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The use of forceps during delivery is associated with muscle damage that can lead to later pelvic organ prolapse, Australian researchers found.

In a prospective cohort study, use of forceps was associated with nearly four times the risk of avulsion of the levator ani muscles, according to K.L. (Clara) Shek, MD, and Hans Peter Dietz, MD, both of the University of Sydney's Nepean Clinical School.

On the other hand, epidurals appeared to reduce the risk of related but lesser damage to the levator muscles, they reported online in the British Journal of Obstetrics and Gynaecology.

Levator avulsion has been seen in up to 30% of women who deliver vaginally and is a strong risk factor for pelvic organ prolapse, the researchers noted. But even without full-blown avulsion, traumatic overdistension -- or microtrauma -- may be another form of levator injury that leads to prolapse, Shek and Dietz argued.

To try to pin down risk factors, they analyzed data from a prospective cohort of 488 women undergoing their first pregnancy and aiming for a vaginal delivery. All the women had a prepartum interview and a four-dimensional translabial ultrasound examination. They were invited to return for another ultrasound between three and four months after delivery.

A total of 367 women (75%) returned for the postpartum assessment, including 187 (51%) after normal vaginal delivery, 34 (9%) after vacuum delivery, 20 (5%) after a forceps delivery, and 126 (34%) after a cesarean section.

The researchers diagnosed levator avulsion in 32 (13%) of the women who delivered vaginally and in none of those who had a cesarean section.

A multivariate regression analysis showed that forceps delivery was associated with an increased risk of avulsion, with an odds ratio of 3.83 and a 95% confidence interval from 1.34 to 10.94, which was significant at P=0.01.

Traumatic overdistension was defined as more than a 20% peripartum increase in hiatal area on Valsalva maneuver. By that definition, the researchers reported, 28.5% of the women had suffered irreversible overdistension.

The risk was positively associated with the length of second stage of delivery, with an odds ratio of 1.01 per minute (95% CI 1.0 to 1.02, P=0.001).

On the other hand, intrapartum epidural appeared to have a protective effect, with an odds ratio of 0.42 (95% CI 0.19 to 0.93, P=0.03).

The findings should not, however, rule out the use of forceps, according to the journal's editor-in-chief, Philip Steer, MD.

"There will be occasions when the use of forceps to help deliver the baby is appropriate," Steer said in a prepared statement. But the study shows forceps deliveries have some risks "so it is important to ensure that all our trainees receive good training in carrying these out and existing doctors keep up-to-date with their skills."

On the other hand, he noted, it is "reassuring" that epidurals can play a protective role. "The short-term priority is to reduce pain during childbirth but the longer term effect of reducing muscle damage and prolapse is welcome."

Shek and Dietz noted that the study strengths include its prospective design and the large population. On the other hand, the follow-up rate was only 75%, they noted, and the timing of follow-up also varied widely.

Nor was the Valsalva maneuver standardized, which might affect the assessment of hiatal area on Valsalva maneuver.

The researchers also noted that the results are specific to the largely Caucasian and younger than average local population, as well as to local obstetric practices.