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

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.

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.

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 (χ²(4)=17.825, p < 0.0005) and antepartum SP and postpartum EAS defects to be associated with SP reduction (χ²(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 (χ² (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.

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.