The effect of combined antenatal vitamin K and phenobarbital therapy on umbilical
blood coagulation studies in infants less than 34 weeks' gestation.
Author(s): Thorp JA, Caspers DR, Cohen GR, Zucker ML, Strope BD, McKenzie DR.
Affiliation(s): Department of Obstetrics and Gynecology, Saint Luke's Hospital of Kansas City,
Missouri, USA.
Publication date & source: 1995, Obstet Gynecol. , 86(6):982-9
OBJECTIVE: To determine if antenatal vitamin K and phenobarbital therapy affect
coagulation studies in umbilical blood at birth, and to provide 95% reference
ranges for umbilical blood coagulation parameters in premature gestations.
METHODS: Patients at imminent risk for spontaneous 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), functional coagulation factors, and decarboxylated
prothrombin assays were performed on umbilical blood specimens. Decarboxylated
prothrombin, also known as "protein induced by vitamin K absence-factor II" or
precursor prothrombin, is a sensitive marker for vitamin K deficiency.
Standardized values of PT and PTT are reported in seconds and standardized values
of factor assays in percentage of normal adult functional activity (mean +/- one
standard deviation).
RESULTS: Newborns in the placebo 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 versus 42.0
+/- 12.1%), factor VII (67.0 +/- 20.9 versus 66.8 +/- 18.9%), factor 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 about half as likely as those in the placebo
group to have detectable decarboxylated 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 phenobarbital 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 presence of decarboxylated prothrombin in
umbilical blood at birth. There is significant improvement in umbilical blood
coagulation tests as gestational age advances from 24 to 34 weeks.
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