Impact of intrauterine transfusion on fetal coagulation physiology by thromboelastography

Thromboelastography (TEG) is a point-of-care device used to evaluate whole blood coagulation function. The TEG is unique as a test of coagulation function in that it measures the interaction of all components of clot formation, which is different than traditional laboratory-based tests that measure isolated components of coagulation. Little is known about fetal coagulation physiology. We sought to evaluate the impact of severe fetal anemia and intrauterine transfusion (IUT) on fetal coagulation physiology by use of the TEG and to compare fetal TEG values to those of healthy neonates and adults.

One milliliter of fetal blood was collected immediately before (pre) and after (post) IUT of packed red blood cells (PRBCs). Sampling and transfusion were performed for fetal anemia due to hemolytic disease of the fetus and newborn. Samples were run in duplicate. For descriptive summary, duplicate pre-IUT and post-IUT values were averaged. Values for R (initiation of clot in minutes), K (clot firmness in minutes), angle (kinetics of clot development in degrees), and MA (maximum strength in mm) were obtained for each sample and presented using mean ± SE. Pre-IUT values for R, K, angle, and MA were compared with post-IUT values using linear mixed-effect model to account for clustering due to repeated observation from the same fetus. Pre-IUT values are compared with normal healthy term neonates and healthy adults using Wald test. The study was approved by the University of Pittsburgh Institutional Review Board (PRO14050051).

Four fetuses underwent nine IUTs rendering 17 pre-IUT and 17 post-IUT specimens. The mean gestational age at IUT was 31 weeks 2 days (25 weeks 4 days to 35 weeks 2 days). The mean IUT volume transfused was 69 mL (30-170 mL). The mean estimated percent intravascular volume transfused was 33.4% (19%-52%). Of the four variables analyzed, only R showed a significant difference, with the initiation of clot formation being modestly delayed after transfusion by an estimated 2.87 minutes (95% CI, 0.82-4.92, P = .0480). Pre-IUT values were compared with 100 normal term neonates and 118 healthy adults. Compared with pre-IUT, only R was affected (shorter) compared with term neonates (mean ± SE = 5.46 ± 0.16 minute, P < .001) and healthy adults (mean ± SE = 6.8 ± 0.13 minute, P < .001).

OTHER THAN A MODEST PROLONGATION OF CLOT FORMATION TIME, IUT OF PRBCS OF UP TO 52% OF THE ESTIMATED INTRAVASCULAR VOLUME DID NOT AFFECT FETAL COAGULATION FUNCTION BY TEG. OTHER THAN A SHORTER CLOT FORMATION TIME (R), THERE IS NO DIFFERENCE IN TEG VALUES BETWEEN ANEMIC PRETERM FETUSES AND HEALTHY TERM NEONATES AND HEALTHY ADULTS. BEYOND GENERALIZABLE KNOWLEDGE, THIS INFORMATION COULD BE EXPLOITED FOR FUTURE FETAL INTERVENTION TECHNIQUES.