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The coagulation system is not fully developed at birth and matures during the first months of infancy, complicating clinical decision making within hemostasis. This study evaluates coagulation parameters at birth and two months after birth, and tests whether cord blood can be used as a proxy for neonatal venous blood measurements. The Copenhagen Baby Heart Study (CBHS) and the COMPARE study comprise 13,237 cord blood samples and 444 parallel neonatal venous blood samples, with a two month follow-up in 362 children. Because coagulation parameters differed according to gestational age (GA), all analyses were stratified by GA. For neonatal venous blood, reference intervals for activated partial thromboplastin time (APTT) and prothrombin time (PT) were 28–43 s and 33–61% for GA 37–39 and 24–38 s and 30–65% for GA 40–42. Reference intervals for international normalized ratio (INR) and thrombocyte count were 1.1–1.7 and 194–409 × 109/L for GA 37–39 and 1.2–1.8 and 188–433 × 109/L for GA 40–42. Correlation coefficients between umbilical cord and neonatal venous blood for APTT, PT, INR, and thrombocyte count were 0.68, 0.72, 0.69, and 0.77 respectively, and the distributions of the parameters did not differ between the two types of blood (all p-values>0.05). This study describes new GA dependent reference intervals for common coagulation parameters in newborns and suggests that cord blood may serve as a proxy for neonatal venous blood for these traits. Such data will likely improve clinical decision making within hemostasis among newborn and infant children. [ABSTRACT FROM AUTHOR]