Asthma diagnosis and treatment
Preterm delivery and asthma: A systematic review and meta-analysis

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Background

Accumulating evidence suggests that reduced duration of pregnancy predicts increased risk of asthma, but the studies published have been inconsistent.

Objective

We sought to synthesize the evidence on the relation between preterm delivery and the risk of asthma later in life and to assess differences between the studies as potential sources for heterogeneity of the results.

Methods

We conducted a MEDLINE search (until the end of May 2005). The outcome was asthma. The determinant of interest was preterm delivery defined as a gestational age of less than 37 weeks.

Results

We identified 19 articles that provided estimates for the meta-analysis. The summary effect estimates for asthma (fixed-effects odds ratio, 1.074 [95% CI, 1.072-1.075]; heterogeneity P = .000; random-effects odds ratio, 1.366 [95% CI, 1.303-1.432]) showed an increased risk in relation to preterm delivery, with substantial heterogeneity between study-specific estimates. The effect of preterm delivery on asthma was stronger in cross-sectional studies; studies with broad outcome criteria, a small sample size, and a younger study population; and studies conducted in English-speaking populations, outside Europe, and published more recently. In metaregression, adjusting for other determinants, the effect estimate was significantly associated only with the mean age of the study population.

Conclusions

The weight of evidence shows that preterm babies have an increased risk of asthma compared with term babies.

Clinical implications

Recognition of prematurity as a determinant of asthma emphasizes the importance of active treatment of physiologic airflow obstruction and a need for special preventive measures against known environmental determinants of asthma in preterm babies.

Section snippets

Search strategy and inclusion criteria

We performed a systematic literature search of the MEDLINE database from 1966 through May 2005 using the following search command: asthma [Epidemiology, Etiology, Genetics, Pathology] AND preterm delivery [Premature labor, Premature Infant, Gestational Age]. The abstracts identified by this search were screened to eliminate the obviously irrelevant ones. For the remaining, copies of the full articles were retrieved and screened according to the following a priori inclusion criteria: (1)

Studies

The MEDLINE search identified 62 articles. On the basis of their abstracts, 38 studies were eliminated as being obviously irrelevant. The remaining 24 studies were retrieved and reviewed in detail: 11 met the criteria defined in the “Methods” section and were included in the analysis. Reference lists of the articles that fulfilled our inclusion criteria were checked; 17 further articles were identified and reviewed, and 8 of these fulfilled our inclusion criteria and consequently were included

Discussion

This systematic review and meta-analysis based on 19 epidemiologic studies fulfilling a priori inclusion criteria indicates that children born prematurely have an approximately 7% higher risk of asthma compared with term children. The magnitude of the study-specific estimates varied substantially. Taking into account this heterogeneity, preterm babies could have, on average, a 36% higher risk of asthma than term babies.

In stratified analyses the effect of preterm delivery on asthma was stronger

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    Supported by the West Midlands Regional Levy Board, United Kingdom.

    Disclosure of potential conflict of interest: The authors have declared that they have no conflict of interest.

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