Pelvic Floor Trauma in Childbirth

Abstract

Between 4 and 40% of women will suffer permanent pelvic floor trauma in childbirth. Irreversible damage to the pelvic floor at the time of vaginal birth may take the form of trauma to the levator ani complex or obstetric anal sphincter injury (OASI). Long-term sequelae include pelvic organ prolapse, its recurrence after surgical repair, urinary and fecal incontinence, sexual dysfunction and chronic pelvic pain. Detection rates are poor, especially for levator ani trauma, which is often clinically undetectable at the time of vaginal birth. Translabial ultrasound is an objective method for the diagnosis of irreversible pelvic floor trauma and was used in observational studies for this thesis. Original studies undertaken for this thesis showed antenatal risk factors for levator avulsion include increasing maternal age (OR 1.05, p=0.019), lower body mass index (BMI; OR 0.94, p=0.018), and increasing bladder neck descent (BND; OR 0.97, p=0.026). Intrapartum risk factors identified include longer second stage (OR 1.02, p=0.01), OASI (OR 3.2, p= 0.002), and the use of forceps (OR 2.9, p=0.001). The latter is by far the strongest modifiable risk factor and should be avoided. Predictors of atraumatic normal vaginal delivery were younger maternal age (OR 0.93, p<0.001) and earlier gestation at delivery (OR 0.78, p=0.001), which is relevant to family planning. Overall, rates of atraumatic normal vaginal delivery in our population were much lower than generally assumed at 33-40%. An in vitro study showed that the predicted effect of forceps on avulsion risk is not explained by an increase in space requirement alone. It is likely that the main factor determining the traumatic potential of forceps is increased force over time, i.e., the characteristics of the pull exerted by the operator. Finally, it was found that conversion of a primary vacuum to a forceps delivery would result in an overall increase in major pelvic floor trauma from 31% to 39% of primiparas (p=0.018). Current trends towards the use of forceps to reduce Caesarean section rates are likely to result in an inadvertent increase in rates of levator avulsion and OASI. As current methods of anal sphincter repair and surgery for pelvic organ prolapse have high rates of failure, good obstetric care should emphasize the prevention of pelvic floor trauma at the time of a woman’s first birth.