Alternative method of gestational age assessment by the measurement of human erythrocyte differentiation antigen expression.

Standard estimates of gestational age are dependent on such subjective data as maternal recollection of last menstrual period, ultrasound examination of the fetus, and the postnatal physical and neurological examination (Ballard score). We hypothesized that a quantitative, objective laboratory test using flow cytometric analysis of erythroid differentiation antigens could be useful to predict gestational age. For this study erythrocyte samples were obtained within 24 hours of birth from 25 infants (gestational ages 20 to 41 weeks) who met the criteria that traditional estimates of gestational age, such as the Ballard score, fetal ultrasound, and maternal estimate of last menstrual period all agreed within 1 week for the assessed infant's gestational age. Study measurements included reticulocyte count and determination of the percentage of erythrocytes that expressed the 5F1 and 20.3 erythropoietic differentiation antigens. Linear regression analysis indicated that the best correlations with gestational age were reticulocyte count (R2 = .354) and the reciprocal of the percentage of erythrocytes expressing the 5F1 antigen (R2 = .470). When both variables were incorporated into a linear regression model, the predictability of gestational age achieved an R2 = .608. Through this study we have established the feasibility and methodology of using fetal and newborn erythrocytes to provide an objective assessment of gestational age by flow cytometric analysis of erythroid differentiation antigen expression. This methodology will allow for an independent assessment of gestational age when fetal blood sampling is performed for other prenatal diagnostic studies. Further investigation is needed to identify other erythroid differentiation markers that would improve the accuracy of our model to predict gestational age.