Amniotic fluid index

Amniotic fluid index (AFI) is an estimate of the amount of amniotic fluid and is an index for the fetal well-being. It is a part of the biophysical profile.

Leaking or rupture of membranes may be caused by a gush of fluid or a slow constant trickle of fluid. This is due to a tear in the membrane. Premature rupture of membranes can also result in low amniotic fluid levels.

Placental problems may cause low amniotic fluid. If the placenta is not providing enough blood and nutrients to the baby, then the baby may stop recycling fluid.

Birth defects may occur if the fetus has problems with the development of the kidneys or urinary tract, which could cause little urine production, and it can lead to low levels of amniotic fluid.

Maternal complications may cause low amniotic fluid. Some factors such as hypertension, diabetes, dehydration, preeclampsia, and chronic hypoxia in a woman can have an effect on amniotic fluid levels.

...
Wikipedia