Equalization of amniotic fluid volumes after decompression amniocentesis for treatment of the twin oligohydramnios-polyhydramnios sequence

Objective: To measure acute and chronic changes in the placenta and amnioti c fluid associated with performance of decompression amniocentesis in pregn ancies with the twin oligohydramnios-polyhydramnios sequence (TOPS). Method s: Amniotic fluid pressures, placental thickness, placental perfusion, and amniotic fluid volumes were measured in each sac of a monochorionic diamnio tic twin gestation before and after decompression amniocentesis. Indigo car mine was injected into the polyhydramnic sac after decompression, and fluid from the oligohydramnic sac was sampled after equilibration. Spectrophotom etric analysis of amniotic fluid specimens was performed for dye detection. Amniotic fluid volume and placental perfusion studies were repeated 1 week later. Results: Three patients with TOPS were enrolled, and decompression amniocentesis was performed in the midtrimester, After decompression, amnio tic fluid volume decreased in the polyhydramnic sac, amniotic fluid pressur es decreased in both sacs, placental thickness increased, and umbilical art ery Doppler velocimetry was unaffected. The amniotic fluid volume increased acutely in only one oligohydramnic sac after decompression, and ultrasonog raphic examination, amniotic fluid spectrophotometric analysis, and placent al pathologic examination all identified interfetal membrane disruption as the etiology. Conclusions: Decompression amniocentesis as a treatment for T OPS does not result in acute or chronic changes in the amniotic fluid volum e of the oligohydramnic sac in the absence of interfetal membrane disruptio n.