Objective: Anal sphincter injury and its sequelae are a recognized complication of vaginal childbirth. The aim of the present study was to identify risk factors for third- and fourth-degree perineal tears in patients undergoing either spontaneous or vaginal-assisted delivery by forceps routinely combined with mediolateral episiotomy.
Study design: We retrospectively reviewed 5377 vaginal deliveries based on the analysis of the obstetric database and patient records of our department during a 5-year period from 1999 to 2003. Cases and control subjects were chosen randomly and patients' records were reviewed for the following variables: maternal age, parity, gestational age, tobacco use, gestational diabetes or pregnancy-induced hypertension, use of peridural anesthesia, duration of first and second stages of labor, use of mediolateral episiotomy, forceps combined with mediolateral episiotomy, induction of labor, infant head diameter, shoulder circumference, and birth weight.
Results: Of 5044 spontaneous vaginal deliveries 32 (0.6%) and of 333 assisted vaginal deliveries 14 (4.2%) patients sustained a perineal defect involving the external sphincter. An univariate analysis of these 46 cases and 155 randomly selected control subjects showed that low parity (P = .003; Mann-Whitney U test), prolonged first and second stages of labor (P = .001, P = .001), high birth weight (P = .031), episiotomy (P = .004; Fisher exact test), and forceps delivery (P = .002) increased the risk for sphincter damage. In multivariate regression models, only high birth weight (P = .004; odds ratio [OR] 1.68, 1.18-2.41, 95% confidence interval [CI]), and forceps delivery combined with mediolateral episiotomies (P < .001; OR 5.62, 2.16-14.62, 95% CI) proved to be independent risk factors. There was a statistical significant interaction of birth weight and head circumference (P = .012; OR 0.99, 0.98-0.99, 95% CI). Although the use of episiotomy conferred an increased risk toward a higher likelihood of severe perineal trauma, it did not reach statistical significance (P = .06; OR 2.15, 0.97-4.76, 95% CI).
Conclusions: In consistence with previous reports, women who are vaginally delivered of a large infant are at a high risk for sphincter damage. Although the rate of these complications was surprisingly low in vaginally assisted childbirth, the use of forceps, even if routinely combined with mediolateral episiotomy, should be minimized whenever possible.