Heparin therapy for complications of placental dysfunction: A systematic review of the literature

Objective. To assess the benefits and harms of antenatal antithrombotic therapy for women at risk of adverse pregnancy outcomes associated with placental dysfunction. Search strategy. PUBMED and the Cochrane Controlled Trials Register (CENTRAL) were searched. Reference lists of retrieved studies were searched by hand. No date or language restrictions were placed. Date of last search February 2008. Selection criteria. Randomized controlled trials comparing antenatal antithrombotic therapy (alone or combined with other agents) with placebo or no treatment were considered. Cohort studies with an appropriate control group were also considered. Studies were evaluated independently for appropriateness for inclusion and methodological quality without consideration of their results. Our search strategy identified five case series, two cohort studies with a control group, and one randomized controlled trial. All of the case series and one of the cohort studies were excluded. Data collection and analysis. The methodological quality of the included studies was poor. There was considerable variation in methodology and the interventions. It was not appropriate to combine results in meta‐analysis. Main results. From the randomized trial, heparin was not associated with a reduction in preterm birth less than 37 weeks gestation (Heparin 5/68 versus Control 7/39; relative risk (RR) 0.41; 95% confidence intervals (CIs) 0.14–1.20), or birth weight below 10th centile (Heparin 4/68 versus Control 6/39; RR 0.38; 95% CI 0.11–1.27). Conclusion. There is insufficient information to recommend the use of heparin during pregnancy for women at risk of complications due to placental dysfunction. Further information from randomized trials is required.