approximately 200-250 words) Congenital defects are very heterogeneous in their classification, the occurrence of associated defects, their embryology and aetiology. Blastogenetic defects are ones that arise during the period of blastogenesis and involve the primary developmental field, which comprises the entire embryo from the time of conception to gastrulation. Blastogenetic defects result from various factors that disrupt the hierarchical molecular cascades that are responsible for patterning, leading eventually to the formation of progenitor fields and primordia. This group of disorders has been reported to be epidemiologically distinct from other congenital anomalies arising later in development. This study compares the epidemiology of blastogenetic and non-blastogenetic birth defects recorded in the Malta Congenital Anomalies Register during 1993 to 2001. Blastogenetic defects, which accounted for 9% of congenital anomalies, were associated with significantly higher proportions of foetal and neonatal deaths, higher mean maternal age and significantly lower mean gestational lengths and birth weight than babies with non-blastogenetic defects. Babies with defects of blastogenesis were homogeneous in their epidemiological characteristics. There were no significant differences among the group of babies with blastogenetic defects whether they occurred as isolated anomalies, MCA (multiple congenital anomalies) patterns, syndromes or chromosome anomalies. However, babies with isolated blastogenetic defects, showed significantly higher foetal and neonatal mortality rates, lower mean birth weights, and a higher proportion of premature births below 32 weeks than babies with non-blastogenetic isolated defects. Babies with MCA patterns including at least one blastogenetic defects showed significantly higher proportions of neonatal deaths and premature babies at or below 32 weeks, significantly lower mean birth weights and lower mean gestational length but no significant difference in foetal mortality as compared to their counterparts without blastogenetic defects