While the four diagnostic systems essentially agree on criteria for fetal alcohol syndrome (FAS), there are still differences when full criteria for FAS are not met. This has resulted in differing and evolving nomenclature for other conditions across the spectrum of FASD, which may account for such a wide variety of terminology. Most individuals with deficits resulting from prenatal alcohol exposure do not express all features of FAS and fall into other FASD conditions. The Canadian guidelines recommend the assessment and descriptive approach of the "4-Digit Diagnostic Code" for each key feature of FASD and the terminology of the IOM in diagnostic categories, excepting ARBD.