Preterm neonates display longer bleeding times compared to term infants, contributing to such complications as intraventricular hemorrhage (IVH), but little solid research has existed on differences in platelet functionality between these infants. Study findings published in Research & Practice in Thrombosis & Homeostasis provide information about preterm neonatal platelets, suggesting that their functionality is poorer at birth compared to full-term infants and does not return to normal levels during the first several weeks of life.
As care interventions have improved for the youngest preterm neonates, an increasing number have been born with complications related to prematurity, including IVH. The etiology of IVH is probably multifactorial; although it often occurs in the context of thrombocytopenia, which occurs in up to 70% of preterm neonates, platelet count alone does not accurately predict IVH risk. Some have postulated that poor platelet functionality in these infants might play a role in increased bleeding risk.
A team of researchers led by Nadia Thrane Hovgesen, MS, of Aarhus University Hospital in Denmark, studied this question in 43 preterm neonates and 21 term infants. Unlike most previous studies, the researchers used peripheral blood as opposed to umbilical blood. Although umbilical blood is easier to obtain, the authors noted that it may not adequately reflect true platelet functionality. Samples were obtained from the infants within the first 24 hours of life; additional samples were obtained when the preterm infants achieved what would have been their full gestational age (median = 7.1 weeks after birth).
The team assessed platelet numbers as well as platelet function, both in terms of aggregation and activation. To assess aggregation, investigators used whole blood impedance aggregometry, which measures the change in electrical impedance between two electrodes after blood has been exposed to an aggregation agonist. They also used flow cytometry – after exposing the cells to an activating trigger – to see whether the platelets expressed substances on their membrane relevant to platelet activation (e.g., platelet surface glycoprotein receptors) and whether they bound substances such as fibrinogen.
As expected, preterm infants had significantly lower median platelet counts at birth compared to infants born at term. Platelet aggregation did not differ between preterm and full-term infants at birth; however, platelet activation was comparatively reduced in preterm neonates compared to those born at term. For example, in the preterm neonate group, a significantly lower percentage of platelets were bound to fibrinogen after exposure to an activating agonist.
“Our finding of overall reduced levels of activation-dependent surface markers in preterm platelets at birth compared with term platelets is supported by several previous studies,” the authors noted.
However, little previous research has examined postnatal changes in infants who were born prematurely, and the existing results had been inconsistent. By the time these preterm neonates reached their expected term age, platelet activation had improved. Nevertheless, platelet activation had not yet reached the levels of term neonates; their platelet activation remained impaired, although overall platelet count and platelet aggregation values were not.
Further studies are needed to evaluate the potential clinical implications of this work. The authors noted despite their findings that preterm neonatal platelets still show impaired activation once infants reach their expected gestational age, such infants do not have an increased bleeding tendency. So, potential clinical implications for such patients are unclear.
Additionally, it’s unclear what these findings might mean clinically for preterm newborns.
The authors noted that because of study design limitations and the small sample size, the study could not examine potential associations between decreased platelet function and bleeding tendency, either generally or in the context of issues such as IVH. They added, “Further studies are needed to investigate if the reduced platelet activation contributes to the risk of bleeding and IVH in very preterm neonates.”
Any conflicts of interest declared by the authors can be found in the original article.
Reference
Hovgesen NT, Hviid CVB, Grevsen AK, Hansen AK, Hvas AM. Reduced platelet function in preterm neonates compared with term neonates. Res Pract Thromb Haemost. 2022;6(5):e12751.
