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. 2010 Jul;116(1):25-34.
doi: 10.1097/AOG.0b013e3181e2f50b.

Trends in risk factors for obstetric anal sphincter injuries in Norway

Elham Baghestan  1 , Lorentz M Irgens, Per E Børdahl, Svein Rasmussen
Affiliations

Trends in risk factors for obstetric anal sphincter injuries in Norway

Elham Baghestan et al. Obstet Gynecol. 2010 Jul.

Abstract

Objective: To investigate risk factors for obstetric anal sphincter injuries in a large population-based data set, and to assess to what extent changes in these risk factors could account for trends in obstetric anal sphincter injuries.

Methods: This is a population-based cohort study on data from the Medical Birth Registry of Norway between 1967 and 2004, including all vaginal singleton deliveries of vertex-presenting fetuses weighing 500 g or more. Women with their first birth before 1967 and births with previous obstetric anal sphincter injuries were excluded, leaving 1,673,442 births for study. The outcome variable was third- and fourth-degree obstetric anal sphincter injuries. The associations of obstetric anal sphincter injuries with possible risk factors were estimated by odds ratios (ORs) obtained by logistic regression.

Results: The occurrence of obstetric anal sphincter injuries increased from 0.5% in 1967 to 4.1% in 2004. After adjusting for demographic and other risk factors, as well as possible confounders, the increase of obstetric anal sphincter injuries persisted, although reduced (unadjusted OR 7.1; 95% confidence interval [CI] 6.8-7.4; adjusted OR 5.6; 95% CI 5.3-5.9). Obstetric anal sphincter injuries were significantly associated with maternal age 30 years or older, vaginal birth order of one, previous cesarean delivery, instrumental delivery, episiotomy, type 1 diabetes, gestational diabetes, induction of labor by prostaglandin, size of maternity unit, birth weight 3,500 g or more, head circumference 35 cm or more, and African or Asian country of birth.

Conclusion: Risk of obstetric anal sphincter injuries considerably increased in Norway in 1967 to 2004. Changes in the risk factors studied could only partially explain this increase.

Level of evidence: II.

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References

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