Purpose of investigation: We studied the relation of first trimester nuchal translucency and first trimester biochemical markers using low molecular weight heparin (LMWH) at 11-14 weeks of gestation. Methods: This retrospective study was conducted at our university between January 2007 and July 2009. Ninety-six patients were treated with low-dose LMWHs (enoxaparine 40 mg) from the beginning of pregnancy to 36 weeks of gestation and low-dose aspirin (100 mg) to 32 weeks (group 1) and 100 control subjects (group 2) were included in the study. Transabdominal ultrasound examination was performed to diagnose any major fetal defects and for measurement of crown rump length (CRL) and fetal nuchal translucency (NT) thickness. Blood samples were drawn from each women PAPP-A and free beta hCG levels. Results: There were no significant differences with respect to age, gestational age at the first trimester, and gestational age at birth between the groups. The mean birth weight of babies in the LMWH group was lower than the control (p = 0.026). There were also no significant differences with respect to CRL, serum PAPP-A and hCG at 11- 14 weeks of gestation. However, NT of group 1 was significantly lower than group 2 (p = 0.000). In the Spearman correlation, LMWH was negatively correlated with only NT (r = –0.298, p = 0.000). NT in the first trimester (95% CI –0.632-0.230, p = 0.000) was an independent parameter related to using LMWH. Conclusion: Women who used LMWH during pregnancy had decreased NT compared with unaffected women.;">