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BioMed Research International
Volume 2014 (2014), Article ID 395803, 8 pages
Research Article

Maternal Body Mass Index and Risk of Obstetric Anal Sphincter Injury

Department of Obstetrics and Gynaecology and Department of Clinical and Experimental Medicine, Linköping University, 581 85 Linköping, Sweden

Received 26 February 2014; Accepted 2 April 2014; Published 15 April 2014

Academic Editor: Sohinee Bhattacharya

Copyright © 2014 Marie Blomberg. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Objective. To estimate the association between maternal obesity and risk of three different degrees of severity of obstetric anal sphincter injury. Methods. The study population consisted of 436,482 primiparous women with singleton term vaginal cephalic births between 1998 and 2011 identified in the Swedish Medical Birth Registry. Women were grouped into six categories of BMI. BMI 18.5–24.9 was set as reference. Primary outcome was third-degree perineal laceration, partial or total, and fourth-degree perineal laceration. Adjustments were made for year of delivery, maternal age, fetal head position at delivery, infant birth weight and instrumental delivery. Results. The overall prevalence of third- or four-degree anal sphincter injury was 6.6% (partial anal sphincter injury 4.6%, total anal sphincter injury 1.2%, unclassified as either partial and total 0.2%, or fourth degree lacerations 0.6%). The risk for a partial, total, or a fourth-degree anal sphincter injury decreased with increasing maternal BMI most pronounced for total anal sphincter injury where the risk among morbidly obese women was half that of normal weight women, OR 0.47 95% CI 0.28–0.78. Conclusion. Obese women had a favourable outcome compared to normal weight women concerning serious pelvic floor damages at birth.