Keywords

1 Introduction

Spontaneous delivery is considered to be a risk factor for anorectal dysfunction, through pregnancy and injuries induced by labor and delivery to the pelvic floor muscles, the rectovaginal septum, the anal sphincter complex and the pudendal nerve. In the last few years, the demand for cesarean section has increased for several reasons, including the conviction that it can prevent the development of problems of the maternal pelvic floor. In this chapter we will analyze the impact of the mode of delivery on the perineal plane.

The anorectal canal is surrounded by a complex bundle of muscle fibers that make up the external and internal sphincters. The striated muscles of the external sphincter are subject to voluntary control and are responsible for the tone that keeps the rectal canal narrow. The smooth muscles of the internal sphincter, on the other hand, keep the tone at rest and are responsible for moment-to-moment fecal continence. The two muscle groups overlap at a distance of 2 cm and extend upward in the canal for 4 cm. The outer sphincter is inserted on the central perineal tendon and is surrounded by the puborectalis muscle.

Although both sphincters are important for maintaining continence, it has been shown that laceration of the external sphincter has greater impact on the anal sphincter.

The classification of lacerations validated by the Royal College of Obstetricians and Gynaecologists (RCOG) considers four degrees (Fig. 16.1) [1]. Third-degree lacerations include partial or complete laceration, with or without laceration of the internal sphincter, while fourth-degree lacerations include complete laceration of both sphincters, with extension to the rectal mucosa. Anal continence does not entirely depend on sphincter integrity, as neuromuscular function, the puborectalis muscle and the pudendal nerve also play a role.

Fig. 16.1
A diagram of the anal sphincter muscles. A wide opening is a rectum that opens into the anus, it has the number4 marked on it. The rectum is lined by longitudinal muscle on the left, which has 3b and 3c marked on both sides, and smooth muscles on the right. The thick muscles lining the anus are labeled internal anal sphincter which is marked 3b.

Diagrammatic representation of the anal sphincters demonstrating the Sultan classification of major degrees of perineal tears (3a, 3b, 3c, and 4). Reproduced from [1] with permission from Springer

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Lacerations of the anal sphincter are classified further into “clinically recognizable” and “occult”. The former are identified and repaired at the time of delivery, while the latter, which are typically diagnosed by ultrasound, may occur below an intact perineum or in the presence of second- or first-degree lacerations [2].

2 Anal Incontinence and Mode of Delivery

Anal continence is a complex physiological mechanism that depends on factors such as intestinal disorders and habits, cortical awareness, integrity of the pelvic floor muscles and anal sphincter muscles in particular, as well as a number of psychological factors.

Anal incontinence is associated with advanced age, obesity, pregnancy, operative delivery, and obstetric lacerations of the anal sphincter. In addition to anal incontinence, laceration of the anal sphincter can also cause fecal urgency, perineal pain, and sexual dysfunction.

Anal incontinence, defined as “the involuntary loss of air or liquid and solid stools that constitutes a social and hygienic problem”, occurs in 15–59% of women with anal sphincter lacerations repaired at the time of delivery. Fecal urgency afflicts another 6–28% of women. Fecal incontinence, the loss of liquid or formed feces, is less frequent, occurring in 2–23% of cases. These symptoms may appear as a result of clinically recognizable or occult laceration [3].

No association between anal incontinence and delivery mode was shown by comparing women who had undergone cesarean sections and those who had a vaginal delivery [4]. However, when spontaneous childbirth is complicated by injuries to the anal sphincter, anal incontinence is tripled. In addition, both forceps and suction cups increase the risk of pelvic floor dysfunction. According to recent studies, women who had induction of labor with oxytocin, and in whom the neonatal head circumference is 34 cm or more, are significantly more at risk of developing anal incontinence and should be closely monitored after delivery.

Part of the complex physiological mechanism of continence may be compromised by injury to the muscles of the anal sphincter, and if one or more risk factors are needed during labor, their combination can potentially have a synergistic impact on the development of anal incontinence after childbirth and in the long term [5]. In addition, spontaneous delivery has been associated with an increase in the number of injuries to the levator ani muscle, increased mobility of the bladder neck and an enlargement of the genital hiatus, laying the foundations for the development of urinary incontinence and prolapse [6]. Maternal expulsive efforts during delivery and the force uterine contractions exert on the fetal head can induce stretching and compression of the pelvic floor nerves, which may lead to ischemia, neurapraxia or compromised nerve function. It is believed that nerve injury during delivery can result in muscle atrophy, hence altering pelvic floor function and morphology. The degree of muscular distension may lead to either a lesion or avulsion, which is associated with enlargement of the genital hiatus after delivery.

