Ultrastructural observations on amniotic fluid cells

Amniotic fluid was obtained at cesarean section from 5 third-trimester pregnancies and the proportion of orange-staining cells in the amniotic fluid determined using Nile blue sulfate staining. In the freshly obtained fluids 25 to 75 per cent of the cells stained orange. The cells were sedimented and processed for examination in the electron microscope. Virtually all the cells appeared to be squamous epithelial cells of fetal epidermis or mucous membrane. They contained variable numbers of keratin filaments and P.A.S.-positive particles resembling glycogen. No fat-containing cells were found. The presence of the squamous cells appeared to correlate with the thickening of the stratum corneum near term. It is concluded that the orange-staining cell is a cornified fetal squamous cell coated on its exterior surface by lipid material that appears to be intracellular in the light microscope and is removed during processing for electron microscopy.