What coagulation factors are low at birth?

From the Guidelines

At birth, several coagulation factors are physiologically low in newborns, including vitamin K-dependent factors (II, VII, IX, and X), which are decreased to levels comparable to those achieved in adults receiving therapeutic amounts of vitamin K antagonists with target international normalized ratios (INRs) of 2.0 to 3.0 1. These factors are essential for blood coagulation, and their low levels contribute to the delicate balance of the coagulation system in newborns, known as "developmental hemostasis" 1. The coagulation factors that are low at birth include:

• Vitamin K-dependent factors: II, VII, IX, and X
• Contact factors: XI, XII
• Factors V and VIII These low levels are more pronounced in premature infants and can increase the risk of bleeding disorders if not properly managed 1. Vitamin K administration is standard practice after birth to support the synthesis of these coagulation factors and prevent vitamin K deficiency bleeding 1. The levels of these factors gradually increase over the first weeks to months of life as the liver matures and vitamin K stores accumulate 1. Understanding these normal variations in coagulation factors is essential for properly interpreting coagulation tests in neonates and distinguishing between physiologic findings and pathologic bleeding disorders 1.

From the Research

Coagulation Factors Low at Birth

• The coagulation factors that are low at birth include:
  • Vitamin K-dependent factors: II, VII, IX, X 2, 3, 4
  • Contact factors: XI and XII are reduced to about 50% of normal adult values 3
  • Fibrinogen, factor XIII are decreased 4
  • Plasma concentrations of naturally occurring anticoagulant proteins: antithrombin, protein C, and protein S are significantly lower at birth than during adult years 3
  • Plasminogen is reduced by approximately 50% 3
• These low levels of coagulation factors can lead to an increased risk of bleeding in newborns, particularly vitamin K deficiency bleeding (VKDB) 2, 3

Reference Ranges for Coagulation Factors in Newborns

• A study established reference ranges for coagulation factors in healthy newborns, including:
  • Activated partial thromboplastin time (aPTT): 28.6-46.2 s
  • Prothrombin time (PT): 71.3-110.6 s
  • Fibrinogen: 1.2-3.2 g/L
  • Factor II: 51.0-130.0 U/dL
  • Factor V: 68.0-233.0 U/dL
  • Factor VIII: 45.0-152.0 U/dL
  • Factor IX: 32.0-96.0 U/dL
  • Factor XI: 29.0-112.0 U/dL 5