Objectives: To measure the pressure of the amniotic cavity during pregnancy and to study the effects of antepartum amnioinfusion on oligohydramnios with intact membranes.
Method: We used an improved three-way switch apparatus to measure 110 women during pregnancy, and treated 97 oligohydramnios with antepartum amnioinfusion or intravenous infusion as controls.
Results: The pressure of the amniotic cavity was 1.69 +/- 0.23 kPa, which was close to the normal value in pregnancy. In oligohydramnios, it was 1.1 +/- 0.3 kPa, and in polyhydramnios 3.2 +/- 0.3 kPa(P < 0.01-0.001). When 300 ml fluid was amnioinfused, the amniotic fluid index (AFI) increased by 5.0 +/- 1.8 cm, the pressure of amniotic cavity increased by 0.18 +/- 0.2/kPa and the incidence of vaginal delivery was 87.9%, whereas that of the control group was 12.1%. There were no fetal distress, asphyxia neonatorum, amnionitis or ruptured membrane.
Conclusions: The pressure of the amniotic cavity during normal pregnancy was stable, but changed with AFI. Antepartum amnioinfusion for unruptured oligohydramnios resulted in a marked increase in incidence of vaginal delivery, a decreased ratio of cesarean section and a reduction of perinatal morbidity. These differences are highly significant.