Low amniotic fluid is mainly associated with reduced production and increased leakage and absorption of amniotic fluid.
For example, reduced urination due to fetal kidney malformation can cause reduced fetal amniotic fluid production.
Premature rupture of membranes due to intrauterine infection can lead to increased leakage of amniotic fluid.
If the placenta is malfunctioning, this can cause a decrease in amniotic fluid production, which can lead to low amniotic fluid.