The specific aim of the current study of 133 women with at least 1 pregnancy and measures of hypofibrinolytic and thrombophilic gene mutations was to determine retrospectively whether the mutations were associated with adverse pregnancy outcomes including prematurity, miscarriage, stillbirth, intrauterine growth retardation (IUGR), eclampsia, and abruptio placentae. Four gene mutations (factor V Leiden, methylenetetrahydrofolate reductase [MTHFR], prothrombin, and 4G/5G polymorphism of the plasminogen activator inhibitor type 1 [PAI-1] gene) were assessed by polymerase chain reaction (PCR). One hundred twenty-two women were genotyped for all 4 genes and divided into gene mutation (n = 68) and non-gene (n = 54) groups. The gene mutation group included those with at least 1 thrombophilic mutation (heterozygous for factor V Leiden, heterozygous for prothrombin, and homozygous for MTHFR), or hypofibrinolysis with homozygosity for the 4G polymorphism of the PAI-1 gene. The non-gene mutation group included those with no mutation for all 4 genes (wild-type normal) or who were wild-type normal for the prothrombin and factor V Leiden mutations and heterozygous for MTHFR and/or 4G/5G for the PAI-1 gene, neither heterozygosity associated with coagulation abnormalities. The 68 women with gene mutations, versus 54 in the non-gene mutation group, has more prematurity (10% v 4%, chi2 = 5.4, P = .021), more IUGR (3% v 0%, P = .035), and more total complications of pregnancy (37% v 21%, chi2 = 11.6, P = .001). The number of pregnancies (P = .0001) and 4G/4G polymorphism of the PAI-1 gene (P = .029) were positively associated with complications of pregnancy by stepwise logistic regression when the age, number of pregnancies, and all 4 gene mutations were the explanatory variables. Heritable hypofibrinolysis, mediated by 4G/4G homozygosity for the PAI-1 gene, is an independent significant, potentially reversible risk factor for pregnancy complications, probably acting through thrombotic induction of placental insufficiency.