When mothers go to the hospital for checkups, they may be told that their amniotic fluid is insufficient, so what exactly are the causes of amniotic fluid deficiency? 3. If the pregnancy has exceeded 42 weeks and delivery cannot be initiated, it can also cause low amniotic fluid. 4. Some pregnant women, for various reasons, suffer from placental hypofunction and placental calcification during pregnancy, which are common causes of low amniotic fluid.