Third- and fourth-degree perineal tears among primiparous women in England between 2000 and 2012: time trends and risk factors

Objective: To describe the trends of severe perineal tears in England and to investigate to what extent the changes in related risk factors could explain the observed trends.

Design: A retrospective cohort study of singleton deliveries from a national administrative database.

Setting: The English National Health Service between 1 April 2000 and 31 March 2012.

Population: A cohort of 1 035 253 primiparous women who had a singleton, term, cephalic, vaginal birth.

Methods: Multivariable logistic regression was used to estimate the impact of financial year of birth (labelled by starting year), adjusting for major risk factors.

Main outcome measure: The rate of third-degree (anal sphincter is torn) or fourth-degree (anal sphincter as well as rectal mucosa are torn) perineal tears.

Results: The rate of reported third- or fourth-degree perineal tears tripled from 1.8 to 5.9% during the study period. The rate of episiotomy varied between 30 and 36%. An increasing proportion of ventouse deliveries (from 67.8 to 78.6%) and non-instrumental deliveries (from 15.1 to 19.1%) were assisted by an episiotomy. A higher risk of third- or fourth-degree perineal tears was associated with a maternal age above 25 years, instrumental delivery (forceps and ventouse), especially without episiotomy, Asian ethnicity, a more affluent socio-economic status, higher birthweight, and shoulder dystocia.

Conclusions: Changes in major risk factors are unlikely explanations for the observed increase in the rate of third- or fourth-degree tears. The improved recognition of tears following the implementation of a standardised classification of perineal tears is the most likely explanation.