In a significant departure from established criteria for population screening, a 2006 report by the American College of Medical Geneticists (ACMG) argued that newborn screening may be justified by family and societal benefits even if the screened infant does not stand to benefit. The ACMG report has since been the backdrop for considerable debate about the presumptive benefits of newborn screening. Understandings of family benefits have focused on how information provided by newborn screening may enhance reproductive decision-making, reduce the diagnostic odyssey, and alleviate the burden of raising a child with special health care needs. This paper identifies and describes an additional consequence of newborn screening for families. Specifically, we draw upon audio-recordings and clinical observations from a three-year ethnographic study of expanded newborn screening in California (November 2007-July 2010) to examine the potential for newborn screening to diagnose mothers with genetic disorders. This consequence of expanded newborn screening suggests the possibility of a different type of family spillover from that anticipated by the ACMG report. However, whether this knowledge benefits families depends on how the significance of genetic information is established in the clinic and the family’s ability to act on this information. We show that the newborn screening health care infrastructure is not designed to provide treatment for adult patients, so the identification of maternal disease does not necessarily prove beneficial for families.