Extreme heat shortens the duration of pregnancy.

While in the coming years is forecast extreme conditions of heat, there is little available information on its possible effects on the duration of pregnancy ”, explains to SINC Payam Dadvand, expert at the Center for epidemiological research and environmental of Barcelona (CREAL).

Dadvand and his team the short-term impact of maternal exposure to environmental extreme temperatures during pregnancy in a sample of 7.585 births that took place during the period 2001-2005 in Barcelona. In addition, they used national data on the heat and the daily temperature for the period from 1983-2006.

The authors applied three indicators of extreme heat conditions based on exposure to an unusual heat and high humidity, and quantified change in the duration of pregnancy after maternal exposure to extreme heat conditions.

The results, published in the journal Environmental Health Perspectives, reveal that maternal exposure to an extreme heat can have an immediate effect on the duration of pregnancy – there is little evidence of an association beyond the date of delivery and the day before –, and that these extreme temperatures are associated with a reduction in the gestational ages of children.

maternal exposure to an extreme heat can affect the duration of pregnancy, according to the study. Image: Montse PB

although according to Dadvand, more studies are needed to confirm these results in different contexts, an episode of unusual heat the day before birth is associated with a reduction of an average day of pregnancy. These data could achieve a reduction of five days for more extreme values.

With weather forecasts, and taking into account that a reduction of up to a week in duration of pregnancy has been associated with adverse results for the health of the newborn infants, the authors argue that future studies should consider these factors to inform public health interventions appropriate.

The effects of heat

Pregnancy tends to make women more vulnerable to heat stress. Previous studies already viewing these extreme conditions with the induction of uterine contractions, an increase in the secretion of hormones related to childbirth (oxytocin and prostaglandins) and an increase in the protein levels of 70 thermal shock associated with preterm birth.

Heat stress is a function of the interaction of internal heat production, the capacity of the loss of heat to the environment and environmental heat load. During pregnancy, it increases the deposition of fat and the in-house production of heat due to fetal growth and metabolism.

The experts concluded that these factors limit the ability of pregnant women to reduce heat stress and make them more prone to this.

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Bibliographic reference:

Tillett T. Pregnancy Pause: Extreme Heat Linked to Shortened Gestation ”. Environmental Health Perspectives 119:a443 – a443, October 2011.