Effects of Microplastics on Pregnancy

What are the effects of microplastic exposure during pregnancy?

Research shows that maternal exposure to microplastics during pregnancy disrupts maternal physiology, compromises placental integrity, and impairs fetal growth and development.

Abstract

Microplastic exposure during pregnancy shows measurable impacts on maternal physiology, placental integrity, and fetal development. In rodent studies, exposure to primarily polystyrene and polyethylene particles via drinking water, oral gavage, or inhalation has been associated with the following outcomes:

1. Maternal changes such as altered cardiovascular parameters (e.g., increased heart and spleen weight, vascular dysfunction), reproductive delays (e.g., disturbed estrous cyclicity and diminished fertility), metabolic disruptions, and shifts in liver weight or function.
2. Placental findings that include accumulation of microplastics (with one report noting a mean concentration of 6.91 mg/g in 100% of placentae) and altered vascular flow—up to a 43% increase in umbilical artery flow in one study.
3. Fetal effects marked by growth restriction—for example, a 12% reduction in fetal weight at 106 ng/L exposure—and neurodevelopmental disruptions, including hippocampal ferroptosis, reduced myelin formation, and altered neurotransmitter levels.

Biochemical assessments reveal increased oxidative stress, inflammation, and modulated gene expression linked to lipid metabolism and angiogenesis. In several experiments, higher doses (for instance, exposures equivalent to levels producing dose-dependent effects in mice) correspond with more pronounced adverse outcomes. These findings indicate that microplastic exposure during gestation may perturb maternal, placental, and fetal systems in measurable ways.

Methods

We analyzed 40 sources from an initial pool of 499, using 5 screening criteria. Each paper was reviewed for 5 key aspects that mattered most to the research question.

Paper search

Using your research question “What are the effects of microplastic exposure during pregnancy?”, we searched across over 126 million academic papers from the Semantic Scholar corpus. We retrieved the 499 papers most relevant to the query.

Screening

We screened in sources based on their abstracts that met these criteria:

• Study Population: Does the study include pregnant humans or animals AND report clear pregnancy-related outcomes?
• Exposure Assessment: Does the study examine microplastic (not macroplastic) exposure through any route (ingestion, inhalation, or dermal) using clear assessment methodology?
• Outcome Measures: Does the study measure specific maternal, fetal, or pregnancy outcomes during any stage of pregnancy?
• Study Design: Is the study either a primary research study (experimental or observational) or systematic review with a sample size of at least 10?
• Exposure Quantification: Does the study include biological measurements or outcomes related to microplastic exposure (not just environmental concentrations)?

We considered all screening questions together and made a holistic judgement about whether to screen in each paper.

Data extraction

We asked a large language model to extract each data column below from each paper.

• Study Design:

Describe the specific type of experimental design used in the study. Look in the Methods section for details such as:

• Type of study (e.g., animal experimental study, in vivo experiment)

  • Specific model used (e.g., pregnant mice, pregnant rats)
  • Experimental groups (number and type)

• Participant Characteristics:

Extract specific details about the study subjects:

• Species used (e.g., ICR mice, rats)

  • Strain or type of animal
  • Pregnancy stage or gestational age at start of experiment
  • Number of animals per group
  • Age of animals (if reported)
  • Sex (though likely all female for pregnancy studies)

• Microplastic Characteristics:

Capture detailed information about the microplastics used:

• Type of microplastic (e.g., polyethylene, polystyrene)

  • Particle size (in μm or mm)
  • Concentration of exposure (include units)
  • Method of administration (e.g., intragastric intubation, pulmonary exposure)
  • Duration of exposure

• Primary Outcomes Measured:

List all primary outcomes examined in the study related to pregnancy and microplastic exposure:

• Maternal outcomes (e.g., body weight, glucose homeostasis, organ function)

  • Fetal/offspring outcomes (e.g., birth weight, organ weight, developmental markers)
  • Biochemical markers (e.g., acetylcholinesterase, glutathione peroxidase)

• Key Findings:

Summarize the most significant findings of the study:

• Statistically significant changes in maternal or fetal outcomes
  • Observed biological mechanisms
  • Dose-dependent effects
  • Potential implications for pregnancy health

Results

Characteristics of Included Studies

Based on the information extracted from the included studies, we observed the following patterns:

• Study Design:
  • Animal experimental: 33 studies
  • Observational: 6 studies
  • In vitro: 2 studies
  • Systematic review: 1 study
• Microplastic Type:
  • Polystyrene: 28 studies
  • Polyethylene: 8 studies
  • Various or not specified: 4 studies
• Microplastic Size:
  • Nanoplastics: 19 studies
  • Microplastics: 15 studies
  • No size information found: 8 studies
• Exposure Route:
  • Drinking water: 5 studies
  • Detection in placenta: 5 studies
  • Oral gavage: 4 studies
  • Intratracheal instillation: 3 studies
  • Maternal transfer: 2 studies
  • No exposure route information found: 7 studies
• Species/Model:
  • Mice: 25 studies
  • Rats: 8 studies
  • Human: 7 studies
  • Other (e.g., chick embryos, cell lines): 2 studies

The extracted data indicates that many of the included studies were animal experiments, often using mice models, and frequently examining polystyrene nano- and microplastics. The diversity in exposure routes reflects the complex nature of microplastic exposure in biological systems.

