Data on the temporal dynamics of human placental gene expression is scarce. We have completed the first whole-genome profiling of human placental gene expression dynamics (GeneChips, Affymetrix) from early to mid- gestation (10 samples; gestational weeks 5 to 18) and report 154 genes with considerable change in transcript levels (FDR P<0.1). Functional enrichment analysis revealed >200 GO categories that are statistically over-represented among 105 genes with dynamically increasing transcript levels. Analysis in an extended sample (n=43; gestational weeks 5 to 41) conformed a highly significant (FDR P<0.05) expressional peak in mid-gestation placenta for ten genes: BMP5, CCNG2, CDH11, FST, GATM, GPR183, ITGBL1, PLAGL1, SLC16A10, STC1. A central hypothesis of our study states that the aberrant expression of genes characteristic to mid-gestation placenta may contribute to affected fetal growth, maternal preeclampsia (PE) or gestational diabetes (GD). The gene STC1 coding for Stanniocalcin 1 (STC1) was identified with a sharp placental expressional peak in mid-gestation, increased mRNA levels at term and significantly elevated STC1 protein levels in post-partum maternal plasma in all pregnancy complications. The highest STC1 levels were identified in women, who developed simultaneously PE and delivered an SGA baby (median 731 vs 418 pg/ml in controls; P=0.001). CCNG2 and LYPD6 exhibited significantly increased placental mRNA expression and enhanced intensity of immunohistochemistry staining in placental sections all studied in GD and PE cases. Aberrant expression of mid-gestation specific genes in pregnancy complications at term indicates the importance of the fine-scale tuning of the temporal dynamics of transcription regulation in placenta. Observed significantly elevated plasma STC1 in complicated pregnancies warrants further investigations of its potential as a biomarker. Interestingly, a majority of genes with high expression in mid-gestation placenta have also been implicated in adult complex disease. This observation promotes a recently opened discussion on the role of placenta in developmental programming.