During the dynamic observation over a parturient woman in the second stage of labor it was registered that the fetal heart rate fell down to 90-100/min and didn't come to normal after contractions. Vaginal examination revealed the complete cervical dilatation, the fetal head filling the entire posterior surface of the pubic symphysis and sacral hollow; the sagittal suture lied in the anteroposterior diameter of the pelvic outlet, the posterior fontanelle was in front under the pubic arch. What plan for further labour management should be recommended?