Right choice is (a) IUP
The best I can explain: The internal method measures intra-uterine pressure (IUP) via a fluid-filled catheter. The catheter is inserted into the uterus through a guide after the rupture of the foetal membranes. After allowing free flow of amniotic fluid to ensure correct placement, the distal end of the catheter is usually attached to a pressure transducer of the type used for cardiac studies.