The Relationship Between Apparent Temperature and Daily Number of Live Births in Montreal
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BRIEF REPORTS
The Relationship Between Apparent Temperature and Daily Number of Live Births in Montreal Tarik Benmarhnia1 • Nathalie Auger2 • Virginie Stanislas2 • Ernest Lo2 Jay S. Kaufman3
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Ó Springer Science+Business Media New York 2015
Abstract Objectives Temperature is a hypothesized determinant of early delivery, but seasonal and long term trends, delayed effects of temperature, and the influence of extreme cold temperatures have not yet been addressed. We aim to study the influence of apparent temperature on daily number of births, considering lag structures, seasonality and long term trends. Methods We used daily number of births in conjunction with apparent outdoor temperatures between 1981 and 2010 in Montreal. We used Poisson regression combined with a distributed lag nonlinear model to consider nonlinear relationships between temperature and daily number of births across specific lag periods. Results We found that apparent temperature was associated with the daily number of births in Montreal, with a 1-day delay. We found an increase in births on hot days, and decrease on cold days, both offset by a harvesting effect after 4 and 5 days. Conclusions for Practice This study suggests that the number of births is affected by extreme temperatures. Obstetric and perinatal service providers should be prepared for spikes in the number of births caused by extreme temperatures.
& Tarik Benmarhnia [email protected] 1
Institute for Health and Social Policy, McGill University, Meredith, Charles, House, 1130 Pine Avenue West, Montreal, QC H3A 1A3, Canada
2
Institut National de Sante´ Publique du Que´bec, Montreal, QC, Canada
3
Department of Epidemiology, Biostatistics, and Occupational Health, McGill University, Montreal, QC, Canada
Keywords Apparent temperature Weather Obstetric and pediatric health planning Time series analysis
Significance Understanding these relationships could suggest environmental mechanisms for triggering labor, but may also be useful for planning of obstetric and pediatric health care services by anticipating potential birth spikes during temperature-related events.
Introduction Recently, there has been strong interest in assessing environmental conditions such as ambient temperature [1] as determinants of early delivery [2]. Some studies have suggested an association between heat and preterm birth (defined as babies born alive before 37 weeks of gestation) [3– 6]. Other studies assessed such association but they did not find any association [7, 8]. These studies have mainly focused on preterm births without considering the possibility that temperature could trigger labor early among term pregnancies (i.e. babies born after 37 weeks of pregnancy). Furthermore, substantial seasonal variation may exist in the daily number of births, which can produce apparent births spikes during temperature-related events. Temperature generally shows effects that are non-linear and delayed in time [9]. Yet, previous studies have not addressed seasonal and long term trends, delayed
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