Fluid that surrounds the foetus in the amniotic sac.
Note: A specimen is obtained by a technique called amniocentesis, in which a long needle is inserted into the amniotic sac through the abdominal wall, through which fluid is withdrawn.
Source:
PAC, 2018, 90, 1121. 'Terminology of bioanalytical methods (IUPAC Recommendations 2018)' on page 1123 (https://doi.org/10.1515/pac-2016-1120)