Amniotic fluid was a clear liquid that surrounded a developing embryo, serving as a natural immune system. It could be studied via an amniotic scan.
In 2370, Lieutenant Commander Data used the amniotic fluid from the pregnant Alyssa Ogawa to develop a retrovirus against Barclay's Protomorphosis Syndrome. (TNG: "Genesis")
In 2401, Doctor Beverly Crusher, after realizing that the gravity well at the center of the Ryton Nebula was the "womb" of an space-dwelling organism, said that the USS Titan was "swimming in its amniotic fluid." (PIC: "No Win Scenario")