Risk factors for obstetric anal sphincter injuries in twin deliveries: a retrospective review.

Abstract

Risk factors for obstetric anal sphincter injuries (OASIS) have been well-established in singleton pregnancies. Considering the unique characteristics of twin deliveries, our aim was to identify risk factors for OASIS that are specific to twins. A retrospective study of all vaginal twin deliveries in a tertiary center between 2000 and 2014. Women who experienced OASIS (the OASIS group) were compared with those whose anal sphincter was intact (controls). Overall 717 women were eligible for the study, of whom 20 (2.8%) experienced OASIS. Women in the OASIS group were more likely to be nulliparous (95.0% vs 53.7%, p < 0.001) and were characterized by a higher gestational age at delivery (36.1 ± 2.5 vs 34.6 ± 3.3, p = 0.04), a higher birth weight for both twin A and twin B (2,507 ± 540g vs 2,254 ± 525g, p = 0.03, and 25,49 ± 420g vs 2,232 ± 606g, p = 0.004 respectively), and a higher rate of episiotomy (40.0% vs 14.2%, p = 0.001), instrumental delivery for twin A (80.0% vs 13.5%, p < 0.001) or twin B (80.0% vs 18.7%, p < 0.001), and inter-twin delivery interval of over 30min (20.0% vs 7.5%, p = 0.04). The only factor that remained significant on multivariate analysis was instrumental delivery: forceps delivery of twin A (OR = 8.8, 95% CI 2.6-30.1), vacuum extraction of twin A (OR = 9.2, 95% CI 2.6-34.6), and forceps delivery of twin B (OR = 15.4, 95% CI 4.9-48.6). In women with certain combinations of risk factors the risk of OASIS was as high as 30%. The overall rate of OASIS in twins is low and instrumental delivery, especially by forceps, is a risk factor.