Vaginal bleeding in early pregnancy and preterm birth: systemic review and analysis of heterogeneity

Abstract

Objective. To systemically review published studies of vaginal bleeding and the risk of preterm birth (PTB) and explore sources of heterogeneity between them.

Methods. The literature was searched for peer-reviewed articles from 1980 to 2009 in which the primary analysis was the risk of PTB among low-risk subjects with and without bleeding. Heterogeneity was assessed through I² statistics, and sources of heterogeneity were explored through subgroup analyses and meta-regression.

Results. 218 studies were initially identified, 64 reviewed and 23 included. The pooled Odds Ratio for PTB was 1.74, though significant heterogeneity was present (I² = 49.7%). Meta-regression demonstrated a significant association between a study's incidence of bleeding and quality assessment and subsequent odds ratio, such that studies with a lower quality assessment or lower incidence of bleeding demonstrated an increased odds of PTB.

Conclusions. Bleeding in early pregnancy is associated with an increased risk of PTB; however, excessive heterogeneity exists among published studies. The heterogeneity arises in part from differences in the reported incidence of bleeding within study populations. Presumably studies that identify bleeding in a larger percentage of subjects consequently dilute the magnitude of the risk.

Keywords:

• Vaginal bleeding
• preterm birth
• metaanalysis
• metaregression
• systemic review
• threatened abortion
• preterm premature rupture of membranes

Acknowledgements

We acknowledge reference librarian Margaret Chretien for her assistance with the development of the search strategy and Carol Lin, MD, for her assistance with the manuscript. Funding: Women's Reproductive Health Research K-12: HD001332-09.