asthma. One of these studies examined more than 40,000 children delivered by cesarean and found that those delivered either by planned or unplanned cesarean were approximately 30% more likely than those delivered vaginally to have been admitted to the hospital for asthma during childhood.[37] This increased risk of asthma may persist into adulthood. In a study of more than 9700 Danish women, the authors found that those who were delivered by cesarean were also approximately 30% more likely to report that they ever had asthma.[38]
Iatrogenic Prematurity. Also encountered more commonly with planned cesarean deliveries than those performed after the onset of labor is iatrogenic prematurity. This occurs occasionally even for babies thought to be full term, as was reported in a study of more than 170,000 births in England.[39]
Trauma. Babies delivered by cesarean are also at risk of trauma, most commonly as the result of surgical cuts, particularly during emergency deliveries. One recent study reported that the incidence of the lacerations was about 3%, although they were usually mild.[40]
Failure to Breastfeed. A meta-analysis of 9 studies found that babies delivered by cesarean were less likely to be breastfed compared with those who were delivered vaginally, and this effect seemed to be stronger for those delivered by unplanned cesareans.[28] Another study of more than 580,000 women in California found that mothers who underwent planned or unplanned cesarean deliveries were nearly twice as likely to have breastfeeding difficulties compared with those who delivered vaginally.[35]
The discussion of trial of labor and vaginal birth after cesarean vs repeat cesarean delivery is beyond the scope of this article. Clearly, all the risks of primary cesarean delivery are only increased for repeat cesareans, and increase even more with third, fourth, and higher-order cesarean deliveries. Some of these risks have been discussed earlier in this article. A trial of labor after a prior cesarean delivery confers its own risks, including the higher risks associated with a repeat cesarean delivery performed for a woman in labor.
Uterine Rupture. Although the risk of uterine rupture in the pregnancy subsequent to a cesarean delivery clearly relates to the mode of delivery in that subsequent pregnancy, even women who plan a repeat cesarean delivery have a greater risk of rupture than women with no prior cesarean deliveries. A population-based study of more than 255,000 women in Switzerland found that the incidence of uterine rupture for a woman with no previous cesarean delivery was 0.007%. That incidence rose to 0.192% for a woman with a prior cesarean delivery who planned a repeat cesarean delivery, and rose even higher to 0.397% for women who planned a trial of labor after a prior cesarean delivery.[41]
Abnormal Placentation. Evidence continues to accumulate that a prior cesarean delivery increases the risk of abnormal placentation in future pregnancies. A meta-analysis of observational studies that included a total of 3.7 million pregnancies found that women with at least 1 prior cesarean delivery had approximately 3 times the risk of having a placenta previa at the time of delivery compared with women with no prior cesarean deliveries, and this risk increased substantially with increasing numbers of prior cesarean deliveries -- reaching nearly 45 times the risk for women with 4 or more prior cesarean deliveries.[42]
Additionally, a prior cesarean delivery increases the risk of placenta accreta. This is particularly true for women with placenta previa. A study of 292 women with placenta previa found that those who had had a prior cesarean delivery were nearly 5 times more likely to have a placenta accreta compared with those with no prior cesarean deliveries (24% vs 5%, respectively).[43] Another study of more than 155,000 births in Los Angeles found that having 1 previous cesarean delivery increased the risk of placenta accreta more than 4-fold, and the relative risk of accreta for a woman with more than 2 prior cesarean deliveries rose to 11.32.[44]
Prior cesarean delivery may also be a risk factor for placental abruption in the next pregnancy. That risk compared with the risk for a woman with a prior vaginal delivery may be approximately an additional 30%.[45]
Hysterectomy. The increased incidence of accreta in patients with prior cesarean deliveries translates to an increased risk of hemorrhage and increased risk of cesarean hysterectomy. As the number of prior cesarean deliveries rises, the risk of cesarean hysterectomy increases dramatically. By the fourth cesarean delivery, the risk may be more than 2%.[15] All this may also contribute to a higher risk of maternal mortality with increasing number of prior cesarean deliveries.
