Thrombopoietin levels in cord blood plasma and amniotic fluid in fetuses with alloimmune thrombocytopenia and healthy controls

To extend our knowledge of the kinetics of fetal thrombopoietin (TPO), we s tudied TPO levels in cord blood plasma and amniotic fluid collected from 15 fetuses considered to be at risk of fetomaternal alloimmune thrombocytopen ia and also from 10 healthy controls at caesarean delivery. In the plasma o f all 25 fetuses and newborn infants studied, TPO was detected above the lo wer limit of detection (7 pg/ml) and correlated inversely with platelet cou nts (r = -0.53, P = 0.006). At term, TPO detected in amniotic fluid was at significantly lower levels (7 pg/ml: range 0-22 pg/ml) than simultaneously obtained cord plasma TPO (114 pg/ml: range 43-201 pg/ml: P < 0.001). There was no correlation between levels of TPO in amniotic fluid and cord plasma or platelet counts. the serial samples collected from the five fetuses with HPA-1a alloimmunization before 37 weeks' gestation, the TPO levels in amni otic fluid were significantly higher than at term (P = 0.013): from 22 to 2 8 weeks' gestation, 42 pg/ ml (30-78 pg/ml): from 31 weeks', 24 pg/ml (17-3 3 pg/ ml): at term, 8 pg/ml (4-13 pg/ml), correlating inversely with gestat ional age (r = -0.81, P = 0.003). Thus, TPO is present in amniotic fluid at levels apparently inversely related to gestational age, Whether these high levels seen early in pregnancy are normal or are associated with the HPA-1 alloimmunization remains to be shown.