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Meta-Analysis
. 2011 Jun;24(6):778-86.
doi: 10.3109/14767058.2010.530707. Epub 2010 Dec 10.

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

David N Hackney  1 , J Christopher Glantz
Affiliations
Meta-Analysis

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

David N Hackney et al. J Matern Fetal Neonatal Med. 2011 Jun.

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 I(2) 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 (I(2) = 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.

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Figures

Figure 1
Figure 1
Search strategy
Figure 2
Figure 2
Forest Plot of studies of preterm birth after vaginal bleeding. The y-axis is Log (Odds Ratio). Individual studies are demonstrated graphically with 95% confidence intervals.
Figure 3
Figure 3
Funnel Plot of studies of preterm birth after vaginal bleeding. The y-axis is Log (Odds Ratio) and the x-axis is standard error of the Log (Odds Ratio).
Figure 4
Figure 4
Stratified forest plot of cohort studies of preterm birth after vaginal bleeding stratified according to study design. The y-axis is Log (Odds Ratio). Individual studies are demonstrated graphically with 95% confidence intervals.
Figure 5
Figure 5
Scatter plot of the incidence of vaginal bleeding within cohort studies and the Log (Odds Ratio) of preterm birth. Black circles represent individual studies with a diameter that is proportional to their sample size. Only studies that used a population sample were included.
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