Heat Stress and the Pregnant Mother.


Given the change in social norms and the current economic climate it is not unusual see women remain at work well into the latter stages of their pregnancy. It is important when considering the impact of heat stress on the working population that special consideration is given to the pregnant mother and her unborn child.

In a study undertaken in the 1970’s (Edwards et al, 1978), significant potential damage of heat in many mammalian species was identified. The flow on to this has been the recognition of a similar effect in humans.

There is strong evidence to suggest that exposures to elevated temperatures during pregnancy can result in serious consequences to the unborn child particularly in the first trimester. It is at this stage where there is significant cell development and multiplication occurring. This can also be at a time where the new mother is unaware that she is pregnant or in some cases would prefer to keep the pregnancy private for the first trimester.

In a recent literature review presented at the 2015 Australian Institute of Occupational hygienists conference (Di Corleto & Di Corleto, 2015), a number of significant potential impacts were identified. These are presented in a table below.

Hyperthermia related bio-effects. (Adapted from Edwards et al 2003)

Early developmental effects (Embryonic) Mid – late foetal effects
Anencephaly Pre-term delivery
Spina bifida Growth retardation
anophthalmia Abortion
Resorption or abortion Learning deficits
Heart anomalies Blindness
Neural tube defects Cleft lip
Central nervous system

There can also be issues in the later term. A University of Montreal study in 2014 assessed data from over 300,00 births in the Montreal region in Canada over the period 0f 1981 to 2010. It found that for pregnant women who reached 37 – 38 weeks of the term there was a 17% risk of early term delivery following a three-day episode of 32°C or more. This increased to 27% if the episode lasted form 4 – 7 days (Auger et al 2014).

It is difficult to pinpoint a core body temperature increase threshold at which these occur. The impact of the temperature elevation is very dependent on the stage of the pregnancy and hence those particular mechanisms occurring in the embryonic or foetal development (Di Corleto & Di Corleto, 2015). It is thus very important that when talking with pregnant women in the workforce the health professional whether medical practitioner, occupational physician, obstetrician or occupational hygienist must ask that most important question; “What is your occupation?” This will help identify potential exposures.


There is strong evidence in the literature that exposure to elevated temperatures during pregnancy can result in harm to the unborn child and the mother.


Auger, N.,Naimi A., Smargiassi A., Lo, E., Kosatsky,T.,(2014). Extreme Heat and Risk of Early Delivery Among Preterm and Term Pregnancies. Epidemiology • Volume 25, Number 3.  pp344-350

Di Corleto, E. M. and Di Corleto, R., (2015). Are you adequately protecting working mothers? A review of key reproductive workplace physical hazards associated with pregnancy. Proceedings of the Australian Institute of Occupational hygienists conference, Perth, Australia.  (attached) Are you adequately protecting working mothers FD

Edwards, M.J., (1978). Congenital defects due to hyperthermia. Anv. In Vet. Sci & Comparative Medicine. 22:29-52

Edwards, M.J., Saunders, R.D., Shiota, K., (2003). Effects of heat on embryos and foetuses. International Journal of Hyperthermia, 19:3, 295-324

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