An assessment of amniotic fluid volume has become an important component of antenatal testing for the at-risk pregnancy. The presence of normal amniotic fluid volume, either in association with a reactive nonstress test or as a component of the biophysical profile is considered to reflect current fetal well being and probable absence of chronic stress. The chronically stressed fetus is likely to have low amniotic fluid volume because of the shunting of blood preferentially to the brain, heart and adrenal glands at the expense of other body systems during the period of chronic stress. Decreased renal blood flow leads to decreased urinary output. Because the primary component of amniotic fluid in the third trimester of pregnancy is fetal urine, ongoing chronic stress can be recognised as oligohydramnios.

Precise amniotic fluid volume (AFV) measurement is accomplished either by use of a dye-dilution technique or by direct measurement of the fluid volume at the time of caesarean delivery. The need for laboratory support and the inherent invasiveness of dye-dilution procedures limits their application to study protocols. Direct measurement of AFV at caesarean delivery is reflective only of fluid volume at the time of delivery and cannot be used to serially evaluate fluid volume as a component of antenatal testing.