pathology Amniotic fluid and fetal cells enter the maternal circulation, possibly triggering an anaphylactic reaction to fetal antigens a(1) Clinical symptoms result from mast cell degranulation with the release of histamine and tryptase, (2) Clinical symptoms result from activation of the complement pathway.pathology ◼ Amniotic fluid and fetal cells enter the maternal circulation, possibly triggering an anaphylactic reaction to fetal antigens. ◼ (1) Clinical symptoms result from mast cell degranulation with the release of histamine and tryptase, ◼ (2) Clinical symptoms result from activation of the complement pathway