Perineal trauma after childbirth affects millions of women worldwide. Approximately 85% of women sustain some form of perineal trauma following vaginal delivery. Short and long-term morbidity associated with perineal repair can lead to major physical, psychological and social problems affecting the woman’s ability to care for her newborn baby and other members of the family. Perineal trauma may occur spontaneously during vaginal birth or when a surgical incision (episiotomy) is intentionally performed to enlarge the diameter of the vaginal outlet. Measures to reduce trauma to the lower genital tract, knowledge of anatomy of the pelvic floor and perineum, and techniques to repair trauma are integral components of obstetric care.
The overall risk of obstetric anal sphincter injury (OASIS) is 1% of all vaginal deliveries. However ‘occult’ OASIS (i.e. defects in the anal sphincter detected by anal endosonography) has been defined in 33% of primiparous women following vaginal delivery. The most plausible explanation for what was previously believed to be an occult OASIS is either an injury that has been missed, recognized but not reported or wrongly classified as a second degree tear. With increased awareness and focused training, the clinical detection of OASIS has increased. In centres where mediolateral episiotomies are practised, OASIS occurs in 1.7% (2.9% in primiparae) compared to 12% (19% in primiparae) in centres practising midline episiotomy.
The perineum corresponds to the outlet of the pelvis and is somewhat lozenge shaped. Anteriorly, it is bound by the pubic arch, posteriorly by the coccyx, and laterally by the ischiopubic rami, ischial tuberosities and sacrotuberous ligaments. The perineum can be divided into two triangular parts by drawing an arbitrary line transversely between the ischial tuberosities. The anterior triangle, which contains the external urogenital organs, is known as the urogenital triangle and the posterior triangle, which contains the termination of the anal canal, is known as the anal triangle . The muscles of the pelvic floor and perineum are shown in Figure 23-1 . The perineal body is composed of dense connective tissue to which is attached the bulbospongiosus muscle anteriorly, the superficial transverse perineal muscles laterally and the anal sphincter complex posteriorly. Also attached to the perineal body is the recto-vaginal septum and fascia. The anal sphincter complex consists of the external anal sphincter (EAS) and internal anal sphincter (IAS) separated by the conjoint longitudinal coat ( Figure 23-2 ). The IAS is a thickened continuation of the circular smooth muscle of the bowel.
In order to standardize definitions of perineal tears, the following classification is recommended:
First degree − injury to perineal skin only
Second degree − injury to perineum involving perineal muscles but not involving the anal sphincter
Third degree − injury to perineum involving the anal sphincter complex:
3a: Less than 50% of EAS thickness torn
3b: More than 50% of EAS thickness torn
3c: Both EAS and IAS torn
Fourth degree − injury to perineum involving the anal sphincter complex (EAS and IAS) and anal epithelium.
The traditional teaching that episiotomy was protective against more severe perineal lacerations has not been substantiated. Thus, the liberal use of ‘prophylactic’ episiotomy is no longer recommended. However, there are still valid reasons to perform an episiotomy:
To reduce the occurrence of multiple lacerations in the presence of a thick or rigid perineum.
To shorten the second stage in cases of fetal distress and where prolonged ‘bearing down’ may be harmful for the mother (e.g. severe hypertensive or cardiac disease).
In selected cases of assisted vaginal delivery with forceps and, less frequently, for vacuum assisted delivery. Although there is increasing evidence from observational studies that routine mediolateral episiotomy during instrumental delivery reduces the risk of third and fourth degree tears, there are no randomized trials.
To obtain more room for obstetrical manoeuvres such as those associated with shoulder dystocia, assisted breech delivery and delivery of the second twin.
‘It sometimes happens … that the head of the child … cannot however come forward by reason of the extraordinary constriction of the external orifice of the vagina … wherefore it must be dilated if possible by the fingers … if this cannot be accomplished, there must be an incision made towards the anus with a pair of crooked probe-scissors, introducing one blade between the head and the vagina, as far as shall be thought necessary for the present purpose and the business is done at one pinch, by which the whole body will easily come forth’.
A Treatise of Midwifery in Three Parts. Dublin: Nelson and Connor, 1742, p145
There are two main types of episiotomy:
Midline episiotomy . Two fingers are placed in the vagina between the fetal head and the perineum and, using straight scissors, the incision is made from the fourchette through the perineal body up to but not including the EAS. Advantages of the midline episiotomy are that it does not cut through the belly of the muscle, the two sides of the incised area are anatomically balanced making surgical repair easier, and blood loss is less than with mediolateral episiotomy. A major drawback is the propensity for extension through the EAS and into the rectum. For this reason many practitioners avoid the midline technique and it is not recommended in the UK.
Mediolateral episiotomy . The incision is made starting at the midline of the posterior fourchette and aimed towards the ischial tuberosity to avoid the anal sphincter. The incision is usually about 4 cm long. In addition to the skin and subcutaneous tissues the bulbocavernosus and the transverse perineal muscles are cut. Whether the incision is to the right or left depends on operator preference.
‘But sometimes it happens by an unlucky and deplorable accident, that the perineum is rent, so that the privity and fundament is all in one … Let it be strongly stitched together with three or four stitches or more, according to the length of the separation, and taking at each stitch good hold of the flesh, that so it may not break out …’
The Diseases of Women with Childbed and in Childbed. Translated by Hugh Chamberlen. London: John Darby, 1683, p316
Episiotomy and Second Degree Tears
The principles involved in repairing both episiotomies and second degree tears are similar. First, it is essential to assess the full extent of trauma by doing a vaginal and rectal examination. Unless this careful appraisal is carried out, partial or complete tears of the anal sphincter can be missed. Although the repair of these tears was previously carried out using the interrupted technique, the continuous suturing technique for perineal skin closure has been shown to be associated with less short-term pain. Moreover, if the continuous technique is used for all layers (vagina, perineal muscles and skin), the reduction in pain is even greater. The perineal muscles should be repaired using absorbable polyglactin material, which is available in standard and rapidly absorbable forms. A recent Cochrane review has shown that there are few differences in short-term and long-term pain, between standard and rapidly absorbing synthetic sutures but more women need standard sutures to be removed.
Using 2/0 absorbable polyglactin 910 material (Vicryl rapide ® ) the first stitch is inserted above the apex of the vaginal trauma to secure any bleeding points that might not be visible. The vaginal trauma is closed using a loose, continuous, non-locking technique making sure that each stitch is inserted not too wide, otherwise the vagina may be narrowed. Suturing is continued down to the hymenal remnants and the needle is inserted through the skin at the fourchette to emerge in the centre of the perineal wound ( Fig 23-3a ).