Clinical meaning
Amniotic fluid is a dynamic biological medium that surrounds the fetus within the amniotic membrane throughout pregnancy. Its volume is regulated by a continuous cycle of production and reabsorption involving multiple fetal organ systems. In early pregnancy (before 16 weeks), amniotic fluid is produced primarily by filtration across the fetal skin and the amniotic membrane from maternal plasma. After fetal skin keratinization occurs at approximately 20 weeks, the two primary sources of amniotic fluid become fetal urine production and fetal lung fluid secretion. The fetal kidneys begin producing urine by 10-12 weeks gestation, and by the third trimester, fetal urinary output accounts for the majority of amniotic fluid production, contributing approximately 800-1200 mL per day at term. Fetal lung fluid contributes approximately 170-200 mL per day. Amniotic fluid is removed primarily through fetal swallowing (approximately 500-1000 mL per day at term) and absorption through the fetal membranes and across the fetal surface of the placenta (intramembranous pathway). The balance between production and removal maintains a normal amniotic fluid volume that peaks at approximately 800-1000 mL at 36 weeks gestation, then...