Effects of Microplastic Exposure

Maternal Effects

The studies reported various maternal effects associated with microplastic exposure during pregnancy:

• Effect Categories:

  • Body weight: 3 studies
  • Reproductive: 2 studies
  • Metabolic: 2 studies
  • Hepatic: 2 studies
  • Other categories (Cardiovascular, Mammary gland development, Organ deposition, Organ weight, Uterine changes, Immune system, and Liver weight): 1 study each
  • No effect categories found: 21 studies
  • Not applicable (observational studies): 6 studies

• Observed Changes: 13 out of 40 studies reported specific observed changes. These changes varied widely, including effects on body weight, reproductive system, metabolism, liver function, cardiovascular system, and immune system.

• Exposure Levels: 22 out of 40 studies reported exposure levels. The exposure levels varied greatly in both units and magnitudes, ranging from ng/L to mg/kg/day.

• Statistical Significance: Only 1 out of 40 studies reported statistical significance of the results.

The wide range of effect categories and exposure levels studied reflects the complexity of microplastic exposure during pregnancy. However, the lack of consistency in reporting observed changes and statistical significance across the studies makes it challenging to draw definitive conclusions about the overall effects of microplastic exposure on maternal health.

Placental and Fetal Effects

The included studies reported a variety of effects associated with microplastic exposure during pregnancy and early postnatal development, potentially affecting multiple organ systems and developmental processes:

• Most Frequently Studied Systems:
  • Fetal growth: 16 studies
  • Placenta: 10 studies
  • Neurodevelopment: 7 studies
  • Hepatic system: 5 studies
• Most Commonly Observed Changes:
  • Fetal weight decrease or reduced birth weight: 11 studies
  • Neurodevelopmental effects: 7 studies
  • Fetal growth restriction or effects: 6 studies
  • Microplastic presence or accumulation: 4 studies
  • Placental dysfunction or damage: 4 studies
• Key Findings Across Studies:
  • Fetal growth effects or restriction: 13 studies
  • Neurodevelopmental effects: 7 studies
  • Placental effects: 6 studies
  • Microplastics detected in placenta or meconium: 4 studies
  • Hepatic effects: 3 studies

Multiple studies reported significant effects on fetal growth, neurodevelopment, and placental function. Several studies also detected microplastics in placental tissue and meconium. Additionally, we found reports of metabolic changes, reproductive effects, and multi-system impacts in offspring exposed to microplastics during development.

Biochemical and Molecular Changes

The studies reported a range of biochemical and molecular changes associated with microplastic exposure during pregnancy:

• Oxidative Stress:
  • Huang et al. (2022) observed increased malondialdehyde generation and altered superoxide dismutase and catalase activities in offspring tissues.
  • Yu et al. (2024) noted increased oxidative stress in lung tissues of offspring.
• Inflammation:
  • Kim and Kim (2022) reported increased levels of inflammatory markers such as monocyte chemoattractant protein-1 and tumor necrosis factor-alpha in neonatal livers.
  • Zhang et al. (2022) observed increased levels of IL-1β, IL-6, and TNF-α in fetal brain regions.
• Metabolic Alterations:
  • Chen et al. (2022) found disturbances in cholesterol metabolism and complement and coagulation cascades pathways in the placenta.
  • Luo et al. (2019b) reported alterations in serum metabolites, including amino acids and acyl-carnitines, indicating potential fatty acid metabolism disorders.
• Gene Expression Changes:
  • Wang et al. (2023) reported upregulation of genes involved in de novo lipogenesis, fatty acids uptake, and triacylglycerol synthesis in maternal and offspring livers.
  • Xiong et al. (2024) identified dysregulation of genes involved in angiogenesis and visual system development in the retina.
• Hormonal Changes:
  • Dou et al. (2024) observed elevated testosterone levels in female mice exposed to microplastics.
• Neurotransmitter Alterations:
  • Yang et al. (2022) reported reduced γ-aminobutyric acid (GABA) levels in the prefrontal cortex and amygdala of offspring.
  • Tian et al. (2024) observed alterations in monoamine and amino acid neurotransmitters in the cortex and hippocampus.
• Cellular Apoptosis:
  • Wan et al. (2024) observed increased apoptosis in placental tissues, associated with activation of the Bcl-2/Cleaved-caspase-2/Cleaved-caspase-3 signaling pathway.
• Epigenetic Changes:
  • Dou et al. (2024) reported changes in pathways related to DNA methylation and histone modification in offspring.

These biochemical and molecular changes varied depending on the type and size of microplastics, exposure route, and the particular organ system affected.

