Sonographic assessment of amniotic fluid in normal twin pregnancy.

A sonographic standard for assessment of amniotic fluid volume in normal twin pregnancy is provided. In 210 uncomplicated twin pregnancies, amniotic fluid volume was assessed sonographically, by measuring the total amniotic fluid index (AFI), as well as the deepest single vertical pocket in each sac. The mean AFI was greater than values found in singleton gestations; the AFI increased up to 27 weeks' gestation, and decreased thereafter. It correlated well with measurement of the deepest vertical pocket in each sac (r = 0.71; p < 0.0001). In twin pregnancy at 26 to 32 weeks' gestation a fluid pocket of at least 8 cm was found in 9.8% of cases and did not indicate pathologic states. Either AFI or measurement of the deepest fluid pocket in each sac can be used to assess fluid volume in twin pregnancy. A table specific to twin pregnancy should be used when evaluating twin gestations sonographically.