A 22-year-old woman, gravida 1, para 0 arrived with complaints of sharply painful contractions that occur every 4-5 minutes and last for 25-30 seconds. Amniotic fluid did not burst. The fetus is in transverse lie, fetal heartbeats are not affected. Contraction ring is acutely painful, located obliquely at the umbilicus. What is the most likely diagnosis?