4.3. The incidence of obstetric anal sphincter ruptures during childbirth has increased

Public examination of a doctoral dissertation in the field of nursing science

Doctoral candidate: MHS Sari Räisänen

Time and venue 4.3.2011 at 12 noon, Medistudia ML3, Kuopio Campus

Obstetric anal sphincter rupture (OASR) is a well-known complication of vaginal delivery; it can have serious implications for women’s health since it results in anal incontinence in 20-60% of those affected. The incidence of OASR varies widely; in 2008 it was reported at a level of 0.9% in Finland but 2.6-5.6% in the other Nordic countries. The purpose of this study was to identify the risk factors for OASR, and to describe trends in the incidence of OASR and episiotomy between 1997 and 2007 in Finland. A population-based inventory of 514,741 women with singleton vaginal deliveries, including all presentations and assisted deliveries, recorded in the Finnish Medical Birth Register was analyzed. For the years 1997-2003, the information on OASR was taken from the Hospital Discharge Register (HDR). Primiparous (=first vaginal delivery) (n=2,315) and multiparous (n=534) women with OASR were compared in terms of possible risk factors to primiparous (n=215,463) and multiparous (n=296,429) women without OASR, respectively, using stepwise logistic regression analysis.

The risk factors for OASR included forceps delivery, a prolonged active second stage of birth, delivery of an infant weighing more than 4,000 grams, and vacuum assistance. Lateral episiotomy was associated with a 17% lower risk of OASR among primiparous women in spontaneous vaginal deliveries; however this approach was inefficient since more than 900 primiparous women must be exposed to an episiotomy to prevent a single OASR. In vacuum assisted deliveries among primiparous women the equivalent number was 66, which is clinically more acceptable. Correspondingly, among the multiparous women, episiotomy was associated with a doubling of the risk of OASR. Furthermore, pain management was associated with 13-52% lower risk of OASR among both groups of women except epidural analgesia among the multiparous women that increased the risk 1.5-fold.

In Finland, the incidence of OASR has increased, from 0.2% in 1997 to 0.9% in 2007. The likelihood of OASR increased 3.28-fold among primiparous and 2.83-fold among multiparous women during the study period, 1997–2007. Changes in population characteristics and in the use of interventions were small, and consequently did not cause the increased OASR rate. The only exception was vacuum assisted deliveries, which explained about 9% of the rising OASR risk, in line with the increased use of this technique. The results of this study suggest that time factors were of minor importance to the increasing rate of OASR, because the risk of it was shown to be 11% lower during the night than daytime and 15% lower in July (the most popular holiday month) than other months. In fact, ca. 3- to 8-fold inter-hospital differences in OASR risks in primiparous and multiparous women, respectively, were of greater importance. Hospitals with high rates of OASR for primiparous women also had high rates for multiparous women, implying that treatment differences might have played a crucial role in the variations or that there were differences in registration routines or in diagnosing OASR.

The results suggest that episiotomy provided protection from OASR in the first vaginal birth, but was a risk factor in multiparous women. Among the multiparous women, episiotomy was performed prophylactically more often in those who were at a high risk of OASR than in low risk women, consequently there might have been confounding by indication. The results indicate the value of selective use of lateral episiotomy, and its routine use might be advisable in vacuum assisted deliveries for primiparous women. Inter-hospital differences suggest that, between the hospitals, there may be an important healthcare quality issue or differences in recording or diagnosing OASR.

The doctoral dissertation of Master of Health Sciences Sari Räisänen, entitled Obstetric Anal Sphincter Ruptures – Risk Factors, Trends and Differences Between Hospitals will be examinedat the Faculty of Health Sciences. The opponent in the public examination will be Docent Tytti Raudaskoski of Oulu University Hospital, and the custos will be Professor Katri Vehviläinen-Julkunen of the University of Eastern Finland.

Photo available for download at http://www.uef.fi/uef/vaitoskuvat

Contact: Sari Räisänen, p. 050 3378 258, shraisan@student.uef.fi

Publishing year: 2011

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