environmental mechanisms must be influencing the association. Furthermore, similar to the adoption design described earlier, when significant associations are found among genetically unrelated parent-child dyads (i.e., where passive rGE is absent), the primacy of environmental mechanisms underlying this association is apparent. Last, by comparing parent-child associations between homologous IVF families and children born through surrogacy, because the former share genes, prenatal environment, and rearing environment whereas the later share only genes and rearing environment, prenatal environmental influences can be isolated. These between family differences permitted by examining IVF variations in genetic and prenatal relationship have high relevance for the design of preventive interventions, as discussed below.
