title: Incidence and Risk Factors of Obstetric Anal Sphincter Injuries after Various Modes of Vaginal Deliveries in Chinese Women.
abstract: BACKGROUND
  Obstetric anal sphincter injuries (OASIS) can cause an adverse impact on women's physical and mental health. There was lack of published data in Chinese population particularly on studying the risk of OASIS for nonrotational outlet forceps. This study was to determine the incidence and risk factors of OASIS.
  
  
  METHODS
  This is a retrospective cohort study carried out in a tertiary referral hospital in Hong Kong. The control group was selected randomly. Univariate and multivariate logistic regression analysis was performed to evaluate the influence of potential risk factors on OASIS. This study reviewed the obstetric records of OASIS women and random control from January 2011 to June 2014. Univariate and multivariate logistic regression analysis was performed to evaluate the influence of potential risk factors on OASIS.
  
  
  RESULTS
  Of 15,446 women delivered, 49 had OASIS. The percentage of OASIS increased from 0.3% (2011) to 0.38% (2014). There was an increasing trend of OASIS in attempted spontaneous vaginal delivery without episiotomy (P < 0.01), but it did not increase the OASIS risk (P = 0.46). Univariate analysis of 49 cases and 438 control subjects showed that forceps delivery (odds ratio [OR] =8.73, P < 0.01), prolong second stage of labor (OR = 1.43, P < 0.01) increased the risk for OASIS. In multivariate regression models, only forceps delivery (OR = 6.28, P < 0.01) proved to be independent risk factor.
  
  
  CONCLUSIONS
  The incidence of OASIS in Chinese women was increased after 2012, but still lower than the reported figures in the literature. Outlet forceps delivery could be a possible associated risk factor.
authors.affiliation: Department of Obstetrics and Gynaecology, Queen Elizabeth Hospital, Hong Kong, China.
authors.forename: Chi Wai
authors.initials: CW
authors.lastname: Tung
authors.forename: Willy Cecilia
authors.initials: WC
authors.lastname: Cheon
authors.forename: Wai Mei Anny
authors.initials: WM
authors.lastname: Tong
authors.forename: Hau Yee
authors.initials: HY
authors.lastname: Leung
mesh_terms: D000328:Adult; D001003:Anal Canal / Q000293:injuries*; D036861:Delivery, Obstetric / Q000009:adverse effects; D005260:Female; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D022125:Lacerations / Q000453:epidemiology* / Q000209:etiology*; D015999:Multivariate Analysis; D007744:Obstetric Labor Complications / Q000453:epidemiology* / Q000209:etiology*; D011247:Pregnancy; D012189:Retrospective Studies; D012307:Risk Factors