Obstetric anal sphicnter injury in a Spanish hospital

Estimation of the prevalence of obstetric anal sphincter injury (OASIS) in our environment and study of the associated risk factors.

A retrospective observational study of cases and controls of assisted deliveries at the Severo Ochoa University Hospital of Leganés during the period from January 1, 2012, to December 31, 2017. A total of 88 OASIS diagnosed in the study period is compared with a randomly selected group of 181 controls of similar characteristics, vaginal births of cephalic of 36 weeks gestation or more, occurring during the same period.

During the study period, a total of 8160 deliveries were attended in our hospital, of which 6187 were vaginal and we diagnosed a total of 88 OASIS at the time of delivery. The prevalence of OASIS is 1.07 % for total births and 1.42 % for total vaginal deliveries. In the case-control study, the univariate analysis shows statistical significance for nulliparity (OR 3.84; 95 % CI 2.155-6.834; p < 0.001), instrumental delivery (OR 8.73; 95 % CI 4.706-16.2016; p < 0.001), occipital posterior position (OR 7.23; 95 % CI 2.535-20.633; p < 0.001), long duration of the second stage of labor (OR 1.99; IC95 % 1,159-3,438; p 0.01), episiotomy (OR 3.51; 95 % CI 1,956-6,309; p < 0.001) and OBGYN labor assistant (<0.001). When performing the multivariate analysis, forceps delivery (OR19.68), Thierry spatulas delivery (OR 8.15), vacuum delivery (OR 2.74), nulliparity (OR 2.56) and fetal weight in grams (OR 1.12) remain significant in the final model.

The main risk factors for the onset of OASIS are instrumental delivery, nulliparity and fetal birth weight.