Our changing climate may compromise the health of our babies before they’ve even exited the womb.
There’s growing evidence extreme temperatures and natural disasters are linked to premature births, stillbirths and even abnormal gestational weight and size in many parts of the world — including Australia.
And with global temperatures on the up and up, and natural disasters becoming more frequent, the World Health Organisation (WHO) says mothers and their babies are in danger.
“Climate change is a growing threat to maternal, newborn and child health that can no longer be ignored,” the WHO says.
Inaction could even mean we lose some of the hard-won advances for maternal and newborn survival we’ve made in recent decades.
But the capacity for expectant mothers, particularly the most marginalised, to shield themselves from environmental stressors is pretty limited.
There are around 15 million pre-term births around the world each year but a hotter Earth could mean we see even fewer full-term deliveries.
Researchers who studied almost 1 million mothers in New South Wales founda 16 per cent higher risk of having a pre-term birth (when a baby is born before 37 weeks) if you live in the top 5 per cent hottest parts of the state.
Globally, pre-term births are the leading cause of death for children under five. They can cause lifelong health issues including lung disease and physical or intellectual disabilities.
While it’s well established that natural disasters can affect the foetus, Professor Behie says we don’t know why this happens.
“We’re assuming it’s due to high stress felt by the mother but we don’t understand how that stress actually gets to the foetus.”
While the exact mechanism is unclear, there may be a number of factors.
Understanding the secrets of stress
When a woman is pregnant her whole body is under stress — her heart pumps harder and she is close to the maximum sustainable energy output a human can endure.
Add thermal stress to the mix and the body can malfunction.
Extreme temperatures can cause systematic inflammation and oxidative stress, which have troubling flow-on effects for the foetus.
It can mean there’s less blood flowing to the uterus and the baby receives less of the essential nutrients it needs to grow, Dr Nyadanu says.
Alternatively, it can also cause high blood glucose, which can be transported to the developing foetus and increase its size.
Stress also causes your body to produce more cortisol (the stress hormone), Professor Behie adds.
“And really big spikes in cortisol for a long time … can interfere with other hormones (like oestrogen) and induce pre-term labour.”
But she believes another factor called the life history theory might be the reason why stress affects foetal development.
It’s the evolutionary premise that living things must make trade-offs due to energy constraints and the body may decide to divert resources away from reproduction.
“In a really stressful environment, the body might be getting the signal that it’s not an optimal time to reproduce so it may invest in the mother’s survival over the baby’s and go on to reproduce at a time when resources are better,” Professor Behie says.
But there’s still more questions, as not every woman who lives through a natural disaster has a pre-term birth.
Need for better disaster planning
Professor Behie says it’s critical to understand how environmental stressors impact birth outcomes so we can safeguard the health of Australia’s children.
Having to evacuate and being separated from social networks often causes expectant mothers the most stress during a natural disaster, and women born outside of Australia are particularly vulnerable, she adds.
“The added layer for women who have moved here is they don’t have the same level of risk perception as they may not have been exposed to bushfires for example.”
Australian disaster guidelines advise women over 36 weeks gestation to factor extreme weather events such as cyclones into their birth plan due to risk of being cut off in an emergency and the higher incidents of premature labour, but there are no guidelines for women in earlier stages of pregnancy.
This differs to the US where health authorities have disaster guidelines for women at any stage of pregnancy.
“We need to take this seriously as a reproductive health issue and think about how pregnant women are quite a vulnerable group as our environment changes,” Professor Behie says.
Dr Nyadanu believes meteorological bodies should issue specific warnings for pregnant women and instruct them not to leave the house when it’s too hot or cold.
He believes there should also be “public protective centres” for women who don’t have air-conditioning at home.
“But more than that, we need to shift away from fossil fuels [if we’re going to] ensure birth outcomes aren’t affected by climate change.”
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