Matteo Bruschettini, Olga Romantsik, Simona Zappettini, Rita Banzi, Luca Antonio Ramenghi, Maria Grazia Calevo

Preterm birth remains the major risk factor for the development of intraventricular hemorrhage, an injury that occurs in 25% of very low birth weight infants. Intraventricular hemorrhage is thought to be venous in origin and intrinsic thromboses in the germinal matrix are likely to play a triggering role. Antithrombin, a glycoprotein synthesized in the liver, is the major plasma inhibitor of thrombin thus modulating blood coagulation. Very low birth weight newborn infants have low levels of antithrombin and the risk of developing intraventricular hemorrhage is increased by the presence of hypercoagulability in the first hours of life. The administration of anticoagulants such as antithrombin may offset the increased risk of developing intraventricular hemorrhage. Anticoagulants may also reduce the risk of developing parenchymal venous infarct, a condition known to complicate intraventricular hemorrhage. To assess whether the prophylactic administration of antithrombin (started within the first 24 hours after birth) reduces the incidence of germinal matrix-intraventricular hemorrhage in very preterm neonates when compared to placebo, no treatment, or heparin. We searched the Cochrane Central Register of Controlled Trials (The Cochrane Library 2015), MEDLINE (1996 to 22 November 2015), EMBASE (1980 to 22 November 2015), and CINAHL (1982 to 22 November 2015). No language restrictions were applied. We searched the abstracts of the major congresses in the field (Perinatal Society of Australia and New Zealand and Pediatric Academic Societies) from 2000 to 2015. Randomised controlled trials, quasi-randomised controlled trials and cluster trials comparing the administration of early, i.e. within the first 24 hours of life, antithrombin in very preterm infants (gestational age < 32 weeks, any birth weight). For each of the included trials, two authors independently extracted data (e.g. number of participants, birth weight, gestational age, antithrombin formulation (plasma-derived or recombinant), mode of administration, and duration of therapy, etc.) and assessed the risk of bias (e.g. adequacy of randomization, blinding, completeness of follow-up). The primary outcomes considered in this review are intraventricular hemorrhage and severe intraventricular hemorrhage. Two randomized controlled trials, for a total of 182 infants, met the inclusion criteria of this review. Both trials compared antithrombin with placebo. We found no significant differences in the rates of intraventricular hemorrhage (typical RR 1.30, CI 95% 0.87 to 1.93, typical RD 0.09, 95% CI -0.05 to 0.23; 2 studies, 175 infants; I² = 18% for RR and I² = 42% for RD) and severe intraventricular hemorrhage (typical RR 1.04, CI 95% 0.55 to 1.94; typical RD 0.01, 95% CI -0.11 to 0.12; 2 studies, 175 infants; I² = 0% for RR and I² = 0% for RD). Among secondary outcomes, we found no significant differences in terms of neonatal mortality (typical RR 2.00, CI 95% 0.62 to 6.45; typical RD 0.04, 95% CI -0.03 to 0.12; 2 studies, 182 infants; I² = 46% for RR and I² = 61% for RD) and in the other specified outcomes, such as bronchopulmonary dysplasia. The quality of the evidence supporting these findings is limited due to the imprecision of the estimates. The administration of antithrombin seems not to reduce the incidence and severity of intraventricular hemorrhage in very preterm infants. Limited evidence is available on other clinically relevant outcomes. Given the imprecision of the estimate, the results of this systematic review are consistent with either a benefit or a detrimental effect of antithrombin and do not provide a definitive answer to the review question.