During pregnancy, the placenta is the lifeline between mother and baby. It supplies the foetus with oxygen and nutrients, removes waste products and acts as a partial shield against harmful substances. But it is not an impenetrable barrier.
Authors
- Priya Bhide
Clinical Reader Women’s Health Research Unit, Centre for Public Health and Policy, Queen Mary University of London
- Nelima Hossain
Academic Trainee, Public Health, Queen Mary University of London
A 2023 systematic review found evidence that microplastics - tiny plastic particles less than five millimetres in size - may be able to cross from the mother's bloodstream into the foetus. If confirmed, this could have serious consequences for development during pregnancy and for the long-term health of future generations.
Plastic waste does not simply disappear. Over time, sunlight, environmental conditions and mechanical wear break it down into smaller and smaller fragments: from large pieces known as macroplastics, to mesoplastics, to microplastics and eventually to nanoplastics : particles less than 100 nanometres across, small enough to be measured on the scale of molecules.
These particles come from the breakdown of everyday items: polyethylene from plastic bags and bottles, polypropylene from food containers and straws, polystyrene from takeaway cups and packaging, polyethylene terephthalate (PET) from drinks bottles, and polyvinyl chloride (PVC) from pipes, toys and clothing.
A 2025 review examining research in animals, lab-grown cells and human tissue samples found that both microplastics and nanoplastics can cross the placental barrier. Once inside, they may disrupt the delicate workings of the fetoplacental unit - the combined system of placenta and foetus - in several ways.
Studies suggest microplastics can block or interfere with the normal pathways cells use to communicate, trigger programmed cell death (apoptosis), and cause oxidative stress - a form of cellular damage that occurs when harmful oxygen-containing molecules build up faster than the body can neutralise them. Some plastics may also disrupt the endocrine system, which controls hormone release essential for growth and development.
The ability to cross the placental barrier is especially concerning because this barrier normally acts as a highly selective filter, protecting the developing foetus from many harmful substances while allowing essential nutrients and oxygen through. If plastics bypass these defences , they could interfere with organ formation and long-term health during one of the most vulnerable stages of human development.
Exactly how these particles cross into the placenta is still not fully understood . Factors such as particle size, weight and surface charge - the tiny electrical charge carried by a particle - seem to play a role, as does the biological environment they move through.
Experiments using human placental models found that larger polystyrene particles (50-500 nanometres) did not damage placental cells and, in some cases, even seemed to improve their survival. By contrast, much smaller particles (20-40 nanometres) caused some cells to die and slowed the growth of others.
Animal studies show mixed results. In some experiments, most nanoplastics stayed in the placenta, with only a small amount reaching the foetus. In studies using human placentas in the lab, larger particles were usually trapped, while smaller ones could pass through in limited amounts.
Other research has found that nanoplastics can travel into foetal organs, including the brain, lungs, liver, kidneys and heart. Even when these organs looked normal under the microscope, researchers sometimes found smaller placentas and lower birth weights - changes that can affect a baby's health.
Overall, this suggests that not all nanoplastics are dangerous, but certain sizes and types may pose real risks during pregnancy.
Critical window for microplastic harm
Foetal development is a finely tuned process, with cell growth, movement and death all tightly regulated. This makes it particularly vulnerable to environmental "insults" during critical windows of development . According to Barker's foetal reprogramming theory , also known as the "developmental origins of health and disease" hypothesis, the conditions in the womb can "programme" how a baby's organs, tissues and metabolism develop.
Harmful exposures during pregnancy, such as poor nutrition, toxins, stress, or pollutants like microplastics , can permanently alter the way organs form and function. These changes might not cause illness immediately, but they can increase the risk of chronic conditions such as diabetes, high blood pressure and heart disease later in life.
For example, if the placenta is damaged or nutrient supply is restricted, the foetus may adapt by prioritising blood flow to the brain at the expense of other organs. While this can help survival in the short term, it may result in smaller kidneys, altered metabolism or changes in blood vessel structure, all of which carry long-term health consequences.
Microplastics consumed through food or water may also disrupt the gut's delicate balance of microbes , damage the intestinal lining, interfere with nutrient absorption and change how fats and proteins are processed.
Laboratory experiments show that polystyrene nanoparticles can enter embryos, accumulate in multiple organs and cause effects such as a slowed heart rate and reduced activity, even at very low doses. When inhaled by the mother, these particles can travel to the placenta and on to the foetal brain and heart.
There is also concern about potential effects on the developing brain. Some studies indicate that microplastics can build up in regions vital for learning, memory and behaviour, including the cerebellum, hippocampus and prefrontal cortex. Once there, they can cause oxidative damage, change the levels of neurotransmitters (the brain's chemical messengers) and switch off certain genes needed for healthy brain development.
In animals, prenatal exposure to microplastics has been linked to anxiety-like behaviour, impaired learning, abnormal patterns of nerve cell growth, thinner brain tissue and disrupted connections between neurons.
Gaps in knowledge
Despite these worrying signs, there is still much we do not know. Research in this area is hampered by the fact that most studies are done in animals or in controlled laboratory settings, with little direct evidence from pregnant women .
We still do not fully understand how microplastics travel through the body, how much can accumulate in the placenta and foetus, or how easily they can be cleared .
What is clear is that further research is urgently needed. Understanding whether microplastics pose a genuine threat to reproductive health and foetal development could help shape policies on plastic production, consumption and disposal - and inform the advice given to women during pregnancy.
The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.
