Uterine Fluid in Pregnancy: A Biological and Clinical Outlook.

Once considered a simple medium for sperm and embryo transport, the functional spectrum of uterine fluid is now expanding. Novel molecular players, such as extracellular vesicles and mobile RNAs, have been detected in the uterine fluid of livestock, rodents, and humans. These novel molecules, together with previously known ions and proteins, ensure uterine fluid homeostasis and facilitate embryo-maternal interactions. Here, we propose that these molecules may also carry information that mirrors maternal environmental exposure and possibly relay such information to the embryo via uterine fluid, generating long-term epigenetic effects on the offspring via embryonic and placental programming. Moreover, the development of systematic profiling of uterine fluid molecular signatures may now hold promise, relying on high-throughput methods and non-invasive biomarkers for clinical use.