Objective: To assess the physiological changes in the placental expression pattern of a panel of genes related to angiogenesis and oxidative stress during the early part of the first trimester of pregnancy. Methods and Results: The expression of a selected panel of genes was quantified by reverse transcriptase-polymerase chain reaction in samples of villous trophoblasts obtained from women between 6 and 11 weeks of gestation undergoing elective artificial abortion. We found that the levels of messenger RNA (mRNA) expression of placental growth factor (PlGF), heme oxygenase 1(HO-1), and superoxide dismutase (SOD) increased significantly with gestational age (r = .37, P = .001; r = .24, P =.04; and r = .52, P < .001, respectively). Conversely, the mRNA expression level of fms-like tyrosine kinase 1 (FLT-1) decreased significantly (r=-.30, P = .009). Conclusion: During the early part of the first trimester of pregnancy, the placental gene expression levels of PlGF, HO-1, and SOD increase with gestational age, whereas the expression of FLT-1 decreases. The alteration in this pattern of gene expression in early pregnancy may therefore play an important role in placenta-related disorders such as preeclampsia. © The Author(s) 2013.