Abstract
PurposeThe present study aimed to assess the risk of obstetric anal sphincter injuries (OASIS) of a subsequent delivery after the previous OASIS in countries with low (Finland) and high rates (Norway and Sweden) of OASIS.MethodsThis population-based case–control study included women who experienced OASIS 1997–2002. 26,598 women with OASIS were included from countries with low (Finland) and high (Norway and Sweden) OASIS incidences. Each case was matched with one background-adjusted control without OASIS. A follow-up data, including all subsequent deliveries between 1998 and 2011 were then collected. Statistics significances were calculated using chi-square test, test for relative proportions and Students t test, where appropriate.ResultsOASIS in the first birth was associated with increased recurrences in subsequent births, 6.9% vs. 1.7% in Norway (p < 0.001); 4.5% vs. 0.7 (p < 0.001) in Sweden; and 2.1% vs. 0.8% in Finland (p = 0.038). In Norway, more than two deliveries occurred in 4.8% of cases and 6.2% of controls (p = 0.001), 4.2% vs. 5.1% in Sweden (p < 0.001), and 5.7% vs. 6.3% in Finland (p = 0.572). For women with OASIS in a previous delivery, the rates of cesarean deliveries in subsequent pregnancies were 16.4% (7.9% for controls) in Norway, and 16.3% (6.0% for controls) in Sweden, and 50.2% (14.2% for controls) in Finland. In all countries, the differences between cases and controls were significant (p < 0.001).ConclusionNext deliveries after OASIS are associated with increased frequency of new OASIS, more cesarean deliveries, and less subsequent deliveries in the high-risk population than women without previous OASIS.
Highlights
A common outcome of vaginal delivery is perineal trauma
We have shown that there is a threefold increase of repeated obstetric anal sphincter injuries (OASIS) in the low-risk, and four- to sixfold increases in the high-risk population
This means that 2.1% in the low-risk and 4.5–6.6% in the high-risk population will suffer from OASIS after a sphincter injury during their first delivery
Summary
The most serious among these injuries are third- and fourthdegree lacerations or obstetric anal sphincter injuries (OASIS). Mechanical damage of the anal sphincter muscles is assumed to be the most important risk factor for anal incontinence and anorectal symptoms in otherwise healthy. A better understanding of risks is necessary when counseling women with a prior OASIS. The risk of recurrence is a major factor in planning the mode of a subsequent birth. Women with prior OASIS were reported to be more likely to have a cesarean delivery for their birth [9, 10]. The OASIS rate in Finland has been significantly lower than in other Scandinavian countries, e.g., 1% in Finland compared to 4% in Sweden and Norway [11]
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