Normal amniotic fluid volume changes throughout pregnancy.

The purpose of this study was to provide a quantitative characterization of the changes in amniotic fluid volume that occur throughout gestation. From 705 published amniotic volumes for normal pregnancies, we found that after log transformation, amniotic fluid volume had a uniform variability over 8 to 43 weeks' gestation. Thus the 95% confidence interval covered the range of 1/2.57 to 2.57 times the mean volume at any given gestational age. Contrary to expected trends, mean amniotic fluid volume did not change significantly between 22 and 39 weeks and averaged 777 ml, with the 95% confidence interval ranging from 302 to 1997 ml. The data are summarized in nomograms covering 8 to 43 weeks' gestation.