Effect of vaginal delivery on anal sphincter function in Asian primigravida: a prospective study.

INTRODUCTION AND HYPOTHESIS: The true incidence of obstetric anal sphincter injuries (OASI) among Asian primigravida is not known. This study aimed to evaluate OASI in Sri Lankan primigravida.

METHODS: One hundred and one consecutive primigravida in their last trimester were recruited from antenatal clinics at a tertiary care centre in Sri Lanka and followed up 6 weeks and 6 months after delivery. They were assessed using anorectal manometry (3D-ARM) and endoanal ultrasound (3D-EAUS) on both occasions.

RESULTS: Seventy-three (75.3 %) had vaginal delivery without instrumentation, whereas 3 (3.1 %) each delivered using forceps or vacuum. Twelve (12.4 %) had emergency caesarean sections and 6 (6.2 %) had elective caesarean sections. None had clinically identified anal sphincter injuries. EAUS identified IAS defects in 3 (5.1 %) and EAS defects in 28 (47.5 %). Both resting (p = 0.3) and squeeze (p = 0.001) pressures had decreased following childbirth. Multivariate analysis identified antepartum RP and postpartum EAS defects to be associated with RP reduction (χ(2)(4)=17.825, p < 0.0005) and antepartum SP and postpartum EAS defects to be associated with SP reduction (χ(2)(5)=31.517, p < 0.0005). Episiotomy was protective, whereas delivering after 40 weeks' gestation and delivering a baby with a longer length increased the risk of SP reduction. EAS defects (χ(2) (6)=23.502, p = .001) were more common in mothers who had labour augmented by oxytocin and in those who delivered a baby with a larger head circumference. Labour induction and delivering a longer baby were protective for EAS defects.

CONCLUSIONS: Several risk and protective factors for the structural and functional damage of sphincters were identified. These findings will help to formulate a policy to minimize future obstetric anal sphincter injuries.