OP, Vacuum Combo Raises Anal Sphincter Injury Risk


WHITE SULPHUR SPRINGS, W.VA. — Occiput posterior fetal head position during a vacuum delivery incrementally increases the risk of anal sphincter injury above the risk imposed by the vacuum alone, Jennifer Wu, M.D., said at the annual meeting of the South Atlantic Association of Obstetricians and Gynecologists.

In her retrospective study, vacuum delivery from the OP position was four times more likely to result in a sphincter-injuring third- or fourth-degree tear than vacuum delivery from the occiput anterior (OA) position.

“This is an important issue to consider when weighing the risks and benefits of performing a vacuum delivery from the OP position, especially when one of the goals is to reduce the risk of maternal perineal trauma,” said Dr. Wu of the University of North Carolina, Chapel Hill.

She retrospectively analyzed a total of 393 vacuum deliveries performed at the university from 1996 to 2003. Anal sphincter injury was defined as a third‐ or fourth-degree laceration.

There were 48 deliveries from the OP position and 345 deliveries from the OA position. Women in the OP group were significantly younger than those in the OA group (24 years vs. 28 years), more likely to be nulliparous (87% vs. 74%), and more likely to have received an episiotomy (35% vs. 14%).

The infants' gestational age, head circumference, and birth weight were not significantly different between the groups.

The overall anal sphincter injury rate was 24%. Significantly more women in the OP group sustained an anal sphincter injury (42% vs. 22%).

In a multivariate analysis that took into account fetal head position, body mass index, race, nulliparity, length of second stage, episiotomy, birth weight and head circumference, the OP position was four times more likely to be associated with an anal sphincter injury than the OA position.

In a previous retrospective study of 588 forceps deliveries, Dr. Wu also found an increased anal sphincter injury rate among OP deliveries, compared with OA deliveries (51% vs. 33%).

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