Plasma elimination of antithrombin III (heparin cofactor activity) is accelerated in term newborn infants

Effect of delivery modalities on the physiologic inhibition system of coagulation of the neonate

The perinatal period is associated with an increased incidence of thromboembolic complications, which may occur in both the maternal and fetal circulation in otherwise normal and healthy adults and fetuses, and this may be related to the activation of the coagulation system at the time of parturition. The risk of these complications is generally much higher in neonates, who have decreased activity of the physiologic inhibition system of coagulation (PISC), including protein C, protein S and antithrombin, in comparison with adults. Therefore, any additional obstetric iatrogenic factors could predispose the neonate to an increased risk of thromboembolic complications. The aim of this study was to evaluate the influence of modality of delivery (spontaneous vaginal delivery vs. elective caesarian section) on the neonatal PISC factor (protein C, protein S and antithrombin) levels and the fibrinolytic system (plasminogen and fibrinogen levels). We studied 41 consecutive healthy newborns, 18 delivered vaginally (mean gestational age 39.7 +/- 0.8) and 23 by elective caesarian section (mean gestational age 38.5 +/- 0.7). Plasma samples were collected from the umbilical cord at birth. AT activity, protein C antigen and activity, total and free protein S antigen, fibrinogen concentration and plasminogen activity were tested. Among PISC factors studied in cord blood of infants born after vaginal delivery, protein C antigen levels and antithrombin activity were statistically higher (41.3 +/- 9.4 vs. 33.9 +/- 7.2 and 58.5 +/- 10.0 vs. 48.4 +/- 12.7, respectively; P<.01), while free protein S was significantly lower (36.8 +/- 11.6 vs. 46.4 +/- 12.5; P<.05) than in newborns delivered by caesarian section. Cord blood plasminogen and fibrinogen were elevated in vaginally delivered neonates in comparison to those delivered by caesarian section, but the difference was not statistically significant. Our data show that the labor stress of vaginal delivery may play a role in influencing the levels of some PISC factors in the cord blood of full-term neonates. In newborns with coagulation disorders, separate reference ranges in coagulation screening tests should be possibly needed depending on the delivery modality.

Functional maturity of the coagulation system in children: an evaluation using thrombelastography

There are quantitative deficiencies in the coagulation system for at least the first 6 mo of life. Clinical experience, however, does not indicate an increased risk of excessive bleeding during surgical procedures. Thrombelastography, a test providing a functional evaluation of coagulation, was used to assess the hemostatic system of pediatric patients under 2 yr of age. Thrombelastographic data were obtained from 237 healthy pediatric patients less than 2 yr of age undergoing elective noncardiac surgery. Five groups were distinguished: under 30 days, 1-3 mo, 3-6 mo, 6-12 mo, and 12-24 mo. Thrombelastography revealed no defects in coagulation when these groups were compared to each other or to adults, indicating a functionally intact hemostatic process even in neonates. Indeed, children less than 12 mo of age were found to initiate and develop clot faster than adults, with the coagulation process slowing to adult rates after 1 yr of age. In addition to defining functional integrity, our data represents a set of pediatric control thrombelastographic values that have not been previously reported and that may become important in understanding coagulation changes that accompany disease states and surgery in pediatric patients.

The relevance of developmental hemostasis to hemorrhagic disorders of newborns

The hemostatic system is a dynamic evolving process that is age-dependent. Components of the hemostatic system are synthesized in early fetal life and do not cross the placenta from mother to fetus. However, plasma concentrations of proteins involved in hemostasis significantly differ from adults. Physiological reference ranges are available for premature infants, full-term infants and children from ages 1 to 16 years. In the coagulation system, plasma concentrations of the vitamin K-dependent and contact factors are decreased at birth, whereas other factors such as fibrinogen, FV, FVIII, and FXIII are similar or increased compared with adults at birth. In the fibrinolytic system, plasma concentrations of plasminogen are decreased at birth, whereas tissue plasminogen activator and plasminogen activator inhibitor are increased. Clinically, the hemostatic system of the young is effective and healthy infants do not suffer from spontaneous hemorrhagic complications. However, infants are more vulnerable, compared with older patients, for bleeding in the presence of either congenital or acquired haemostatic defects. Severe congenital bleeding disorders, although rare, frequently present in the newborn period. The most common acquired causes of bleeding newborns include disseminated intravascular coagulation, vitamin K deficiency, and liver disease. A description of these disorders and treatment guidelines are provided.

