Objective: To determine
which maternal characteristics or birth events independently predict severity
of levator ani muscle (LA) tears at first vaginal birth in a
longitudinal/observational investigation in a tertiary care hospital. Sample:
Ninety primiparas with at least
one at risk for LA tear inclusion factor at vaginal birth: maternal age ≥ 33
years, second stage ≥ 150 minutes, macrosomia, instrumented delivery, and/or
anal sphincter laceration were studied. Methods: Magnetic Resonance Imaging
(MRI) was obtained early postpartum (mean ± sd 48.9 ± 21.6 days) to identify LA
tear. Severity of LA muscle fiber loss was graded on an ordinal scale of: “0”
as no loss, “1” as <50% unilateral loss, “2” as ≥50% unilateral or <50%
bilateral loss, and “3” as ≥50% bilateral loss. Data were analyzed using
proportional odds modeling. Inclusion factors were explored as predictors of LA
tear severity and at analysis episiotomy, time spent actively pushing,
epidural, and oxytocin were also considered. The main outcome measures of
interest included grading of severity of LA muscle fiber loss on an ordinal
scale. Results: Respective counts/percentages of women within each 0 thru 3
ordered category of LA tear severity were: “0” = 58(64%), “1” = 9(10%), “2” =
15(17%), and “3” = 8(9%). Estimates and 95% CI for significant demographic or
obstetric univariate predictors of LA tear severity level were age, OR 1.093
(CI 1.012 - 1.180), p = 0.023; and time spent in active
pushing, OR 1.089 (CI 1.005 - 1.180), p = 0.038. The other factors considered
were not significant. There were too few women with forceps deliveries to
analyze. Conclusion: In our enriched sample of primiparous women, 26% showed a
significant LA tear. Maternal age and time spent actively pushing independently
predict LA tear severity.