Validating the MFMU TOLAC Calculator in a Canadian Obstetric Population

The rate of cesarean deliveries in Canada has been increasing. One risk factor for cesarean delivery is having a previous cesarean delivery. For patients who have had a previous cesarean delivery, a trial of labour after a previous cesarean delivery (TOLAC) is an option for appropriate candidates. In the Society of Obstetricians and Gynecologists guideline for TOLAC, the maternal-fetal medicine units (MFMU) vaginal birth after cesarean (VBAC) calculator is referenced as a tool to counsel patients.

This study examines whether the MFMU tool is predictive of outcomes in an obstetric population in a tertiary care centre and how to modify the tool to make it more applicable to obstetric patients at our centre.

We analyzed 494 medical records involving patients who underwent TOLAC in a tertiary care centre from 2016 to 2021.

We demonstrated that the MFMU tool is a fair predictor of the mode of delivery for obstetric patients in a tertiary care centre (area under the curve = 0.79; 95% CI 0.75-0.83, P < 0.001). The MFMU tool became a good predictor of VBAC by removing chronic hypertension (area under the curve = 0.81; 95% CI 0.77-0.85, P < 0.001). BMI was associated with the success of VBAC for persons with heights of 164-170 cm (P = 0.002). Persons with heights over 170 cm were 3 times more likely to have a VBAC than persons with heights less than 164 cm (OR 3.07; 95% CI 1.76-5.37, P < 0.001).

To the best of our knowledge, this is the first study examining the validity of the MFMU tool in a Canadian population.