Amniotic fluid volume and normal flows to and from the amniotic cavity.

The regulation of amniotic fluid volume and composition remains largely unknown. Several difficult to study pathways exist for the formation (early transfer across fetal skin, fetal urine and lung fluid production) and removal (swallowing, transmembranous and intramembranous absorption) of amniotic fluid. It appears that flows across these pathways may work in concert the vast majority of the time because amniotic fluid volume is maintained within a normal range. When significant deviations occur from this normal range, especially in the mid trimester, significant perinatal morbidity and mortality incidence results.