In the era of new molecular, epigenetic and proteomic discoveries, birth canal injuries seem like outdated discussion. A vast increase in the incidence of obstetric anal sphincter injuries (OASIS) has been recorded in the last two decades despite advantages in modern medicine and new obstetric methods. This increase might be attributed to the new classification of perineal injury but also to the new imaging methods, including endoanal sonography, which earlier identifies injuries that previously were considered to be occult and actually underwent unrecognized, and which should have been recognized immediately postpartum. OASIS are third and fourth degree perineal injuries that occur during delivery. The reported incidence of OASIS varies from 0.1% to 10.9%. It is well known that third and fourth degree perineal injuries occur more often in primiparae, and in cases of macrosomic newborn, dorsoposterior position of fetal head and shoulder dystocia. The protective role of episiotomy is controversial. Birth canal injury during delivery can happen to any parturient woman. It is important for obstetricians to have this in mind at every delivery. Repercussions of OASIS are serious and can persist for life. They include emotional, psychological, social, physical and sexual disturbances. Therefore, it is very important to recognize the risk factors, diagnose the injury on time and treat it properly by a multidisciplinary team. Accordingly, it can be concluded that the increased incidence of OASIS is a result of better recognition of the risk factors, reduced rates of unrecognized sphincter injuries, adoption of the new classification and better postpartum imagining methods for detection of occult injuries.
Keywords: Anal canal – injuries; Birth injuries; Delivery, obstetric – adverse effects; Perineum – injuries.