A device to adjust a strip of circular adjustment around the cephalic pole, that is inserted within the delivery channel together with a sleeve and an applicator, where the sleeve is a flexible sleeve, which has both ends open, with a fold in its middle part where it is fixed, on the inner side of the fold, and where the sleeve is provided with at least two traction handles on the ends of the inner fold, and where the applicator is provided with a butt head, spatulas that fit in the pockets of the sleeve and a guide to indicate the movement of the spatulas with respect to the head butt, and comprises: a strip of circular adjustment of flexible material and at least an adjustment axis with its respective driving mechanism. The method of usage of the device comprises the steps of: a) inserting the device-sleeve-applicator set within the delivery channel uptil the guide shows the middle of the movement of the spatulas b) making a first adjustment of the strip of circular adjustment rotating at least one adjustment axis c) reading on the indicator of the rotation angle the diameter of the head of the fetus d) continuing to insert the device-sleeve-applicator set until its final position e) continuing with a final adjustment of the strip of circular adjustment of at least half turn f) removing the applicator and g) pulling from the sleeves handles to extract the fetus.Un dispositivo para ajustar una tira de ajuste circular alrededor del polo cefálico, que se introduce dentro del canal de parto en conjunto con una manga y un aplicador, donde la manga es una manga flexible, que tiene ambos extremos abiertos, con un pliegue en su parte media donde se la fija, del lado interno del pliego, y estando la manga provista de al menos dos asas de tracción en los extremos del pliegue interior, y donde el aplicador está provisto de un tope de cabeza, espátulas que calzan en los bolsillos de la manga y una guía indicadora del desplazamiento de las espátulas respecto del tope de cabeza
