Amniotic fluid and the fetal mucosal immune system

This chapter reviews the development of the chorionic and amniotic cavities and the synthesis, composition, and fate of amniotic fluid. Amniotic fluid-the solution contained within the amniotic membranes-surrounds the developing fetus from about the sixth week of gestation until immediately before birth, when the fluid is released. The potential sources of chorionic and amniotic fluids thus include-fetally derived constituents from the external and mucosal surfaces of the fetus, maternally derived constituents from the deciduas, and the maternal blood in the intervillus spaces of the placenta across the overlying chorioamniotic membranes. Immune-related factors in amniotic fluid play roles in defense of the fetal and uterine structures against infection, signaling the uterus that the fetus has sustained an infection, initiating parturition, and/or modulating the maternal immune response to prevent rejection of the fetus. Amniotic fluid complement factor C3 can be used in the diagnosis of intra-amniotic infection in preterm labor with intact membranes. Assays for C3 are available readily, and their results compare favorably with other rapid markers such as white blood cells, lactate dehydrogenase, and glucose as an indicator of amniotic fluid infection.