Antenatal assessment of fetal age and maturity using fetal fat staining cells in amniotic fluid.

A cross sectional retrospective study of 400 cases of amniocentesis was performed to evaluate the reliability of using fetal fat staining cells as a method for assessment of fetal age and maturity. A sharp rise in the percentage of these cells in amniotic fluid occurred after 37 weeks of gestation and a level of 20 per cent or more indicated fetal age of 38 weeks or more, corresponding to maturity by our definition. The false positive and negative rates were 3.5 per cent and 14 per cent respectively. The pre-eclamptics, diabetics and Rh sensitized groups fell within the distribution of the normal population. The dysmature group, however, showed an earlier rise (20% at 36 weeks). The origin of the fetal fat staining cells and the reasons for the early rise in dysmaturity are discussed. Estimation of fetal fat staining cells in the amniotic fluids using the 20 per cent level is a reliable test for maturity in normal and some abnormal pregnancies, excluding dysmaturity.