Changing incidence of anal sphincter tears in four Nordic countries through the last decades

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Abstract

Objectives

Anal sphincter rupture is a serious complication of a vaginal delivery. A considerable number of women suffer permanent anal incontinence after this type of injury. The incidence of sphincter tears is believed to have increased over several decades in Denmark, Norway, Sweden and Finland, but there seem to be significant differences in the incidence rates among these countries. The aim of this study is to compare frequency of anal sphincter tears among the four Nordic countries, and to discuss the possible reasons for the development.

Study design

Ecological register study. Anal sphincter ruptures are registered as third and fourth degree perineal tears in the national birth and hospital registries in the Nordic countries. Data from these registries were sampled from Denmark, Finland, Norway and Sweden. The incidences of anal sphincter ruptures were calculated as percentages of all vaginal deliveries and caesarean sections were excluded. The test of relative proportions, Chi-square and linear regression modelling were used to study the difference between countries and time trends.

Results

The frequency of anal sphincter rupture was significantly higher in three countries, Denmark 3.6%, Norway 4.1% and Sweden 4.2%, compared to Finland 0.6%. The trend was clearly increasing from the early 1970s in all countries.

Conclusions

There is a significant difference in the Nordic countries in the incidence of anal sphincter tears and a significant increment in the incidence over three decades. Our hypothesis is that change in the routines during labour may be one reason for this increment. Higher episiotomy frequency in Finland may be one contributing reason. We assume that there has been a change in the conduct of labour during the last decades, and protecting the perineum may have lost its importance in the three Nordic countries, while the classic method of protecting perineum is still in use in Finland.

Introduction

Anal sphincter rupture (ASR) is a serious complication of vaginal delivery and leads to anal incontinence in 40–59% of cases [1], [2], [3]. Primiparity, macrosomia and instrumental vaginal delivery seem to be the most important risk factors. Median episiotomy increases the risk of anal sphincter tear but several reports show that mediolateral episiotomy might reduce the risk [4], [5], [6]. Statistical data show increasing incidences of anal sphincter rupture in the Nordic countries over the last decades but the reasons are unknown. Both newborn babies and mothers are heavier than before, mothers are older and epidural analgesia has become more usual, but at the same time the caesarean section rate has increased. Accoucheurs failing to provide perineal protection has been discussed as a potential reason [7]. The aim of this study is to describe the changes in four Nordic countries and discuss the reasons for the development.

Section snippets

Materials and methods

Data from the national birth and hospital registries were sampled from Finland (Hospital Discharge Register 1987–2007 and Medical Birth Register 2004–2007 (THL)), Norway (Medical Birth Register, National Public Health Institute), Sweden (Medical Birth Register, National Board of Health and Welfare) and Denmark (Medical Birth Register, National Board of Health). The validity of data is quality assured by validity declarations in each medical birth registry and also in several studies [5], [7],

Results

Fig. 1 describes the development of the prevalence of anal sphincter tears in the Nordic countries. A statistically significantly increasing trend was observed in all countries (p < 0.001) until year 2004. The results were alike using all three analyzing methods. In Norway, Sweden and Denmark the rate of anal sphincter tears has been significantly higher than in Finland during the observed period (p < 0.001).

The Danish incidence was not available in the birth register before 1997, but Moller Bek et

Discussion

The medical birth registries in Denmark, Finland and Sweden have a validity declaration that presents their control system. Several clinical trials and methodogical studies have been conducted and published to validate the data in these registries [5], [7], [8], [10], [11], and data coming from registries have been shown to be reliable.

The incidence of ASR has increased significantly in Finland, Denmark, Norway and Sweden from the middle of 1990s, but the frequency in Denmark, Norway and Sweden

Conclusion

There is a significant difference among the Nordic countries in the incidence of anal sphincter tears and a significant increment in the incidence over three decades. The most important risk factors, primiparity, macrosomia and frequency of instrumental delivery, are similar in all the investigated countries. Perineal protection and delivery technique are very little discussed as a reason for the increment of ASR in the publications that we found. Changed attitudes to protecting the perineum

Acknowledgements

We highly appreciate the work of the four Nordic Medical Birth Registries gathering the data. Without this the present article would have been impossible to write.

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