Table 1. Examples of hemostasis related changes according to stage of development.

Secondary hemostasis	Platelet function	von Willebrand factor	Other blood components
Neonates	Preterm infants	Neonates	Hematocrit
Concentration of vitamin K dependent coagulation factors (II, VII, IX, X, protein C, protein S), antithrombin, thrombin generation and clot lysis reduced compared with older children	Reduced platelet aggregation and platelet hyporeactivity	High to normal levels that become similar to adults within approximately 6 months of life	Extremely high at birth and then gradually decreasing in the following months
	Decreased platelet adhesion compared with term infants (not due to VWF)
	Longer bleeding times in very low birth weight infants
Childhood to adulthood	Term neonates: paradoxical findings	Adults	Platelet count
Antithrombin reaches that of adults after around 6 months	Relative reduction in platelet function, decreased expression of platelet activation markers, and less responsive platelets compared to adults in some studies, but bleeding time and PFA closure times shorter than in adults	Levels increase with age (~1–2% increase per year)	Does not change appreciably throughout life
Proteins C and S increase throughout childhood, but levels do not reach those of adults until adolescence	Potentially attributable to higher levels of hematocrit and VWF in neonates, thereby ‘re-balancing’ neonatal hemostasis		D-dimer
	Childhood to adulthood		Levels increase with age, especially after 50
	Platelet hypo-reactivity is still present 3–4 days after birth, both in term and in preterm infants, but is similar to adults by age of one

PFA, Platelet function Analyzer; VWF, von Willebrand factor. Largely summarized from cited references.