Pound Pup Legacy

"twin studies show approximately a 50% risk of developing schizophrenia in identical twins (meaning siblings with exactly the same genes), environment must have significant influence in the brain disorder.  A well-designed, 40-year longitudinal study from Finland focused on identifying the degree to which family environmental factors might play a protective role in those who are genetically susceptible to schizophrenia. 

Identification of family environmental factors that are protective against developing  schizophrenia offers significant hope for those predisposed to this brain disorder.  Such protective factors indicates that preventive measures may be taken by parents to reduce the likelihood that their child will develop schizophrenia.  Based on the results of this study, there are significant protective family environmental factors that may reduce the schizophrenia risk for a susceptible child by up to 86%.  

Some children, due to their genetics (as well as prenatal environment and stress prior to birth), are much more sensitive to certain environmental factors and stress, and as a result of this are more likely to develop schizophrenia.  Adoptees with high-genetic risk for schizophrenia-spectrum disorders (see below) have been found to be more sensitive to environmental effects than adoptees with low-genetic risk for the disease".  http://www.schizophrenia.com/familyenv1.htm

My question is this:  How can any social worker/adoption agency predict the future family dynamic of any given family?  Furthermore, do these studies consider the stress adoption has on the pregnant mother?