Abstract

Preterm birth is a significant public health problem worldwide, leading to substantial mortality in the newborn period, and a considerable burden of complications longer term, for affected infants and their carers. The fact that it is so common, and rates vary between different populations, raising the question of whether in some circumstances it might be an adaptive trait. In this review, we outline some of the evolutionary explanations put forward for preterm birth. We specifically address the hypothesis of the predictive adaptive response, setting it in the context of the Developmental Origins of Health and Disease, and explore the predictions that this hypothesis makes for the potential causes and consequences of preterm birth. We describe how preterm birth can be triggered by a range of adverse environmental factors, including nutrition, stress and relative socioeconomic status. Examining the literature for any associated longer-term phenotypic changes, we find no strong evidence for a marked temporal shift in the reproductive life-history trajectory, but more persuasive evidence for a re-programming of the cardiovascular and endocrine system, and a range of effects on neurodevelopment. Distinguishing between preterm birth as a predictive, rather than immediate adaptive response will depend on the demonstration of a positive effect of these alterations in developmental trajectories on reproductive fitness.This article is part of the theme issue ‘Developing differences: early-life effects and evolutionary medicine'.

Highlights

  • Prematurity [1] affects 11% of live births worldwide

  • The null hypothesis for preterm birth having any adaptive significance is that it represents a pathophysiological response to triggers such as systemic or intra-uterine infections, or the endothelial dysfunction associated with diseases such as pre-eclampsia

  • A final possibility, which we examine in detail in this 2 paper, is that preterm birth may form one of a suite of predictive adaptive responses (PAR) to an adverse environment: the information provided by the maternal niche to the fetus about the ex utero environment leads to changes in developmental trajectories appropriate to this environment

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Summary

Introduction

Prematurity (delivery at a gestational age of less than 37 weeks) [1] affects 11% of live births worldwide. The sequelae of preterm birth constitute a significant public health problem, with preterm birth complications responsible for 35% of neonatal deaths (in the first 28 days of life) worldwide [2], and contributing to 50% of all deaths in this age group. In addition to death in the neonatal period, preterm birth is associated with a range of longer-term physical and neurodevelopmental consequences such as moderate/severe cognitive impairment, motor impairment and cerebral palsy [2]. It leads to an estimated annual 106 million disability-adjusted life years [3], and places a significant burden on parents, carers and health systems [4]. We conclude by examining the limitations of the data, and ask whether prematurity should be best seen as an immediate, or predictive, adaptive response

Could preterm birth represent an adaptive response to adverse conditions?
The PAR hypothesis
Predictions for preterm birth as part of a PAR
Preterm birth and low birth weight
Preterm birth as a response to adverse life conditions
Preterm birth and reproductive life histories
Preterm birth and long-term phenotypic changes
10. Limitations of the evidence
12. Conclusion and public health implications
34. Carlo WA et al 2010 High mortality rates for very
63. Piyasena C et al 2016 Dynamic changes in DNA
Findings
40. Shaw GM et al 2014 Maternal prepregnancy body
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