Amniotic fluid was a liquid substance defined by the Twelfth Doctor as "the stuff that life comes from." (TV: Kill the Moon) The Fourth Doctor once called primordial soup "amniotic fluid". (TV: City of Death)
Both Humans (PROSE: Infinite Requiem) and Arboretans (PROSE: Festival of Death) developed in amniotic fluid prior to being born.
The Tenth Doctor compared clone feed to amniotic fluid for Sontarans. (TV: The Poison Sky)
The Moon contained amniotic fluid, as it was the egg of an enormous creature. (TV: Kill the Moon)
The Yzashoks existed in an amniotic fluid that responded intimately to their brain patterns. (PROSE: Infinite Requiem)
In 1827, Baron Teufel tried to create life by lowering a cadaver into a vat of warm amniotic fluid and charging it with electricity. (AUDIO: The Beast of Orlok)
In the 1890s, the Darkling Façade could control the minds of others when its amniotic fluid came into contact with them. (AUDIO: Jago & Litefoot & Patsy)