Developmental expression of chicken antithrombin III is regulated by increased RNA abundance and intracellular processing

We isolated and sequenced a 432 bp cDNA to cAT-III, that encoded 115 nucleotides of 5' untranslated sequence, a 17 amino acid long signal peptide and residues 1-88 of the mature protein, and used it to prepare a probe for measuring and correlating the developmental changes of steady-state cAT-III mRNA levels with known changes in antigen levels. Densitometric analysis of nuclease protection (n = 2), Northern blot (n = 4), and slot blots (n = 3) of total RNA from chick livers of 16-day-old embryos to 6-day-old chicks showed a 2.6 +/- 0.5-fold increase in steady-state cAT-III mRNA levels. Assay of functional mRNA levels by in vitro translation of poly(A)+ RNA and specific immunoprecipitation of 35S-Met-labelled cAT-III was comparable to RNA analysis (16-day-old embryos vs. 10-day-old hatchlings). We evaluated whether there were developmental differences in post-translational secretion which may also contribute to the regulation of the circulating level of this protein. Pulse-chase studies of freshly-isolated hepatocytes from 16-day-old embryos and 10-day-old hatchlings maintained in suspension demonstrated a approx. 5.0-5.5-fold increase in cAT-III levels at steady-state secretion. The above findings indicate that changes in circulating cAT-III levels during late embryonic development are primarily due to increased abundance of cAT-III mRNA. In addition, we postulate that post-translational intracellular processing may account for further differences in circulating protein levels.

Comparison of antithrombin III, protein C and protein S levels in capillary and venous blood of newborn infants

The plasma concentrations of antithrombin III, protein C and protein S in capillary and venous blood samples obtained simultaneously from 30 neonates were compared in order to determine the suitability of using capillary blood for estimation of these proteins with anticoagulant action. Our findings showed that while capillary and venous blood did not differ significantly in antithrombin III functional activity and protein C antigen levels, the capillary samples had significantly lower protein C functional activity and higher antithrombin III antigen level. Protein S antigen level was also significantly higher in the capillary samples although the difference was relatively small. The capillary and venous concentrations of the binding protein of protein S, C4b binding protein, were almost identical.

Low antithrombin III in neonatal shock: DIC or non-specific protein depletion?

Low antithrombin III (AT III) levels in shock are usually ascribed to disseminated intravascular coagulation (DIC). However, decreased activities of clotting factors and their inhibitors could reflect a generalised fall in plasma proteins rather than DIC. AT III and albumin were compared in 48 asphyxiated and non-asphyxiated newborn rabbits (pH 6.70-7.30). Both AT III and albumin were markedly decreased in the sickest animals and there was a direct linear relationship between the two proteins (P less than 0.001). Similar results were obtained in ten newborn infants suffering from shock and haemorrhagic diathesis. In all cases AT III and albumin were decreased below the normal range and significantly correlated (P less than 0.01). Our findings suggest that AT III is not a useful diagnostic marker of DIC. Further, a similar fall of clottable and non-clottable proteins in shock questions the general assumption that the ensuing coagulopathy is due to intravascular coagulation.

Anticoagulant therapy by continuous heparin-antithrombin III infusion in newborns with disseminated intravascular coagulation

In ten newborns with severe alteration of the coagulation system due to DIC, AT III concentrate was infused continuously after prior activation with heparin. The rise in AT III activity showed a great variability among the infants and for one child during the course of the therapy. The mean rise of AT III activity by 40 U/kg per day heparin was 8.7%. If AT III concentrate (40 U/kg per day) was activated with 200 U/kg per day heparin, excessive anticoagulation effect was only observed in one child. In four children who had failed to respond to prior heparin therapy, improvement of the coagulation status was achieved within 2 days.