Obstetric anal sphincter injuries (OASIS), or third-degree and fourth-degree perineal tears, represent a serious complication at childbirth. The rate of OASIS for primiparous women in the United Kingdom has been reported to have increased from 1.8 to 5.9% over a twelveyear period 1 . In women who suffered OASIS at first birth, the incidence of a repeat OASIS has been shown to be 8.4% in hospital-based studies 2 and 7.2% in population-based studies 3 in the United Kingdom. In other countries, the rate of repeat OASIS in hospital-based and population-based studies has been reported to range widely from 2.0 to 7.2% 4,5 and from 5.6 to 7.1% 6,7 , respectively. Even though there are well defined risk factors for the occurrence of OASIS, such as nulliparity and instrument assistance at birth, the combination of these risk factors in different scoring systems does not allow the accurate prediction of OASIS 8 . Also, there have been only few interventions described that might reduce the risk of OASIS, such as 'hands-on' perineal protection at crowning 9-11 , the use of warm compressions during the second stage of labour and perineal massage during pregnancy 12 .Using a 5% average rate of OASIS means that 1/20 first time mothers will suffer severe trauma of their perineum at vaginal birth that cannot be predicted, while there are few available interventions, of yet unclear benefit, to reduce its occurrence at childbirth. Furthermore, the associated morbidity is significant to these women as OASIS is a prominent risk factor for the development of anal incontinence (AI) 13 , which is defined as the involuntary leakage of flatus or/and faeces 14 . Women who have sustained OASIS at birth have a two-fold to three-fold greater risk of developing subsequent AI 13 , with rates of AI ranging between 7 to 61% 15 . It has also been reported that 20 to 40% of women still described symptoms of AI at twelve months after birth 16 , with significantly increased risks of AI even after 15 years from childbirth 17 . In the case of long-term AI, there are additional factors that have been reported to aggravate the severity of bowel symptoms, such as age and menopause
17. Women who have sustained OASIS at first birth and have a subsequent second pregnancy are exposed to the risk of a repeat OASIS that has been well quantified in the literature 2,3 , and to the potential risk of developing AI that is still to be determined with ongoing research 18 . Even if a repeat OASIS does not occur in the second childbirth, symptoms of AI might still present as a consequence of cumulative pudendal neuropathy, prolonged second labour or even an instrumental delivery at second birth 18 . On the other hand, there are recent reports that the risk of developing long term AI is not associated with the second delivery but only with the severity of OASIS at first childbirth 19 . Moreover, an elective cesarean delivery at second pregnancy has been quoted not to be protective of AI even in cases of a fourthdegree perineal tear at first birth 19 . Most studies in t...