Origin and function of amniotic fluid albumin: a review of the available evidence

Little is known about the origin of albumin in amniotic fluid. A fetal origin is questionable, because of the low concentration of protein in fetal urine and lung fluid. A maternal origin of proteins in amniotic fluid was already proposed in the 1970s. This review focuses on the possible sources of albumin in amniotic fluid and on the pathways for albumin to enter and leave the amniotic fluid in the second and third trimester. Based on the available evidence, it is unlikely that the fetus makes a large contribution to amniotic fluid albumin. Maternal albumin probably reaches the amniotic fluid through the fetal membranes, though the amniotic membrane itself also produces albumin. The functions of albumin in amniotic fluid are even less understood. Albumin may influence the homeostasis of amniotic fluid volume. Furthermore, intake of albumin, and the fatty acids which albumin carries, could be a substantial part of fetal nourishment. More knowledge on the mechanisms that determine amniotic fluid composition and on the function of albumin in amniotic fluid could provide the basis for new fetal therapy strategies.