The great arteries in normal and some congenitally malformed hearts their internal calibres and tunica media in relation to blood flow

The road from fertilized egg to newborn baby is a fascinating and complicated one. What happens to eggs that actually come in contact with spenns has been stuclied by many authors and has been summarized by Witschi in 1969. About 16% of the eggs do not cleave, either because they are not penetrated by sperms or because the mitotic mechanism does not function. Another 15% are lost during the first week, at various preimplantation stages ( cleavage and blastocyst stages ). The stage of early implantation and development during the second week brings a further lossof 27%. In the third to sixth week there is a loss of 8% and the late abortion loss is about 3%. Live births will then amount to only 31%. It has been shown that 1-12% of all these newborn children carry some major congenital malformation recognizable at or shortly after birth ( Yerushalmy, 1969; Lilienfeld, 1969 ), Reports of congenital malformations show congenital heart malformations in about 0.8% of total births ( Kerrebijn, 1964; Hoffman and Christianson, 1978 ). In the Netherlands with 177.090 newborns in 1976 this will be about 1400 per year of which 123 were surgically corrected and 416 died in the first year of life ( Centraal Bureau voor Statistiek, 1976, 1978 ). The majority of congenital he'art malfonnations are of rmknown etiology and are believed to be the result of the interaction of environmental and genetic influences ( Nora, 1968 ). The risk for recurrence of the same lesion in cases with an affected parent or sibling is small but exceeds the expectation risk for the same lesion in the general population. Vertical transmission of atrial septal defects through four generations has been described (Lynch et al., 1978 ) . These children bom with congenital heart malfonnations are of special interest to the paediatric cardiologist and cardiovascular surgeon.