Objective To compare the effects of forceps delivery and spontaneous delivery on pelvic floor functions in nulliparous women.

Design A longitudinal prospective study with investigations during the first pregnancy, 10 weeks and 10 months after delivery.

Setting Antenatal clinic in a teaching hospital.

Population One hundred and seven patients aged 28.4 years, divided into those with forceps (n= 25) or spontaneous (n= 82) delivery.

Methods Investigations with a questionnaire, clinical examination, assessment of bladder neck behaviour, urethral sphincter function, intra-vaginal/intra-anal pressures during pelvic floor contractions.

Results The incidence of stress urinary incontinence was similar in both groups at 9 weeks (32%vs 21%, P= 0.3) and 10 months (20%vs 15%, P= 0.6) after delivery, as was the incidence of faecal incontinence (9 weeks: 8%vs 4%, P= 0.9; 10 months: 4%vs 5%, P= 1) and the decreased sexual response at 10 months (12%vs 18%, P= 0.6). Bladder neck behaviour, urethral sphincter function and intra-vaginal and intra-anal pressures were also similar in the two groups. However, 10 months after delivery, the incidence of a weak pelvic floor (20%vs 6%, P= 0.05) and the decrease in intra-anal pressure between the pre- and post-delivery values (−17±28 cm H2O vs 3±31 cm H2O, P= 0.04) were significantly greater in the forceps-delivered women.

Conclusions Forceps delivery is not responsible for a higher incidence of pelvic floor complaints or greater changes in bladder neck behaviour or urethral sphincter functions. However, patients with forceps delivery have a significantly greater decrease in intra-anal pressure and a greater incidence of a weak pelvic floor.