PROSPECTIVE COMPARISON OF THEINCIDENCE OF OASIS BETWEEN A WESTERN AND ASIAN HOSPITAL USING ASINGLE EXAMINER
L. J. BATES1, J.MELON 2, R. M. TURNER 3, S. CHAN 4,E. KARANTANIS 5;
1Department ofUrogynaecology, St George Hosp., Univ. of NSW, NSW, Australia,2Department of Obstetrics and Gynaecology, Prince of WalesHosp., The Chinese Univ. of Hong Kong, Statin, Hong Kong, Hong Kong,3School of Public Health and Community Medicine,, Univ. ofNew South Wales, NSW, Australia, 4Chinese Univ. of HongKong, Shatin, Hong Kong, 5Department of Urogynaecology, StGeorge Hosp., Univ. of New South Wales, NSW, Australia.
Introduction: Studies in Westerncountries show Asian women have a higher risk for OASIS (third andfourth degree perineal tears) (1), but in Asia, reported rates aremuch lower. Hong Kong has reported rates of 0.3-0.9% (2). Whether arectal examination, which increases detection rates, was performed aspart of the assessment was not reported. If OASIS rates for Asianwomen in Australia are higher than in Asia, aetiological factorsassociated with this difference need to be established.
Objective:The primary objective was to obtain an accurate comparison of OASISrates in Asian primiparous women in an Asian and Western location, byemploying the same experienced examiner at both sites tosystematically assess women immediately postpartum. A secondary aimwas to study birth factors that may have influenced the rates ofOASIS at both units.
Methods: A prospective observationalstudy of primiparous women of East and South East Asian descent >36weeks gestation, recruited from a University Hospital in Hong Kong,China, and a tertiary hospital in Sydney, Australia. Demographics(Age, booking body mass index (BMI), place of birth, gestational age,partners ethnicity and height) were recorded.
Birth variablesrecorded included perineal length, duration of first and second stageand active pushing, delivery technique, including hands-on perineum,instrumental delivery, use of epidural block (EDB), angle and lengthof the mediolateral episiotomy (MLE), and infant birthweight. At bothsites, once informed consent was obtained, the same independentinvestigator (who travelled to Hong Kong) attended the delivery andthen performed a systematic examination, including a rectalexamination to detect the presence or absence of OASIS as per theSultan Classification of perineal trauma.
Routinely collected dataof Asian women who did not consent or did not reach full dilatationwas collected from the birth register at each hospital to assess forbias.
To detect a difference in the proportion with an OASIS rateof 30% in Australia and 10% in Hong Kong, using a 5% significancelevel and 80% power, a sample size of 63 women was required at eachsite. Based on number of deliveries in Hong Kong (6500 per annum) itwas estimated that the independent investigator would travel to HongKong for two weeks. Recruitment in Sydney occurred over 10 months.Analysis was conducted in SPSS (version 23) and Stata SE14.2.
Results: In Australia 66 women, and 70 in Hong Kongwere recruited and attained a vaginal delivery. The baselinecharacteristics of the women did not differ at each site, or betweensites, for age, gestational age, or perineal length. There was nodifference in the Caesarean section rates.
OASIS rates of 34% inAustralia and 10% in Hong Kong (p=0.001) were significantly differentfrom each other and higher than previously reported, reflecting theuse of a rectal examination to increase detection. Infant birthweightwas 200g heavier in Australia (p=0.003), and in those that sustainedOASIS (P=0.05). Sydney had a higher instrumental rate, use of EDB,and longer duration of second stage and active pushing. Hong Kong hada higher episiotomy rate. Due to wide variation of deliverytechniques, comparison was difficult, therefore not included infurther analysis.
Multivariable analysis showed perineal length(OR=0.36, p=0.004) and birth weight (OR=1.14, p=0.039). As seen inFigure 1, in spontaneous deliveries, the risk of OASIS dramaticallyincreased once the length of perineum was less than 3cm andbirthweight increased. MLE in spontaneous births appeared protective,but was not significant (OR =0.59; p=0.521), though there was limitedpower.
Conclusions: By conducting astandardised rectal examination, the rate of OASIS in primiparousvaginal births in Asian women in an Eastern setting havesignificantly lower rates of OASIS than in a Western setting.Increased birthweight and short perineal length are independent riskfactors.
References: 1. Int Urogynecol J. 2015;26:1725-34.2. J Matern Fetal Neonatal Med. 2009;22(12):1116-21