THE EFFECT OF COMBINED ANTENATAL VITAMIN-K AND PHENOBARBITAL THERAPY ON UMBILICAL BLOOD-COAGULATION STUDIES IN INFANTS LESS-THAN 34 WEEKS GESTATION

Objective: To determine if antenatal vitamin K and phenobarbital thera py affect coagulation studies in umbilical blood at birth, and to prov ide 95% reference ranges for umbilical blood coagulation parameters in premature gestations. Methods: Patients at imminent risk for spontane ous or indicated premature delivery less than 34 weeks' gestation were randomized to receive either placebo or vitamin K and phenobarbital. Prothrombin time (PT), activated partial thromboplastin time (PTT), fu nctional coagulation factors, and decarboxylated prothrombin assays we re performed on umbilical blood specimens. Decarboxylated prothrombin, also known as ''protein induced by vitamin K absence-factor II'' or p recursor prothrombin, is a sensitive marker for vitamin K deficiency. Standardized values of PT and PTT are reported in seconds and standard ized values of factor assays in percentage of normal adult functional activity (mean +/- one standard deviation). Results: Newborns in the p lacebo and treatment groups had similar umbilical blood PT (12.6 +/- 1 .2 versus 12.7 +/- 1.4 seconds), PTT (48.8 +/- 13.4 versus 49.6 +/- 13 .8 seconds), and functional activity of factor II (40.3 +/- 12.5 versu s 42.0 +/- 12.1%), factor VII (67.0 +/- 20.9 versus 66.8 +/- 18.9%), f actor IX (27.4 +/- 12.8 versus 25.8 +/- 8.9%), and factor X (47.0 +/- 12.8 versus 49.2 +/- 11.6%). Newborns in the treatment group were abou t half as likely as those in the placebo group to have detectable deca rboxylated prothrombin levels in umbilical blood at birth (gestational age-adjusted odds ratio 0.47, 95% confidence interval 0.22-1.01; P = .05). Conclusions: Combined maternal therapy with vitamin K and phenob arbital before premature delivery does not affect umbilical blood PT, PTT, or functional activity of vitamin K-dependent coagulation factors II, VII, IX, and X. However, it is associated with the reduced presen ce of decarboxylated prothrombin in umbilical blood at birth. There is significant improvement in umbilical blood coagulation tests as gesta tional age advances from 24 to 34 weeks.