As the impacts of climate change intensify, we are already seeing its effects on the health of our patients and their communities. Throughout most of Australia and Aotearoa New Zealand our summers are becoming hotter and our bushfire seasons longer and more intense. These extreme weather events are also major public health threats and cause significant morbidity and mortality.¹ The recently released National Climate Risk Assessment estimates that in parts of Australia, heat related mortality will increase by 450% at the current trajectory of 3°C of global warming.² It is important to note that a heatwave is relative to the average temperatures specific to a place at that time of the year, so health effects can occur at lower temperatures earlier in the season or in places where the average temperatures are lower.  Both heat stress and bushfire exposure can adversely impact pregnancy and reproductive outcomes and negatively impact mental health. Furthermore, the health impacts on pregnant people can affect the health and wellbeing of future generations.^3,9

Extreme Heat: What Are the Risks?

Pregnancy-related physiological changes confer increased susceptibility of pregnant people to extreme heat. Multiple mechanisms have been proposed and likely act in concert to mediate adverse pregnancy outcomes. Possible mechanisms include increased metabolic rate, decreased surface area to mass ratio, dehydration-related release of prostaglandins and oxytocin and altered placental perfusion. Women in lower-socioeconomic groups, rural populations, Indigenous communities, ethnic minorities, as well as mothers at extremes of age or with chronic conditions like diabetes or depression, are more likely to be impacted.⁴ 

Preterm Birth

A recent systematic review and meta-analysis published in the British Medical Journal found that the likelihood of preterm birth increased by 5% per 1°C increase in temperature, and by 16% during heatwaves.⁴ Most studies reported dose-response associations, where rates of preterm birth rose progressively with increasing temperatures and longer durations of heat exposure. Exposure timing and lag windows varied between studies, with increased preterm birth risk associated with exposure during the month of conception right through to the final week of pregnancy.⁴

Stillbirth

Heat and stillbirth also display a dose-response relationship with stillbirth risk increasing by 5% per 1°C increase in temperature. Of note, these studies were conducted in high income countries.4 A Brisbane study found heat wave exposure in all months of pregnancy was associated with increased stillbirth while a Western Australian study found the final weeks of gestation to be the highest risk exposure period.^5,6 

Subfertility

There has been limited human-specific research into the effects of heat on fertility.^7,8 In a single centre cohort study of 631 women who attended a fertility centre at an academic US hospital, a small but statistically significant reduction in antral follicle count of 1.6% was associated with every 1°C increase in average maximum temperature during the 90 days prior to ovarian reserve testing.⁸

Mental Health 

There is clear evidence of increased mental health related emergency department presentations and hospital admissions in hotter weather, in addition to an increased incidence of physical and sexual assault and domestic violence.⁹ Pregnancy combined with severe mental illness increases the risk for psychiatric emergencies during hot weather.⁹

Bushfires: What Are the Risks?

Climate change is increasing bushfire frequency and severity across large parts of Australia due to increases in extreme heat, drought and storms.^2,3 Recent megafires linked to climate change include the ‘Black Summer Fires’ (2019-2020) and Victoria’s ‘Black Saturday Fires’ (2009). These fires caused significant loss of life, in addition to devastating health, social, economic and environmental impacts.^2,13 Air pollutants such as fine particulate matter (PM2.5) from bushfire smoke have been associated with adverse pregnancy and fertility outcomes, affecting nearby and down-wind populations. 

Preterm Birth

An Australian cohort study found small but significant increases in preterm birth and decreases in birth weight following the 2009 Black Saturday bushfires compared to women living in unaffected areas.10 A larger epidemiological study from California, USA, examined more than 3 million births, finding that 3.7% excess preterm births can be attributed to wildfire smoke in 2007-2012, and up to 6% excess preterm births in high smoke years.¹¹  

Subfertility 

Particulate matter (PM2.5) has also been shown to be associated with impaired sperm and oocyte quality, reducing fertility by 2% for every increase in 10 units of concentration in the air.¹² The impact can be significant when levels of PM2.5 in Melbourne were recorded above 300 µg/m3 during the Black Summer bushfires, well above the Australian National Air Quality Standard (‘very poor’ air quality >50 µg/m3).¹³

Mental Health

Communities affected by the Victorian Black Saturday bushfires had increased rates of post-traumatic stress disorder, depression, and alcohol misuse 3-4 years after the event.¹⁴ Despite limited research, there is evidence to suggest that gender-based violence increased significantly in communities affected by the Black Saturday fires, which is consistent with studies conducted in the aftermath of climate-related disaster events in New Zealand and internationally.¹⁵

What Can We Do? 

1. Inform patients to avoid heat stress on hot days e.g., stay hydrated, stay indoors, exercise inside or during cool parts of the day, access cooled public spaces like libraries and community centres.  
2. Educate patients on the symptoms of heat stress and ensure they know when to seek medical attention.  
3. Advise patients to check air quality alerts (IQAir) and access the RANZCOG Air Pollution & Pregnancy Patient Information Pamphlet which contains recommendations to reduce exposure.  
4. Educate patients and other care providers e.g., GPs, midwives on how extreme weather can exacerbate comorbidities. 
5. Embed sustainable healthcare practices within our clinical practice, hospital and healthcare services to reduce greenhouse gas emissions e.g., switching to renewable electricity, avoiding investigations that do not alter clinical management, choosing reuseable medical equipment over single use where possible.  

As obstetricians & gynaecologists, we have the unique opportunity to interact with families at some of life’s most pivotal moments. It is our responsibility to educate and protect women’s health by minimising the impacts of climate change and advocating for evidence-based climate action from government and institutions.