Pressure relationships between the intervillous space and the amniotic fluid in human term pregnancy

1.1. The intervillous space and the amniotic fluid pressures were recorded simultaneously and continuously for prolonged periods of time.2.2. As long as the uterus is not in active systole, the pressures in the two spaces remain virtually identical.3.3. Recording on a sensitive scale the pressure difference between the intervillous space and the amniotic fluid shows that during uterine systole the amniotic fluid pressure increases slightly faster than does the pressure in the intervillous space, the average maximum differential being approximately 2.6 mm. Hg. This pressure differential is partially “erased” by virtue of the fact that the pressure in the intervillous space makes up part of the pressure deficit by the time the apex of the contraction is reached.4.4. Movement of the patient brings about alterations in the pressure of approximately equal amounts in both spaces, and without appreciable lag. The amniotic fluid-intervillous space pressure relationship seems to be unaffected by either rupture of the membranes or the administration of oxytocin in physiologic dosage.