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. 2012;7(7):e40228.
doi: 10.1371/journal.pone.0040228. Epub 2012 Jul 6.

The association of season and temperature with adverse pregnancy outcome in two German states, a time-series analysis

Jennyfer Wolf  1 , Ben Armstrong
Affiliations

The association of season and temperature with adverse pregnancy outcome in two German states, a time-series analysis

Jennyfer Wolf et al. PLoS One. 2012.

Abstract

Background: A seasonality of low birth weight (LBW) and preterm birth (PTB) has been described for most regions and there is evidence that this pattern is caused by ambient outdoor temperature. However, the association as such, the direction of effect and the critical time of exposure remain controversial.

Methods: Logistic, time-series regression was performed on nearly 300,000 births from two German states to study the association between season and daily mean temperature and changes in daily proportions of term LBW (tLBW) or PTB. Analyses were adjusted for time-varying factors. Temperature exposures were examined during different periods of pregnancy.

Results: Weak evidence for an association between season of conception, season of birth or ambient outdoor temperature and tLBW or PTB was found. Results of analyses of temperature were not consistent between the two states. Different sources of bias which would have artificially led to stronger findings were detected and are described.

Conclusions: No clear evidence for an association between season of conception, season of birth or temperature and tLBW or PTB was found. In the study of pregnancy outcome different sources of bias can be identified which can potentially explain heterogeneous findings of the past.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Seasonal pattern of PTB without and with pregnancies-at-risk approach.
Figure 2
Figure 2. PTB proportions with (left) and without (right) data restriction (pregnancies-at-risk approach).
See this image and copyright information in PMC

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