TUCSON, ARIZ. — One woman in four suffers neuropathic injury to the levator ani with her first delivery, according to a novel study that used pre- and postpartum concentric needle electromyographic examinations to study muscle function.
Cesarean sections performed during labor were not protective in the study conducted by Dr. Alison C. Weidner and her associates at Duke University Medical Center and presented at the annual meeting of the Society of Gynecologic Surgeons.
Initial EMG studies were performed on 58 primiparous women in the early third trimester, providing baseline data on muscle function at four separate sites of the levator ani. A quantitative amplitude analysis provided data on muscle function at rest and during moderate and maximum voluntary contractions.
Information was collected on the subjects' labor and delivery patterns, and follow-up examinations were performed 6 weeks and 6 months post partum.
The mean age of the subjects was 29 years, and their mean body mass index was 25 kg/m
Evidence of neuropathic injury was seen in 14 (24%) of 58 subjects at the 6-week examination and 17 (29%) of 58 at the 6-month examination, said Dr. Weidner, chief of the division of urogynecology at the Durham, N.C., institution.
Some women who demonstrated neuropathic injury at 6 weeks were normal by 6 months, while a few who seemed normal at 6 weeks showed evidence of injury at 6 months.
Dr. Weidner said patterns of muscle recruitment in women who exhibited injury only at 6 months suggest that muscle atrophy takes time, and that the full extent of damage was not clear at the 6-week visit.
“My point is that all of the patients who had this pattern were actually suffering levator injury at the time of delivery,” although it could not be measured initially, she explained.
A close look at obstetric variables revealed findings that Dr. Weidner called “striking.”
For example, the 11 women who underwent a C-section during labor suffered injury rates equivalent to those seen in the 36 women who had spontaneous vaginal deliveries and nearly as high as the 8 who had operative vaginal deliveries.
Only the three women who had elective C-sections seemed to be spared significant levels of injury, with just one woman showing injury at one of the four levator ani sites measured at 6 months post partum.
That C-section was not protective in the context of labor surprised Dr. Weidner, since only 2 of those 11 patients progressed far enough in labor to push.
Another interesting finding was the role of a prolonged second stage of labor in women who received epidural anesthesia, which has historically been assumed to lead to greater injury to the pelvic floor. In fact, a shorter duration of epidural analgesia during labor and operative vaginal delivery were independently associated with a higher rate of injury in a logistic regression analysis.
A formal discussant of Dr. Weidner's paper, Dr. Michael Aronson of the University of Massachusetts, Worcester, said the study constituted “a very important contribution to the literature” that may shed light on potentially modifiable mechanisms of injury during labor and delivery.