A magnetic transducer for the detection of the fetal engagement level in part-task trainers

Assessing the level of descent of the fetal head in the birth canal during a pelvic examination is a critical skill required by gynecologists and midwifes to avoid injuries for the mother and the newborn. A way to train this ability in a riskless environment is through medical simulation; however, the majority of tools do neither provide visual feedback of the location of the fetus inside the birth canal, nor give the possibility to quantitatively assess this skill. This work aimed at creating a low-cost transducer based on magnetic fields that discriminates between nine levels of descent of the fetal head, namely engagement levels, usable with part-tasks pelvic trainers. Starting with neodymium magnets, we designed a magnetic transducer so that each level was identified by a unique combination of magnetic fields. Three Hall effect sensors detect polarity and intensity of the field generated by 27 permanent magnets, organized in a $9\times 3$ matrix, and each level, corresponding to one row of the matrix, is uniquely encoded by the sensors. The system was theoretically analyzed in simulation, then tested using a customized prototype and finally integrated into an existing birth simulator. The transducer is wireless and avoids any obstruction in the birth canal, as it does not require any power supply to generate magnetic fields and the sensors are connected to the hardware in the fetal manikin. Also, its dimension and ease to install make it usable with many pelvic models, which can be turned into sensorized simulators providing visual feedback and quantitative evaluations.