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Prenatal detection of fetal thymidine kinase activity in maternal plasma: normal values and clinical application in
A Bieniarz1, H Kulaga, A L Medearis
1Department of Obstetrics and Gynecology, University of Southern California School of Medicine, Los Angeles.
Deoxythymidine kinase is present in human cells in two forms: the cytosolar form (fetal thymidine kinase) and the mitochondrial form (adult thymidine kinase). The activity of thymidine kinase isozymes in plasma of preterm and term newborns has been previously reported to be related to gestational age, and fetal thymidine kinase activity was reported to be undetectable after the thirty-ninth week of gestation. Our purpose was to determine if similar changes in the activity levels of the thymidine kinase isozymes could be demonstrated in late third trimester maternal plasma. A cross-sectional sample of 35 patients was studied from week 34 of pregnancy to delivery. Significant differences between fetal and adult thymidine kinase activity patterns were observed. Adult thymidine kinase activity remained relatively constant throughout the evaluation interval, while fetal thymidine kinase activity decreased with advancing gestational age. Regression analysis of gestational age by neonatal examination (GAPED) and fetal thymidine kinase revealed a linear relationship (fetal thymidine kinase = 0.380 - 0.00745 GAPED; R2 = 0.2944; standard estimate of error = 0.0350; p less than 0.0008). Comparison of fetal thymidine kinase activity in term and postterm pregnancy plasma revealed a significant difference (p less than 0.0159). Our findings indicate that deoxythymidine kinase activity can be measured in maternal plasma, may relate to the fetoplacental growth rate, and may be useful in differentiating between term and postterm gestations.
Deoxythymidine kinase is present in human cells in two forms: the cytosolar form (fetal thymidine kinase) and the mitochondrial form (adult thymidine kinase). The activity of thymidine kinase isozymes in plasma of preterm and term newborns has been previously reported to be related to gestational age, and fetal thymidine kinase activity was reported to be undetectable after the thirty-ninth week of gestation. Our purpose was to determine if similar changes in the activity levels of the thymidine kinase isozymes could be demonstrated in late third trimester maternal plasma. A cross-sectional sample of 35 patients was studied from week 34 of pregnancy to delivery. Significant differences between fetal and adult thymidine kinase activity patterns were observed. Adult thymidine kinase activity remained relatively constant throughout the evaluation interval, while fetal thymidine kinase activity decreased with advancing gestational age. Regression analysis of gestational age by neonatal examination (GAPED) and fetal thymidine kinase revealed a linear relationship (fetal thymidine kinase = 0.380 - 0.00745 GAPED; R2 = 0.2944; standard estimate of error = 0.0350; p less than 0.0008). Comparison of fetal thymidine kinase activity in term and postterm pregnancy plasma revealed a significant difference (p less than 0.0159). Our findings indicate that deoxythymidine kinase activity can be measured in maternal plasma, may relate to the fetoplacental growth rate, and may be useful in differentiating between term and postterm gestations.