Factors not associated with delivery include advanced age, obesity, severity of disorders such as diarrhea and constipation, level of education and fecal urgency [7]. The effects of aging include reduced rectal compliance, reduced rectal sensitivity, perineal laxity, and delayed post-traumatic healing.

Among the factors associated with delivery, parity, operative delivery and macrosomia (birth weight of 4000 g of the first child) significantly increase the risk of anal sphincter injury and are more related to the development of long-term anal incontinence [8].

In severe lacerations, the five most important factors are: median episiotomy; use of forceps or obstetric cup; Asian ancestry; high weight at birth; first delivery.

Compared with vaginal delivery, cesarean delivery is associated with higher maternal and infant mortality, higher levels of complications in subsequent pregnancies, increased perinatal mortality, placenta previa or ectopic pregnancy, as well as higher health costs; hence, its recommendation, on the basis of its potential protective effect on the pelvic floor, is controversial and continues to arouse scientific debate [9].

There is conflicting evidence on the benefits of cesarean section in the prevention of postpartum anal incontinence [10]. Some studies suggest that the timing of a cesarean section, particularly when this is practiced in advanced labor, may have an impact on the mechanisms of continence.

Although cesarean section showed a protective effect on short-term anal incontinence, 6 months after delivery there is no longer a significant association between the mode of delivery and the development of anal incontinence. Nonetheless, it is essential to identify pregnant women with a higher risk of early anal incontinence after labor. In fact, although most cases of anal incontinence resolve within 6 months of delivery, even a short symptomatic period can negatively affect the quality of life of a young mother [11].

In conclusion, cesarean section does not appear to have a protective effect against the development of anal incontinence, in either the short or long term [12]. However, when vaginal delivery is operative or complicated by anal sphincter injury, the risk is significantly increased [13]. When anal incontinence occurs in old age and in obese woman it is more associated with factors independent of the mode of delivery [14]. Given that anal incontinence is still poorly reported due to social reasons, it is important to identify its risk factors, as early rehabilitation performed immediately after childbirth has been shown to reduce, and possibly prevent, anal incontinence later in life.

3 Conclusions

In conclusion, despite evidence of an increased risk of developing incontinence and pelvic organ prolapse following vaginal delivery, the recommendation of an elective cesarean section with the sole purpose of preserving the maternal pelvic floor should be taken with caution, as there is no direct evidence about the protective effect of elective cesarean section [15].

Although women with sphincter lacerations report more incontinence than those without lacerations, the symptoms increase in both groups with subsequent vaginal deliveries. The risk of sphincter lacerations during a second delivery increases by two to five times in women who had previous lacerations, compared to those with no history of clinically recognizable laceration [16]. Recurrence is greatest when the second delivery is vaginal or when episiotomy (especially median) is performed. A subsequent vaginal delivery also affects the severity of incontinence symptoms. However, because not all studies support the conclusion that subsequent deliveries contribute to anal incontinence, it is reasonable to ask whether the increases in anal incontinence are due to the large number of vaginal deliveries or to other influences such as age.

As regards occult lacerations, there may be an indication to perform ultrasound for the diagnosis and to proceed to immediate repair. Therefore, it is important to document the appearance of symptoms of transient or permanent anal incontinence after delivery. Ultrasound evaluation of the anal sphincters together with manometry can be indicated in all incontinent women.

During counseling, women should be informed of the increased risk of new lacerations in subsequent vaginal deliveries. Continent women are less likely to develop incontinence than those who previously had symptoms of transient or persistent anal incontinence. These outcomes are aggravated by episiotomy and operative delivery, which increase the risk of new lacerations and subsequent anal incontinence.

It is unclear whether the long-term symptoms after reiterated vaginal delivery in women with previous sphincter lacerations are different from those of women with no history of lacerations, and the issue should be investigated.

In summary, women with a history of anal sphincter lacerations during the first vaginal delivery are more likely to develop new lacerations and heightened incontinence symptoms with a subsequent one. Operative delivery and episiotomy (especially median) should be avoided because they aggravate the risk of further damage in all these women.

After a detailed discussion about the risks and benefits of attempting a new vaginal delivery, an election cesarean section may be considered in women with symptoms of anal incontinence [16].