BACKGROUND: Nosocomial infections continue to be a significant cause of morbidity and mortality among preterm and/or low birth weight infants. Maternal transport of immunoglobulins to the fetus mainly occurs after 32 weeks gestation and endogenous synthesis does not begin until several months after birth. Administration of intravenous immunoglobulin provides IgG that can bind to cell surface receptors, provide opsonic activity, activate complement, promote antibody dependent cytotoxicity, and improve neutrophilic chemo luminescence. Intravenous immunoglobulin thus has the potential of preventing or altering the course of nosocomial infections. OBJECTIVES: To assess the effectiveness/safety of intravenous immunoglobulin (IVIG) administration (compared to placebo or no intervention) to preterm (< 37 weeks gestational age at birth) and/or low birth weight (LBW) (< 2500 g BW) infants in preventing nosocomial infections. SEARCH STRATEGY: MEDLINE, EMBASE, and The Cochrane Library Databases were searched in September 2003 using the keywords: immunoglobulin and infant-newborn and random allocation or controlled trial or randomized controlled trial (RCT). The reference lists of identified RCTs and personal files were searched. No language restrictions were applied. SELECTION CRITERIA: The criteria used to select studies for inclusion in this overview were: 1) DESIGN: RCTs in which administration of IVIG was compared to a control group that received a placebo or no intervention. 2) POPULATION: preterm (< 37 weeks gestational age) and/or LBW (<2500 g) infants. 3) INTERVENTION: IVIG for the prevention of bacterial/fungal infection during initial hospital stay (8 days or longer). (Studies that were primarily designed to assess the effect of IVIG on humoral immune markers were excluded as were studies in which the follow-up period was one week or less).4) At least one of the following outcomes was reported: sepsis, any serious infection, death from all causes, death from infection, length of hospital stay, intraventricular hemorrhage (IVH), necrotizing enterocolitis (NEC), bronchopulmonary dysplasia (BPD). DATA COLLECTION AND ANALYSIS: Two reviewers independently abstracted information for each outcome reported in each study, and one researcher (AO) checked for any discrepancies and pooled the results. Relative risk (RR) and Risk Difference (RD) with 95% confidence intervals (CI) using the fixed effects model are reported. When a statistically significant RD was found the number needed to treat (NNT) was also calculated with 95% CIs. The results include all accepted studies in which the outcome of interest was reported. Statistically significant between study heterogeneity was reported. The results of the inconsistency test (I squared) are also reported when statistically significant heterogeneity was found. MAIN RESULTS: No new trials were identified in September 2003. Nineteen studies met inclusion criteria. These included approximately 5,000 preterm and/or LBW infants and reported on at least one of the outcomes of interest for this systematic review. When all studies were combined there was a statistically significant reduction (p = 0.02) in sepsis, RR [0.85 (95% CI 0.74, 0.98)] and RD [-0.03 (95% CI 0.00, -0.05)], NNT 33. There was statistically significant between-study heterogeneity (p = 0.02); I squared 54%. A statistically significant reduction was found for any serious infection, one or more episodes, when all studies were combined [RR 0.82 (95% CI 0.74, 0.92); RD -0.04 (95% CI -0.02, -0.06,); NNT 25 (95% CI, 16.7, 50). There was statistically significant between-study heterogeneity (p = 0.0006); I squared 50%. There were no statistically significant differences for mortality from all causes, mortality from infection, incidence of NEC, BPD and IVH or length of hospital stay. No major adverse effects of IVIG were reported in any of the studies. REVIEWER'S CONCLUSIONS: IVIG administration results in a 3% reduction in sepsis and a 4% reduction in any serious infection, one or more episodes, but is not associated with reductions in other important outcomes: sepsis, NEC, IVH, or length of hospital stay. Most importantly, IVIG administration does not have any significant effect on mortality from any cause or from infections. Prophylactic use of IVIG is not associated with any short term serious side effects. From a clinical perspective a 3-4% reduction in nosocomial infections without a reduction in mortality or other important clinical outcomes is of marginal importance.The decision to use prophylactic IVIG will depend on the costs and the values assigned to the clinical outcomes. There is no justification for further RCTs testing the efficacy of previously studied IVIG preparations to reduce nosocomial infections in preterm and/or LBW infants. The results of these meta-analyses should encourage basic scientists and clinicians to pursue other avenues to prevent nosocomial infections.