Third- or Fourth-Degree Intrapartum Anal Sphincter Tears Are Associated With Levator Ani Avulsion in Primiparas.

OBJECTIVES: We evaluated primiparous women with clinically diagnosed third- and fourth-degree and anal sphincter tears, to evaluate the rate of levator ani muscle injury compared to primiparous women without sphincter tears.
METHODS: Primiparous women delivering in our maternity ward with intrapartum diagnoses of third- or fourth-degree anal sphincter tears, repaired by the overlapping technique, were recruited to undergo 3-dimensional transperineal sonography of the pelvic floor anatomy, including the anterior and posterior compartments. Primiparas with uncomplicated vaginal deliveries were recruited as a comparison group. Patient files were examined, and maternal backgrounds and delivery and neonatal details were extracted for all patients.
RESULTS: Ninety-four women with tears were recruited to the study group, and 464 women with normal vaginal deliveries constituted the comparison group. The groups differed significantly in the rates of levator ani defects: 38 of 94 women (40.4%) in the study group versus 75 of 464 (16.2%) in the comparison group (P < .001; odds ratio, 3.53; 95% confidence interval, 2.18–5.7). Neonatal head circumference differed significantly between the study and comparison groups: (mean ・} SD, 34.5 ・} 1.3 cm in the study group versus 33.9 ・} 1.3 cm in the comparison group; P= .005), as did birth weight (3322 ・} 430 g in the study group versus 3169 ・} 458 g in the comparison group; P= .007). The groups did not differ in maternal age, gestational age at delivery, length of second stage of labor, and rates of epidural anesthesia, episiotomy, and vacuum extraction.
CONCLUSIONS: Third- and fourth-degree intrapartum sphincter tears are associated with levator ani avulsion. Knowledge of complex pelvic floor damage may allow for prompt referral to secondary preventive measures for pelvic floor disorders.