Influence of the duration of the second stage of labor on the likelihood of
obstetric anal sphincter injury
#MMPMID25439012
Aiken CE
; Aiken AR
; Prentice A
Birth
2015[Mar]; 42
(1
): 86-93
PMID25439012
show ga
BACKGROUND: Duration of the second stage of labor has been suggested as an
independent risk factor for clinically detectable obstetric anal sphincter injury
in low-risk nulliparous women. METHODS: A retrospective 5-year cohort study was
conducted in a UK obstetrics center which included a high-risk delivery unit and
a low-risk birthing center. The study included 4,831 nulliparous women with
vertex-presenting, single, live-born infants at term, stratified according to
spontaneous or instrumental delivery. Binary logistic regression models were used
to examine the association between duration of second stage and sphincter injury.
RESULTS: Three-hundred twenty-five of 4,831 women (6.7%) sustained sphincter
injuries. In spontaneously delivering women, no association between duration of
the second stage and the likelihood of sphincter injury was recorded. Factors
associated with increased likelihood of sphincter injury included older maternal
age, higher birthweight, and Southeast Asian ethnicity. In contrast, for women
undergoing instrumental delivery, a longer second stage was associated with an
increased sphincter injury risk of 6 percent per 15 minutes in the second stage
of labor before delivery. CONCLUSIONS: For spontaneous vaginal deliveries,
duration of the second stage of labor was not an independent risk factor for
obstetric anal sphincter injury. The association between prolonged second stage
and sphincter injury for instrumental deliveries is likely explained by the risk
posed by the use of the instruments themselves or by delay in initiating
instrumental assistance. Attempts to modify the duration of the second stage for
prevention of sphincter injuries are unlikely to be beneficial and may be
detrimental.
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