Plain English Summary
Background and study aims
After childbirth many women have a tear to the skin between the vagina and anus. When these tears also involve the underlying muscles controlling the anus they are referred to as OASIS (Obstetric Anal Sphincter Injury). OASIS is the most common cause of anal incontinence (gas, liquid or solid stool leakage) in women and often leads to great physical and social suffering and there is very little these patients can be offered. Evidence shows that by repairing these injuries directly and properly, later problems with anal incontinence can be reduced. Unfortunately, many injuries are missed at the obstetric ward, since the only examination following childbirth is an inspection of the vagina and perineum and a digital anal examination. Because of the bleeding and swelling, damage to the muscles is hard to recognise. In this study, the three-dimensional ultrasound (3-D EAS) will be used to investigate how many OASIS that are actually missed with the clinical routine of today. 3-D EAS is the gold standard for evaluating the anal sphincter muscles. It is routinely used in departments specialising in pelvic floor disorders but not in obstetric care.
Who can participate?
Women giving birth for the first time at Östersunds Hospital.
What does the study involve?
After a participant has given birth, the midwife does the routine clinical examination and fill in the findings in a study protocol. She or he then performs the 3-D EAS recording. The recording only takes about a minute and is not painful. Each participant then comes back to the hospital 12 weeks after delivery for a new 3-D EAS examination to make sure no injuries are missed due to bleeding and swelling. The recordings are analysed by specialists and a comparison made between the clinical findings and the 3-D EAS findings to see how many OASIS are actually missed with today’s routines.
What are the possible benefits and risks of participating?
Taking part in the study is voluntary and a written consent will be obtained from all women. There are no risks with taking part and if we find large injuries on the recording we will break the code and contact the obstetricians. This will benefit the women taking part in the study.
Where is the study run from?
Östersunds Hospital (Sweden)
When is the study starting and how long is it expected to run for?
February 2015 to September 2017
Who is funding the study?
Östersund Hospital (Sweden)
Who is the main contact?
Dr Pär Nordin
Missed obstetric anal sphincter injury following vaginal delivery in primiparous women: a single center interventional study
The hypothesis is that the number of missed or undiagnosed obstetric anal sphincter injuries (OASIS) is high with the clinical examination routine of today.
Regional ethics committee, Umeå (Regionala etikprövningsnämnden i Umeå), 17/08/2015, ref: 2015-183-31M
A single center interventional study
Primary study design
Secondary study design
Non randomised study
Patient information sheet
Not available in web format, please use contact details to request a participant information sheet
Obstetric anal sphincter injury (OASIS)
The 3-D EAS (3-D imaging of the external anal sphincter) will be performed using a Flex Focus 500 Ultrasound scanner (BK Medical, Denmark) with a 8838 axial endoscopic probe. All the midwives will receive information and training in how to perform the recording. The scanner will be pre-set and ready in the delivery ward. All the 3-D data will be stored and then reviewed by two-three independent examiners, all doctors specially trained in ultrasound and using the same 3-D viewing software (BK Medical).
Data collection and follow up
Prior to the delivery at their antenatal visit, about gestation week 18, data concerning the patient will be collected including age, ASA, medicines, body mass index and co-morbidity. Together with the written consent they will also fill in a short form with questions about earlier surgery and/or problems with the anal sphincter and a validated wexner incontinence score form. The problem with discharge and other pregnancy-related events that could possibly affect the wexner score will at this time of the pregnancy probably not yet have arisen. The patients included in the study will after the delivery be examined by the mid-wife in charge who will inspect the vagina and make a digital anal examination. She or he will then fill in a prefabricated study protocol classifying the degree of the tear according to the WHO- classification (see definitions below) and then perform the blinded 3-D EAS-recording following step-by-step instructions. This will take place while the woman is still in supine position with legs in stirrups. The recordings will then be analysed by two independent and specially trained doctors using a specialised protocol including the Nordeval score and Stark score. After 12 weeks, a new 3D-EAS recording will be made to make sure no sphincter tears are missed because of oedema or bleeding, which may be present immediately post partum and make the image more difficult to analyse. A comparison will then be made of the number of OASIS found by clinical digital examination and the number identified with the 3-D EAS. Facts about the pregnancy, delivery and the new born will also be collected, including gestation week at delivery, type of anaesthesia, the use of instruments and/or episiotomy, induction of labour, augmentation of labour, weight and head-size of the infant, fetal presentation and APGAR score.
Tears of the perineal area that occur at childbirth are usually classified into four degrees. A first-degree tear is defined as a laceration involving the perineal skin and vaginal mucous membrane but not the underlying fascia and muscle. A second-degree tear involves the fascia and muscles of the perineal body, but not the anal sphincter. A third-degree tear involves the anal sphincter/sphincters. A fourth-degree also involves the anal or rectal mucosa.
Third and fourth degree tears can also be referred to as OASIS.
Primary outcome measures
To compare the clinical examination with inspection and digital anal palpation to 3-D EAS, to examine the number of OASIS missed at clinical post-partum examination. Shortly after delivery the patients will be examined by the midwife or in eligible cases a doctor who will inspect the vagina and make a digital anal examination. Their findings will be documented in a study protocol classifying the degree of the tear according to the WHO- classification. The anal ultrasound will then be performed by an independent midwife clueless to the findings in the digital examination. The EAS finding will be saved in a data base for revision and classification within 2 weeks. Ultrasound findings will be classified using the Starck scoring system for sphincter defects. After 12 weeks, a new 3D-EAS recording will be made by a mid-wife to make sure no sphincter tears are missed because of oedema or bleeding, which may be present immediately post partum and make the image more difficult to analyse.
Secondary outcome measures
To examine risk factors for OASIS. Facts about the pregnancy, delivery and the new born will be collected, including gestation week at delivery, type of anaesthesia, delivery position, the use of instruments and/or episiotomy, induction of labour, augmentation of labour, weight and head-size of the infant, fetal presentation and APGAR score.
Overall trial start date
Overall trial end date
Participant inclusion criteria
All primiparous women who deliver vaginally at Östersunds hospital during the study-period
Target number of participants
Participant exclusion criteria
1. Prior history of faecal incontinence
2. Anal sphincter surgery
3. Other known sphincter insufficiency
Recruitment start date
Recruitment end date
Countries of recruitment
Trial participating centre
Department of Surgery
Funding Body Type
Funding Body Subtype
Results and Publications
Publication and dissemination plan
Intention to publish date
Participant level data
To be made available at a later date
Results - basic reporting