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The cellular content of amniotic fluid is primarily composed of desquamated fetal cells of two origins, squamous and sebaceous, readily differentiated by staining with Nile blue sulphate. Ninty-two cases of amniotic fluid obtained by amniocentesis or forewater amniotomy have been studied at various stages of gestation and in the first stage of labor. With Nile blue sulphate, the squamous cells are stained light blue with dark blue nuclei and "lipid laden cells", shed from sebaceous gland, are stained orange in color. Results are as follows; 1. Percentage of "fat cells" began to increase around 36th week of gestation and sharply increased after 38the week of gestation. 2. After 36th week of pregnancy, the majority of the cases showed 20 percent or more of fat cells. 3. When the fat cell counts were more that 20%, the birth weights were over 2,500 grams in majority of cases. 4. There was no difference in the percentage of fat cell between two amniotic sacs in twin while marked difference in birth weight was noted. 5. There was no significant difference in the percentage of fat cell between normal and toxemic pregnancy of similar gestational age. If the estimation of fetal age is needed, particularly in cases with unreliable menstrual history or controversial physical findings, cytologic study of the amniotic fluid would be of valuable guide to the estimation of fetal maturity.
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