Sitras et al. investigated the differences in global gene expression profile between first and third trimester normal human placentas. Placental samples were collected from 21 women with uncomplicated pregnancies delivered at term and 16 healthy women undergoing termination of pregnancy at 9–12 weeks gestation. All women were healthy, Caucasian, and had low risk pregnancies. Chorionic tissue was dissected approximately 2 cm beside the umbilical cord insertion site, from the middle layer of placenta midway between maternal and fetal surfaces.
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