Amniotic fluid cells in the second trimester of pregnancy.

The cell types of amniotic fluid in the second trimester of normal pregnancy are described and compared with the findings in the literature. Two hundred cell samples obtained by amniocentesis in pregnancies without known fetal neural tube or skin defects were studied. Anucleated and nucleated squamous epithelial cells of superficial and intermediate layers were found, as were macroforms of superficial cells. Parabasal cells were infrequent. Parabasallike cells were of amniotic origin. Other amniotic cell types, such as "balloon," or "goblet," cells, umbilical cord cells and hyperchromatic placental amniotic cells, were observed. Urothelial cells and nonepithelial cells, such as histiocytes and macrophages, were found. In several cases, "minicells" were seen; their different sites of origin are discussed.