A main question regards how episiotomy is performed, because it has a fundamental influence on anatomical structures that can be involved not only directly during the episiotomy itself, but also as regards the possibility of vaginal tears in other areas: this fact can occur if vaginal introitus is not enlarged enough by episiotomy to allow the passage of the fetus without creating other lesions, or if the incision is involuntarily widened creating a damage in the deeper structures. We must remember that the three variations of episiotomy are medial, a midline incision from the fourchette toward the anal canal, mediolateral, that begins at the midline and is directed laterally reaching an angle between 40° and 60° to the left or to the right of the anal canal, and lateral in which the incision begins laterally from the midline at 4–5 or 7–8 o’clock.

Following the classification and standardization of episiotomies published by Kalis et al. in 2012 [12], they can therefore be distinguished by type, origin of the initial incision and direction of the cut. Therefore, in every patient, the point of origin in relationship with the posterior fourchette, the angle from the midline, the length of the cut and the distance from the anal canal ought to be calculated (Fig. 9.1).

In the vast majority of obstetrical wards, only the midline and the mediolateral incisions are used.

The right way in which it must be performed (midline versus mediolateral) is a key point and is widely debated: for example, Coat et al. [13] reported that midline episiotomy was followed by anal laceration in 11.6 % of women, while only 2 % experienced such complication after mediolateral episiotomy. Other authors reported that the OR for complete lacerations after midline episiotomy ranged between 1.08 and 22 in spontaneous vaginal deliveries [14–16]. Studies evaluating the episiotomy technique showed that the angle is significantly associated with OASIS: Injuries occurred more frequently when the angle is inferior to 40° [17, 18].

In a very sophisticated study, Stedenfeldt et al. [19] in 2012 examined two groups of women who had had episiotomy or not as regarded the occurrence of OASIS: they showed that the risk of sphincter laceration decreased by 70 % by each 5.5 mm. increase in episiotomy depth, and by 56 % for every 4.5 mm increase in the distance from the midline.

Despite that, midline episiotomy is still widely performed because it appears more physiologic; it is considered easier to heal and is reported to cause less perineal pain or long-term dyspareunia. In our opinion, midline episiotomy should be almost abandoned, as it may be very dangerous: it has to be performed only by well-trained midwives, in non-operative deliveries and with fetuses with normal weight.

We must underline that the timing of episiotomy is also very important, as it must be done before the occurrence of any nervous stretching or anal sphincter disruption.

Even for this point, opinions are often different. In 2008, Murphy et al. [20] reported about the effects of routine versus restricted use of episiotomy in operative vaginal delivery, in a randomized trial, but their results, regarding 317 operative vaginal deliveries, were inconclusive: they did not find any evidence that routine episiotomy was better than a restrictive one in preventing 3rd or 4th degree tears; anal sphincter tears were 8.1 % with routine episiotomy in comparison with 10.9 % with restrictive use: No statistical difference was reached, but this result was probably negative because their samples were too small.

On the other hand, a larger retrospective study published by deLeeuw et al. [21] in 2008 showed that episiotomy appeared highly protective against anal sphincter tears both in forceps and in vacuum births: they demonstrated that the risk of anal incontinence after a complete perineal tear was lower if the patient had a mediolateral episiotomy (12 % vs. 46 %): this fact could be related also to the protective effect against neurological lesions.

The same opinion was expressed by de Vogel et al. [22]: in a very large study, they found that when MLE was performed, the risk of developing OASIS after operative vaginal delivery was decreased by sixfold (3.3 % vs. 15.6 %).

These dramatic differences may be related to different clinical behaviours in the timing of episiotomy or to its technique or indeed to the classification of anal tears. The comparison among the three studies underlines that the argument is not well clarified and that many confounding elements may contribute to different results, but the vast majority of authors agree that a MLE must be performed in operative vaginal deliveries. As a matter of fact, in order to prevent anal sphincter tears, a strict cooperation between the doctor and the midwife is required during operative delivery to ensure the best perineal support and the right timing of episiotomy.

It is well known that vaginal birth represents the major cause of anal incontinence (AI): even if lacerations of anal sphincter are uncommon, they represent a major complication of delivery with high percentages of subsequent faecal incontinence and/or defecatory problems: as a matter of fact, the incidence of AI following 3rd or 4th degree tears is reported as ranging from 7 to 56 %. We have already underlined that undoubtedly median episiotomy is to be considered at higher risk of anal sphincter tear, as reported even in recent studies [19]. The damage of anal sphincter can be due both to a direct lesion, eventually not completely sutured after delivery, and/or to denervation, following stretching or laceration of pudendal nerve terminations. Beginning from the studies of Snooks et al. in the 80s [23], denervation of the pelvic floor after vaginal delivery was fully demonstrated in about 80 % of women.

Stretching to pudendal nerve can lead to cumulative damages to pelvic floor, so that muscular denervation, atrophy, fibrosis and finally impaired function and defective organ support usually follow. As a matter of fact, up to 25 % of primiparous women experience small degrees of AI post-partum and one third show some aspects of anal sphincter injury. In most women, faecal incontinence resolves spontaneously, but at the age of 65 it affects about 13 per 1,000 women.

The study performed by Casey et al. [24] involving 10,643 primiparous women showed that episiotomy represented an odd factor for post-partum anal incontinence (OR 1.7) and for any type of urinary incontinence (both urge and stress types).

Other authors reported that after instrumental vaginal delivery the risk of anal incontinence is increased with an OR of 1.94–7.2; the risk of urinary incontinence appears to be increased with an OR of 1.81, while the frequency of urgency is increased of 4.2 times [21, 22].