Objective To establish the effect of childbirth on pudendal nerve function and identify obstetric factors associated with such damage.
Design A prospective investigational study.
Setting Antenatal clinic, St Bartholomew's (Homerton) Hospital.
Subjects One hundred and twenty-eight unselected pregnant women beyond 34 weeks’ gestation.
Intervention Pudendal nerve terminal motor latencies (PNTML) and perineal plane were measured during pregnancy and six to eight weeks after delivery, and remeasured in a subgroup (n= 22) at six months.
Main outcome measures Effect of mode of delivery on PNTML and the plane of the perineum.
Results Vaginal delivery resulted in a significant (P < 0.0001) prolongation of the mean PNTML bilaterally in both primipara (n= 57) 1.91 ms (SD 0.19) vs 2.00 ms (SD 0.22), antenatal vs postnatal, right PNTML; 1.96 ms (SD 0.21) vs 2.06 ms (SD 0.24) left PNTML, and multipara (n= 32) (P < 0.01). Perineal descent during straining was also increased after vaginal delivery (P < 0.001). Greater damage to the pudendal nerve occurred on the left side (P= 0.03). PNTML were not altered after elective caesarean section (n= 7), but were increased on the left side when caesarean section was performed during labour (1.94 ms (SD 0.13) vs 2.08 ms (SD 0.29), P < 0.01). A heavier baby and a longer active second stage of labour were both associated with significant prolongation of PNTML. Eight out of 12 women with a prolonged PNTML at six weeks had normal measurements when restudied six months after delivery.
Conclusion Vaginal delivery, particularly the first, results in significant pelvic floor tissue stretching and pudendal nerve damage. Women who have a caesarean section during labour may also be at risk of pudendal nerve damage. The process of labour and vaginal delivery can both cause pudendal nerve damage which may be asymmetrical in extent.