A diameter regulator device to extract a fetus from a cavity, comprising:, flexible sleeve folded in its central area thus defining an inner sleeve and an external sleeve, and thus having a distal end and a proximal end, wherein the proximal end has at least two traction handles (10,11), the proximal ends of the inner sleeve and the external sleeve linked among each other, wherein the distal end and the proximal end are both open, and presenting in the distal end the fold which defines the inner sleeve and the external sleeve, and wherein the external sleeve has longitudinal pockets all along and its inner part to lodge the spatulas of the applicator, an applicator comprising a cup, spatulas that fit in the longitudinal pockets of the external sleeve and a guide indicator of the movement of the spatulas with respect to the cup, CHARACTERIZED in that: the diameter regulator device further comprises an adjustment strip having ends being made of a flexible material, and being formed into an open circumferential shape with a longitudinal opening between the ends, wherein the adjustment strip is placed between the inner sleeve and the external sleeve thereby encircling the inner sleeve, and wherein on each end a distal end of at least one string is fixed; and in that the diameter regulator device further comprises at least one means to modify the diameter of the adjustment strip, by pulling the opposite ends of said strings through a pulling system. flexible sleeve folded in its central area thus defining an inner sleeve and an external sleeve, and thus having a distal end and a proximal end, wherein the proximal end has at least two traction handles (10,11), the proximal ends of the inner sleeve and the external sleeve linked among each other, wherein the distal end and the proximal end are both open, and presenting in the distal end the fold which defines the inner sleeve and the external sleeve, and wherein the external sleeve has longitudinal pockets all along and its inner part to lodge the spatulas of the applicator, an applicator comprising a cup, spatulas that fit in the longitudinal pockets of the external sleeve and a guide indicator of the movement of the spatulas with respect to the cup, CHARACTERIZED in that: the diameter regulator device further comprises an adjustment strip having ends being made of a flexible material, and being formed into an open circumferential shape with a longitudinal opening between the ends, wherein the adjustment strip is placed between the inner sleeve and the external sleeve thereby encircling the inner sleeve, and wherein on each end a distal end of at least one string is fixed; and in that the diameter regulator device further comprises at least one means to modify the diameter of the adjustment strip, by pulling the opposite ends of said strings through a pulling system. the diameter regulator device further comprises an adjustment strip having ends being made of a flexible material, and being formed into an open circumferential shape with a longitudinal opening between the ends, wherein the adjustment strip is placed between the inner sleeve and the external sleeve thereby encircling the inner sleeve, and wherein on each end a distal end of at least one string is fixed; and in that the diameter regulator device further comprises at least one means to modify the diameter of the adjustment strip, by pulling the opposite ends of said strings through a pulling system.