The relationship between apparent temperature and daily number of live births in Montreal

Benmarhnia, T, Auger N, Stanislas V, Lo E, Kaufman JS.  2015.  The relationship between apparent temperature and daily number of live births in Montreal. Maternal and Child Health Journal. 19:2548-2551.

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ambient air-pollution, apparent temperature, delivery, environmental-temperature, epidemiology, heat, maternal exposure, nonlinear models, obstetric and pediatric health planning, preterm birth, risk, time series analysis, time-series-analysis, weather


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.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 non-linear relationships between temperature and daily number of births across specific lag periods.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.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.