Effects of therapy, antibody titer, and pregnancy history on pregnancy outcome were evaluated in pregnancies of women with antiphospholipid antibody. Prior fetal death and a high antiphospholipid antibody titer (greater than 40 IgG phospholipid units) contributed independently, in an additive manner, to current fetal loss. Twenty-one pregnancies occurred in asymptomatic women who had both prior fetal death and a high IgG antiphospholipid antibody titer. In this very high-risk group, 9 of 11 (82%) of pregnancies treated with prednisone, 10 to 60 mg/day, ended in fetal death, compared with 5 of 10 (50%) not treated with prednisone (p approximately 0.01, life-table analysis). Of pregnancies treated with aspirin, 80 mg/day, 9 of 14 (64%) treated and 5 of 7 (71%) not treated with prednisone had a fetal death (difference not significant). Prednisone does not improve, and may worsen, current fetal outcome in asymptomatic pregnant women with a high antiphospholipid antibody titer and prior fetal death.