Iavnou's best finish at the FIS Nordic World Ski Championships was 13th in the 4 x 10 km relay at Sapporo in 2007 while his best individual finish was 36th in the 50 km event at those sam championships.
His best World Cup finish was ninth in a 4 x 10 km relay at Norway in 2009 while his best individual finish was 42nd in a 30 km event at France in 2006.