Objective We determined thromboelastographic (TEG) profiles of healthy very low birthweight infants (VLBWIs) of the day of birth and at set intervals during their first month.

Design Prospective observational study with blinded clinical and laboratory follow-up.

Setting Level III neonatal intensive care unit (June 2015 to June 2018).

Patients Consecutive qualifying VLBWIs were enrolled at birth and followed up for 30 days.

Interventions and main outcomes measures Laboratory (citrated-native TEG, prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinogen, blood count) and clinical variables were retrieved at birth, 3rd–5th, 10th and 30th day of life. Blood samples temporally related to events with a potential hemostatic impact (sepsis, bleeding, platelets/plasma transfusions, ibuprofen/indomethacin administration) were excluded from analysis.

Results We enrolled 201 VLBWIs and 72 full-term neonates. Sixty-seven of the healthy VLBWIs completed the 30-day follow-up. 541 TEG traces were analysed.

On day 1, the median (minimum–maximum) TEG values were as follows: reaction time (R), 8.2 min (1–21.8); kinetics (K), 2.8 min (0.8–16); α angle, 51° (14.2–80.6); maximum amplitude (MA), 54.9 mm (23.9–76.8). PT and APTT were 15.9 s (11.7–51.2) and 59 s (37.8–97.5), respectively. The above parameters suggest minor hypocoagulability compared with term infants. On day 30, the median (minimum–maximum) R was 5 (1–16.9), K 1 (0.8–4.1), α 74.7 (41.1–86.7) and MA 70.2 (35.8–79.7). PT and APTT were 12.1 (10.4–16.6) and 38.8 (29.6–51.4), respectively. Those parameters are consistent with a relatively hypercoagulable phenotype, compared with term infants.

Conclusions Healthy VLBWIs have a prolonged PT and APTT, but their TEG profiles suggest a relatively balanced hemostatic system, with slight hypocoagulability initially (compared with term neonates), gradually evolving to a somewhat more procoagulant phenotype over the first month.