A 32-year-old woman, gravida 1, at the term of 38 weeks complains of irregular spastic pain in her lower abdomen and lumbar region. The pain is observed for 2 days, the patient did not sleep well at night. External obstetric examination detected increased tone of the uterus; the fetus is in the longitudinal lie, position the fetal head is position I, occiput anterior, the fetal head is mobile and located above the entrance to the lesser pelvis. Vaginal examination detects that the cervix is up to 2.5 cm, tilted backwards, unevenly softened, the external os is open to 0.5 cm, the internal os is closed. What is the most likely diagnosis in this case?