PROS1 and hyperinsulinemic hypoglycemia, familial, 4: An increased risk of stillbirth has been reported in patients with protein S deficiency while the risk was not significantly increased in cases of protein C deficiency (Preston et al., 1996), and Kupferminc et al. (2002) found that protein S, but not protein C deficiency, was significantly associated with severe mid-trimester IUGR.