PURPOSE:A study was performed to evaluate the early morphologic and functional consequences of vaginal delivery on the anal sphincter in primiparous females.METHODS:Among a cohort of 197 primiparous females who agreed to participate in a clinical evaluation of fecal incontinence and in a transanal ultrasound examination 12 weeks after delivery, 52 also underwent anal manometry using a radial six‐port catheter, of whom 10 were asymptomatic and had a normal sphincter at ultrasound and the remaining 42 had clinical signs of anal incontinence or ultrasonographic defects of the anal sphincter or both. Anal sphincter pressures and asymmetry index were analyzed at rest and during voluntary squeeze. Manometric and ultrasound results were compared, together with clinical symptoms.RESULTS:Fourteen patients with clinical signs of anal incontinence had lower resting and squeeze anal pressures than continent patients (P<0.05), but similar anal asymmetry indexes. Patients with incontinence and an anal defect had the lowest resting and squeeze anal pressures (P<0.05). Forceps assistance to delivery was not associated with a higher frequency of anal sphincter lesions. Resting and squeeze anal pressures were lower in the forceps group (P<0.005), but anal asymmetry indexes were similar. Finally, manometric results were identical in the presence or absence of anal sphincter endosonographic defects.CONCLUSIONS:Anal sphincter defects are frequent after the first vaginal delivery, but are not always associated with functional or clinical abnormalities. Resting and squeeze anal pressures were significantly decreased in patients with incontinence and an anal defect and after forceps‐assisted deliveries. Anal asymmetry index was not found useful in this population of young primiparous females.