Solved. There might be a more elegant way, but this worked:
DECLARE @ID Table (ID int);
INSERT INTO Table1 (FIELD1, FIELD2, FIELD3)
output Inserted.IDFIELD INTO @ID
Select 1,2,3
where not exists (SELECT 'x' FROM Table1 T1 WHERE T1.FIELD1 = 1 AND T1.FIELD2 = 2;
INSERT INTO Table2 (Other1_theID, Other2, Other3)
(Select ID,'A','B'from @ID
where not exists (SELECT 'x' FROM Table2 T2 WHERE T2.Other2 = 'A' AND T2.Other3 = 'B')) UNION ALL
(Select ID,'C','D'from @ID
where not exists (SELET2 'x' FROM Table2 T2 WHERE T2.Other2 = 'C' AND T2.Other3 = 'D')) UNION ALL
(Select ID,'E','F'from @ID
where not exists (SELET2 'x' FROM Table2 T2 WHERE T2.Other2 = 'E' AND T2.Other3 = 'F'))