Background: Infant or maternal injury during vaginal delivery is a constant threat to all involved, but difficult to predict.
Objective: To estimate the risk of birth injuries in an institution favouring trial of vaginal birth when there was doubt of the best mode of delivery.
Design: A retrospective cohort study.
Setting: University Hospital.
Population: Singleton 14,359 vaginal deliveries in cephalic presentation during 5(1/2) years.
Methods: The total caesarean section rate during this period was 9%. The likelihood of injury was evaluated by logistic regression analysis with injury as the dependent variable and maternal height and child birthweight as explanatory variables in birth injury risk estimation.
Main outcome measures: Infant injury defined as one of the following: shoulder dystocia, clavicle fracture or brachial plexus injury; and maternal injury as anal sphincter rupture (ASR).
Results: There were a total of 318 infant injuries in 282 infants and 423 ASRs. A strong correlation was found between injury and both fetal macrosomia and short maternal stature, but macrosomia was a stronger indicator of injury. Birth injury risk estimation curves were constructed based on maternal height and birthweight.
Conclusions: The present results confirm a strong correlation between fetal macrosomia and short maternal stature and the likelihood of injury during vaginal birth. Risk estimation curves were constructed that might be of great value for the obstetrician in choosing the mode of delivery in these cases.