The Burden of OASIS Increases along with Socioeconomic Position – Register-Based Analysis of 980,733 Births in Finland

Abstract

BackgroundObstetric anal sphincter injury (OASIS) has been identified as a major preventable risk factor for anal incontinence.ObjectiveAim was to measure national variation in incidence of OASIS by socioeconomic status (SES).MethodsA retrospective population based case-control study using the data derived from the Finnish Medical Birth Register for the years 1991–2010. A total population of singleton vaginal births was reviewed. We calculated unadjusted incidences of OASIS stratified by SES and vaginal parity, and adjusted risks for OASIS in each social class, after controlling for parity, birthweight, mode of delivery, maternal age and maternal smoking. SES was recorded into five categories based on mother’s occupation at time of birth; upper white-collar workers such as physicians, lower white-collar workers such as nurses, blue-collar workers such as cleaners, others such as students, and cases with missing information.ResultsSeven per thousand (6,404 of 980,733) singleton births were affected by OASIS. In nulliparae the incidence of OASIS was 18% higher (adjusted OR 1.18 95% CI 1.04−1.34) for upper white-collar workers and 12% higher (adjusted OR 1.12 95% CI 1.02−1.24) for lower white-collar workers compared with blue-collar workers. Among women in these higher SES groups, 40% of the excess OASIS risk was explained by age, non-smoking, birthweight and mode of delivery. Despite the large effect of SES on OASIS, inclusion of SES in multivariable models caused only small changes in estimated adjusted effects for other established risk factors.ConclusionsOASIS at the first vaginal delivery demonstrates a strong positive social gradient. Higher SES is associated with a number of risk factors for OASIS, including higher birthweight and non-smoking, but only 40% of the excess incidence is explained by these known risk factors. Further research should address other underlying causes including differences in lifestyle or environmental factors, and inequalities in healthcare provision.

Obstetric anal sphincter injuries—Maternal, fetal and sociodemographic risk factors: A retrospective register‐based study

“…Women with fewer than 9 years of education had a 15% lower risk of reported OASIS compared with those with more than 3 years of higher education after adjusting for maternal characteristics. Similar results are seen in a Finnish study where higher socioeconomic status was associated with an 18% increased risk of OASIS 23 . A British study showed that women of high socioeconomic status were more than twice as likely to experience OASIS compared with those of low socioeconomic status 24 .…”

“…Similar results are seen in a Finnish study where higher socioeconomic status was associated with an 18% increased risk of OASIS. 23 A British study showed that women of high socioeconomic status were more than twice as likely to experience OASIS compared with those of low socioeconomic status. 24 This difference is somewhat surprising and difficult to explain.…”

The MATEX cohort – a Finnish population register birth cohort to study health effects of prenatal exposures

“…Socioeconomic status is a strong indicator of health behaviour and dietary habits. Several studies showed that the risk for adverse pregnancy outcomes differs between socioeconomic groups in Finland [ 6 , 7 , 25 ].…”

“…Most commonly birth outcomes, such as birth weight, small for gestational age and preterm birth are used from the MBR. Other risk factors and health endpoints analysed with MBR data, include for example socioeconomic status [ 6 , 7 ], maternal age [ 8 , 9 ], reproductive history [ 10 ], stillbirth and neonatal mortality [ 11 , 12 ], and neurodevelopmental disorders [ 13 , 14 ]. The MBR data are not always used for identification of the study population or endpoints of interest, but also to identify confounding factors [ 15 ].…”

Management of 3rd and 4th Degree Perineal Tears after Vaginal Birth. German Guideline of the German Society of Gynecology and Obstetrics (AWMF Registry No. 015/079, October 2014)

“…" lateral episiotomy in vacuum extraction (OR 0.6) [17,18] " women with nicotine abuse have a lower risk for a higher degree perineal tear (OR 0.72 at the first birth) [20] The following obstetric measures are neither prophylactic nor do they increase the risk for higher degree perineal tears [8,11,[21][22][23][24][25]:…”