Parental distress following newborn screening is thought to result from inadequate preparation for screening results which can result in maladjustment to screening results after birth. Although prior awareness of relevant genetic disorders such as cystic fibrosis and sickle cell diseases, and preparedness for screening is suggested to enhance information uptake and reduce parental distress, little is known about how young adults' prior knowledge prepares them for screening or affects the assimilation and retention of screening information. Thirty-four young adults, without familial genetic disease or screening experience took part in one of seven focus groups which examined knowledge of cystic fibrosis and sickle cell diseases and ability to assimilate new disease information. Thematic analysis revealed that adults had limited understanding of how cystic fibrosis and sickle cell diseases were inherited or how symptoms manifest, leaving them inadequately prepared for screening results if they do not engage with information interventions. Further, they selectively assimilated new disease information and had difficulty understanding new information in the absence of prior disease knowledge. Young adults' prior disease knowledge should be considered within a newborn screening context and written materials should consider the inclusion of carrier statistics to improve information relevance.