Total RNA was isolated from placental samples using Trizol reagent followed by DNase treatment. cDNA was synthesized. Real-time PCR was done according to the manufacturer's protocol (Fermentas, CA) by using ABI 7500 instrument. OPN primers were as follows: forward, 5′-GAACATGAAATGCTTCTTTCTCAG-3′; reverse, 5′-TCCATGAAGCCACAAACTAAACTA-3′. Real-time PCR reactions were performed in 25 μl volumes, containing 1 μl cDNA. All samples were performed in triplicate for 40 cycles of PCR under the following conditions: initial enzyme activation and template denaturation for 10 min at 95 °C followed by 10 s at 95 °C, 20 s annealing at 60 °C and extension phase for 35 s at 72 °C. OPN were normalized to the mRNA levels of housekeeping gene GAPDH.