Trends in Major Risk Factors for Anal Sphincter Lacerations: A 10-Year Study

Abstract

Objectives: (1) To identify independent risk factors for analsphincter laceration. (2) to determine the trend in rates of analsphincter laceration over a 10-year period, and (3) to examinethe impact of temporal trends in risk factors on anal sphincterlaceration rates.Methods: Population-based data were obtained from the NovaScotia Atlee Perinatal Database. on 91 206 women who had asingleton vaginal live birth ≥500 g for the years 1988 to 1997.Risk factors for anal sphincter laceration were identified usingstepwise logistic regression. A multivariate model was used tostudy temporal changes in laceration rates after controlling forchanges in parity, episiotomy rates, operative vaginal deliveries,birth weight. prolonged second stage of labour, and other determinants.Results: Nulliparity (relative risk [RR] = 6.97), occiput posteriorposition (RR =2.44), non-vertex presentations (RR =2.27),second stage ≥ 120 min (RR range = 1.47-2.02), deliveryby an obstetrician (RR = 1.30), and birth weight ≥3000 g(RR range = 1.43-6.63) increased the risk of laceration.Instrument-assisted delivery involved risks that ranged from a2-fold increase for a vacuum-assisted delivery (RR =2.15) to agreater than 5-fold increase for a forceps delivery after anunsuccessful vacuum extraction (RR = 5.69). Episiotomy,particularly midline incisions, increased the risk of laceration(RR =2.57). The risk of a sphincter laceration increased 2-foldfrom 1988 to 1997. despite controlling for risk factors.Conclusions: Sufficient evidence exists about the risk factors foranal sphincter laceration to permit modification of managementof labour and delivery to minimize the risk of anal sphincterlaceration. Increased awareness of the c1inical importance ofrecognition and repair of anal sphincter laceration may explainthe rising incidence.