Objective To investigate the association between severe mid-trimester IUGR, whose causes are unknown in most cases, and maternal thrombophilias.

Design Case–control study.

Setting Lis Maternity Hospital, Tel Aviv Sourasky Medical Center, The Sackler Faculty of Medicine, Tel Aviv University.

Population Twenty-six women with severe mid-trimester (22–26 weeks of gestation) IUGR (birthweight <3rd centile) and 52 matched multiparous women with normal pregnancies (controls).

Methods After excluding pregnancies with vascular maternal disease, chromosomal and structural aberrations and cytomegalovirus infection, 26 women out of 35 with severe mid-trimester IUGR remained and composed the study group. Each was matched for age, ethnicity and smoking status with two healthy women who had normal pregnancies. All the women were tested for genetic and acquired thrombophilias at least eight weeks after delivery.

Main outcome measures Prevalence of maternal thrombophilias.

Results The frequency of thrombophilias was 69% in the study group compared with 14% in the control group [odds ratio (OR) 4.5; 95% confidence interval (CI) 2.3–9, P< 0.001]. The frequencies of factor V Leiden mutation, prothrombin gene mutation and protein S deficiency were significantly increased in the study group compared with the control group. The frequency of multiple thrombophilias was 33% in the study group versus none among the controls. Of the 26 pregnancies with severe mid-trimester IUGR, 13 ended in intrauterine fetal death before 25 weeks of gestation: 10 of these women had thrombophilia.

Conclusion Women with mid-trimester severe IUGR have an increased prevalence of inherited and acquired thrombophilias.