High birth weight is the main risk factor for birth injuries to the anal sphincter muscles of the person giving birth, according to a study at the University of Gothenburg. This new method for predicting the risks could improve care and reduce injuries.
Five percent of women giving birth to their first child in Sweden sustain birth injuries in the form of obstetric anal sphincter injuries (OASI), affecting the muscles responsible for controlling gas and bowel movements. These injuries can lead to long-term problems and impact physical health as well as quality of life.
The aim of this study, published in the Journal of Clinical Epidemiologywas to develop and validate a prediction model that provides an assessment of the risk of OASI in advance of a vaginal delivery.
The study is based on registry data from all 45 maternity units in Sweden for the period 2009 to 2017. In total, some 600,000 singleton, head-first births, the most common form of delivery, were examined.
Larger babies increased the risk the most
Prediction models were devised for three common delivery scenarios: first vaginal delivery, vaginal birth after cesarean section, and second vaginal delivery. A wide range of risk factors were included, such as the baby’s birth weight, assisted birth with, for example, a vacuum cup, the height and age of the person giving birth, and previous OASI.
The baby’s birth weight was found to be the strongest predictor of OASI in all delivery scenarios — larger babies increased the risk of severe vaginal tears. Among those giving birth to their second child vaginally, previous OASI was a strong indicator of a repeat injury. A third risk factor was the use of a vacuum cup.
The prediction model for those giving birth vaginally for the second time was most accurate, followed by the models for first-time vaginal birth and vaginal birth after cesarean section. However, the reliability of all three models was on a par with similar and established prediction tools used in other fields, such as cardiovascular disease and breast cancer.
Basis for joint decisions
The study’s lead author is Jennie Larsudd-Kåverud, doctoral student in obstetrics and gynecology at the University of Gothenburg and obstetrician at Sahlgrenska University Hospital:
“The statistical models used in this study enabled us to distinguish at-risk individuals on the same level as other prediction models currently widely used in healthcare,” she notes.
Until now, there has been no tool in clinical use that predicts the risk of OASI during childbirth in the way that this newly developed calculator does. The aim is to reduce the number of injuries by implementing the right measures at the right time.
“The models that have been developed provide both healthcare professionals and pregnant women with a tool for assessing the risk of severe birth injury. If the risk is low, concerns can be mitigated. If the risk is higher, it provides opportunity for more careful joint planning and prevention,” Jennie Larsudd-Kåverud ends.