Data and sample collection
Couples received saliva sample and buccal swab kits to collect cells for DNA sampling with instructions along with a brief questionnaire for demographic data collection. Research team and obstetricians examined patient clinical and demographic data and entered the data in REDcap. Couples provided spit saliva and buccal saliva from their live-born children. Placenta samples from pregnancies that resulted in fetal demise were processed by pathology within three days of delivery. One family with a known aneuploid stillbirth (Family 3) was included since they had five unexplained losses (Table S1 ). Placentas were processed using clinical protocols for placental pathology, and samples were obtained from formalin fixed and paraffin embedded (FFPE) blocks and stored at room temperature. In some cases, samples were collected for research only. In these cases, placentas were washed and dissected from fetal villi and maternal decidual tissue to ensure sampling of fetal tissue. Tissue from these samples were divided into aliquots and stored at -80 oC.