Familial aggregation of stillbirth
Among stillbirth cases, we identified 2,498 (26.6%) probands with high-risk pedigrees (n=390), showing evidence for excess stillbirth familial aggregation (FSIR ≥2.00 and P-value <0.05) in the UPDB population (Table 1 ). Among high-risk pedigrees, the FSIR values ranged from 2.00 to 7.54 (Figure S2 ), indicating that the aggregation of stillbirth in the pedigrees is 2–8 times greater than what we would expect in the UPDB population by chance. A representative high-risk pedigree (pedigree #3 in Table 1 ) displayed in Figure 1 shows 10 stillbirth cases that descended from a common founder.