Study	Reason for exclusion
Costakos 2003	Costakos 2003 studied infants 22 to 32 weeks' gestational age born to mothers who wished to breast feed. Group 1 received 1 mg of vitamin K and Group 2 received 0.5 mg of vitamin K. During the time period of the study 81 infants of 22 to 32 weeks' gestation were admitted to the NICU. Treatment assignment was based on physician choice (non‐random assignment). The more immature and lowest birth weight infants tended to get the lower dose of vitamin K.
Kumar 2001	Kumar 2001 assessed vitamin K status in preterm infants (≤ 36 weeks' gestation) by measuring plasma vitamin K and plasma protein‐induced in vitamin K absence (PIVKA II) from birth until 40 weeks' postconceptional age. Preterm infants were divided at birth into groups by gestational age (group 1, ≤ 28 weeks; group 2, 29 to 32 weeks; group 3, 33 to 36 weeks). Supplemental vitamin K (1 mg IM) was administered at birth followed by 60 µg/day (weight < 1000 g) or 130 µg/day (weight ≥ 1000 g) via total parenteral nutrition. After hyperalimentation, most received vitamin K‐fortified enteral feedings with the remainder receiving unfortified breast milk. Blood was obtained for PIVKA II in cord blood and for PIVKA II and vitamin K at 2 weeks and 6 weeks after birth and at 40 weeks postconception.
Ogata 1988	Ogata 1988 measured Factor II coagulant antigen (FII‐AG), the protein induced by vitamin K absence or antagonist II (PIVKA‐II), and coagulant activity (Normotest) in low birth weight infants. Infants whose Normotest levels were less than 30% at 1 day (group A) received vitamin K2, and the others whose Normotest levels were greater than 30% at 1 day (group B) were not treated.
Rossi 1996	Rossi 1996 studied infants that were 27 to 42 weeks' gestation at birth. The population included preterm infants and high risk term infants (unclear what deemed the term infants high risk). Non‐randomized report of biochemical markers after recommended dosing changes in preterm infants.
Seydewitz 1984	Seydewitz 1984 studied infants that were preterm or small‐for‐date, or both. Data on only the preterm infants included in the study were unavailable. Infants were randomized into 2 groups: 1 group received 1 mg IM vitamin K after a first plasma sample was obtained; the second group received 1 mg IM vitamin K after a second plasma sample was obtained (time between the first sampling and second sampling was 4 hours in 1 series and 24 hours in another series).
Vakrilova 1995	Vakrilova 1995 conducted a prospective study of newborn infants with birth weight below 2500 g comparing the effect of IM vitamin K to oral vitamin K for preventing hemorrhagic disease of the newborn. Additional comparison group included healthy term infants who had not received vitamin K. Treatment assignment unclear.

Abbreviations: IM: intramuscular; PIVKA: plasma protein‐induced in vitamin K absence.