How can diclofenac potassium affect amniotic fluid from week 20 of pregnancy onward?

From pregnancy week 20 onward, diclofenac potassium (Voltarol) may reduce amniotic fluid through foetal renal dysfunction, sometimes shortly after starting treatment and usually reversibly after stopping; antenatal monitoring should be considered after several days of exposure, and treatment should stop if oligohydramnios is found.