Bacterial Vaginosis in Pregnancy and the Risk of Prematurity A Meta-Analysis

,

Original Research

Bacterial Vaginosis in Pregnancy and the Risk of Prematurity A Meta-Analysis

J Fam Pract. 1999 November;48(11):885-892

By

Cheryl A. Flynn, MD, MS

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OBJECTIVE: We conducted this meta-analysis to determine the magnitude of the risk conferred by bacterial vaginosis during pregnancy on premature delivery.

SEARCH STRATEGY: We selected articles from a combination of the results of a MEDLINE search (1966-1996), a manual search of bibliographies, and contact with leading researchers.

SELECTION CRITERIA: We included case control and cohort studies evaluating the risk of preterm delivery, low birth weight, preterm premature rupture of membranes, or preterm labor for pregnant women who had bacterial vaginosis and those who did not.

DATA COLLECTION AND ANALYSIS: Two investigators independently conducted literature searches, applied inclusion criteria, performed data extraction, and critically appraised included studies. Summary estimates of risk were calculated as odds ratios (ORs) using the fixed and random effects models.

MAIN RESULTS: We included 19 studies in the final analysis. Bacterial vaginosis during pregnancy was associated with a statistically significant increased risk for all outcomes evaluated. The summary OR was 1.85 for preterm delivery (95% confidence interval [CI], 1.62-2.11), 1.57 for low birth weight (95% CI, 1.32-1.87), 1.83 for preterm premature rupture of membranes (95% CI, 1.39-2.44), and 2.19 for preterm labor (95% CI, 1.73-2.76). In the subanalyses for preterm delivery, bacterial vaginosis remained a significant risk factor. Pooling adjusted ORs yielded a 60% increased risk of preterm delivery given the presence of bacterial vaginosis.

CONCLUSION: Bacterial vaginosis is an important risk factor for prematurity and pregnancy morbidity. Further study will help clarify the benefits of treating bacterial vaginosis and the potential role of screening during pregnancy.

CLINICAL QUESTION
What is the association between bacterial vaginosis and preterm delivery?

Prematurity, whether defined by gestational age or birth weight, increases the risk of neonatal morbidity and mortality, as well as early childhood morbidity. Preterm birth, defined as delivery before 37 weeks’ gestation, accounts for 8% to 10% of all births¹ and leads to nearly 75% of all neonatal mortality and 50% of all long-term neurologic damage in children.² On average, first-year medical costs for infants born weighing less than 2500 grams exceed that of a full-term infant by $15,000.³

Between 25% and 60% of preterm births are thought to be attributable to maternal infections,^4,5 and are thus considered preventable. Bacterial vaginosis (BV) has been suggested as one potentially treatable risk factor for preterm delivery. BV is fairly common, with a prevalence ranging from 10% to 30% in an typical obstetrical population⁶ to more than 50% in some high-risk groups.⁷

Although otherwise thought to be a fairly benign condition, in pregnancy BV is estimated to confer a two- to threefold increased risk of prematurity.^4,8 Yet the relative risks from the literature range from^09,10> to 6.9.¹¹ These variations may be attributable to differences in study design, sample size, or confounders. The purpose of our meta-analysis was to estimate the magnitude of risk that BV poses on prematurity and pregnancy complications that may lead to prematurity.

Methods

Data Sources

To identify potential studies for inclusion, 2 independent investigators (CF and AH) conducted a MEDLINE search (1966-1996), using the terms “bacterial vaginosis,” “gardnerella” and “prematurity,” “labor-premature onset, ” “rupture of membranes-premature,” “preterm delivery,” or “preterm infant” as both medical subject headings and text words. The bibliographies of obstetric texts, all included studies, relevant reviews, and the Cochrane Library were also reviewed. Finally, we contacted several authors who had published articles on the subject in an attempt to identify any unpublished data.

Study Selection

Studies were included if they met the following criteria: (1) the population studied was pregnant women; (2) the risk factor considered was the presence of BV; (3) the outcomes measured included either gestational age or birth weight; secondary outcomes considered were preterm premature rupture of membranes and preterm onset of labor; and (4) study design was either case control or cohort trial evaluating the benefit of treating BV in pregnancy. Trials were included if sufficient data were available to compare the outcomes of those women who had BV with those who did not in the control cohort. Inclusion criteria were applied independently by the 2 investigators; differences were settled by consensus.

Non-English language papers and those containing duplication of previous data were excluded. For articles in which the data presentation prohibited the linking of BV to the outcomes of interest, we contacted the authors in writing for the original data. If the original data were unavailable, we excluded the study from final analysis.

Data Extraction

The 2 investigators also independently performed data extraction. Disagreements were settled by discussion and consensus.

The population data we collected included country, medical setting, and baseline risk of prematurity. We recorded inclusion and exclusion criteria, but those factors were insufficient to categorize the study population as either high, normal, or low risk. Therefore, baseline risk was determined by calculating the incidence of preterm delivery in the control group for each study. Since the standard incidence of preterm delivery is 8% to 10%, we considered as high risk those studies with rates greater than 10% in the non-BV group; those below were categorized as low or normal risk.