Intrauterine growth restriction is an important cause of morbidity and mortality. Its pathogenesis is still a matter of debate. The aim of this study was to evaluate the association between intrauterine growth restriction (diagnosed in utero by serial ultrasound examinations and characterized by abnormal umbilical arterial Doppler velocimetry) and thrombophilic polymorphisms (factor V Leiden, prothrombin G20210A) or methylenetetrahydrofolate reductase C677T carried by mothers and/or neonates.This was a case-control study with prospective enrollment. Fetuses with intrauterine growth restriction were included if they had three characteristics: 1) reduced intrauterine growth (measured in utero by ultrasound); 2) birth weight below the 10th percentile; 3) abnormal Doppler velocimetry of the umbilical artery. The three polymorphisms were evaluated in 48 cases and in 98 controls by polymerase chain reaction (PCR) and restriction analysis.Factor V Leiden was present in 2/48 (4%) mothers or neonates among cases and 7/98 (7%) among controls. Prothrombin G20210A was present in 0/48 (0%) mothers or neonates among cases and 4/98 (4%) among controls. Methylenetetrahydrofolate reductase C677T was present in 16/48 (33%) mothers or neonates among cases and 22/98 (22%) controls. Overall the prevalence of the polymorphisms in mothers and/or neonates was 18/48 (37%) in cases and 33/98 (34%) in controls.No association was found in this study between intrauterine growth restriction with abnormal umbilical blood flow and thrombophilic polymorphisms or methylenetetrahydrofolate reductase C677T.