Maternally administered antenatal vitamin K1: effect on neonatal prothrombin activity, partial thromboplastin time, and intraventricular hemorrhage.

Infants weighing 1500 g or less at birth are susceptible to intraventricular hemorrhage. This may be due in part to low concentrations of vitamin K-dependent clotting factors. Women in labor between 24-34 weeks' gestation were selected, according to their hospital registration number, to receive 10 mg vitamin K1 intramuscularly at least four hours before delivery. Control women received no vitamin K. The study included only infants born of mothers who were in hospital more than four hours before delivery, who weighed 1500 g or less at birth, and were less than 34 weeks' gestation. Twenty vitamin K1 and 33 control infants qualified for the study. Infants in both groups received routine postnatal vitamin K1. On admission, the infant's prothrombin activity and partial thromboplastin time (PTT) were measured. A head ultrasound was done between days 2 and 4 of life. Results demonstrated significantly improved prothrombin activity, a nonsignificant trend toward improved PTT, and a significantly decreased frequency of intraventricular hemorrhage in infants whose mothers had received vitamin K1. The effect of antenatal vitamin K1 on prothrombin activity and PTT appeared to be more pronounced in female infants.