Intrauterine growth restriction (IUGR) depends on the placental capacity to transfer oxygen and nutrients from the maternal to the fetal circulation. Placental insufficiency may be caused by impairment of the maternal or fetal circulation by a thrombotic event, possibly associated with thrombophilic disorders. The goals of our study were to define the role of maternal/fetal gain-of-function factor V Leiden and prothrombin G20210A mutations in the development of IUGR and to evaluate whether maternal pregnancy-induced hypertensive diseases would modify any such association. This is a case-control study: controls were 259 normal pregnancies, cases were 77 IUGR, 28 with and 49 without preeclampsia (PE) or pregnancy-induced hypertension (PIH). An association was found between IUGR and fetal thrombophilia (OR 2.09 CI 95% 1-4.5). The association was stronger in IUGR without PE and PIH (OR 2.9 CI 95% 1.3-6.6). This suggests a role for the fetal genotype in the development of IUGR.