Dose-Dependent Relationships

Several studies reported dose-dependent effects of microplastic exposure during pregnancy:

• Fetal Growth:
  • Chen et al. (2024a) observed dose-responsive harmful effects on fetal development, with moderate intake (equivalent to 3.3 cups/day) significantly altering cecal microbiome composition and metabolic functions.
  • Aghaei et al. (2022) reported a 12% decrease in fetal weight at the highest exposure concentration (106 ng/L).
• Placental Effects:
  • Zhang et al. (2022) found that maternal exposure to polystyrene nanoplastics caused dose-dependent structural damage to the placenta.
• Hepatic Effects:
  • Huang et al. (2022) and Oteyola et al. (2022) both reported dose-dependent effects on liver weight, oxidative stress, and inflammation in offspring, with more pronounced effects at higher doses.
• Neurodevelopmental Effects:
  • Zhang et al. (2022) observed that smaller particle sizes and higher doses had more significant neurotoxic effects on fetal development.
• Reproductive Toxicity:
  • Wan et al. (2024) found that exposure to polystyrene nanoplastics at doses of 50 or 100 mg/kg induced miscarriage in a dose-dependent manner.
• Metabolic Effects:
  • Wang et al. (2023) reported dose-dependent effects on hepatic steatosis development in dams and adult female offspring.
• Microplastic Accumulation:
  • Song and Kim (2021) observed a dose-dependent accumulation of microplastics in neonate organs.

Not all studies found clear dose-dependent relationships. For example, Tang et al. (2023) reported that while exposure to polystyrene nanoparticles caused significant effects, these did not follow a classic dose-dependent pattern.

The presence of dose-dependent effects in many studies suggests that there may be threshold levels of exposure below which effects are minimal or undetectable. However, the exact thresholds likely vary depending on the specific outcome measured, the type and size of microplastics, and the route of exposure.

Route-Specific Effects

Oral Exposure Outcomes

Oral exposure to microplastics during pregnancy, typically through drinking water or gavage, was a common route of administration in many of the included studies. The outcomes associated with oral exposure were diverse and affected multiple systems:

• Fetal Growth:
  • Chen et al. (2022) found significant declines in fetal weights at higher concentrations (10 mg/L) of polystyrene nanoplastics in drinking water.
  • Chen et al. (2024a) observed dose-dependent fetal growth restriction with oral gavage of polystyrene microplastics.
• Placental Effects:
  • Dibbon et al. (2023) reported altered umbilical artery blood flow and placental dysfunction in mice exposed to polystyrene micro- and nanoplastics through drinking water.
• Metabolic Effects:
  • Luo et al. (2019a) found that oral exposure to polystyrene microplastics led to metabolic disorders in dams, associated with gut microbiota dysbiosis and gut barrier dysfunction.
  • Wang et al. (2023) observed hepatic steatosis in dams and adult female offspring following oral exposure.
• Neurodevelopmental Effects:
  • Chen et al. (2024b) reported that oral exposure to polystyrene nanoplastics during gestation and lactation caused ferroptosis in the hippocampus of offspring, leading to cognitive deficits.
• Reproductive Effects:
  • Dou et al. (2024) found that oral exposure to polystyrene microplastics during lactation led to reproductive toxicity in female mice and their male offspring.
• Cardiovascular Effects:
  • Hanrahan et al. (2024) observed significant changes in placental function, including increased umbilical artery blood flow, in mice exposed to polyethylene micro- and nanoplastics through drinking water.
• Oxidative Stress and Inflammation:
  • Kim and Kim (2022) reported oxidative stress and inflammation in neonatal livers following maternal intragastric administration of polyethylene microplastics.
• Transgenerational Effects:
  • Zhang et al. (2023) found that oral administration of microplastics led to reduced birth weight and impaired reproductive outcomes in female offspring.

The effects appear to be influenced by factors such as the type and size of microplastics, the dose, and the duration of exposure.

Respiratory Exposure Outcomes

Several studies examined the effects of respiratory exposure to microplastics during pregnancy, typically through intratracheal instillation or inhalation:

• Fetal Growth and Development:
  • Cary et al. (2024) found that a single pulmonary exposure to polystyrene nanoplastic in late-stage pregnancy led to reduced fetal and placental weight.
• Cardiovascular Effects:
  • Cary et al. (2024) also reported increased heart weight and vascular dysfunction in the aorta of exposed dams, as well as dysregulation of fetal heart, aorta, and umbilical artery function.
• Placental Translocation:
  • Fournier et al. (2020) demonstrated that nanopolystyrene particles administered via intratracheal instillation could cross the placental barrier and be detected in fetal tissues.
• Organ Deposition:
  • Han et al. (2021) observed dose-dependent accumulation of polyethylene microplastics in various organs of neonates following maternal intratracheal instillation.
• Oxidative Stress and Inflammation:
  • Kim and Kim (2022) reported increased oxidative stress and inflammation markers in neonatal livers following maternal intratracheal instillation of polyethylene microplastics.
• Hepatic Effects:
  • Wang et al. (2023) found that gestational exposure to polystyrene nanoplastics via inhalation induced hepatic steatosis in the dam and adult female offspring.

These findings highlight that respiratory exposure to microplastics during pregnancy can have significant and wide-ranging effects on both maternal and fetal health. The ability of inhaled microplastics to cross the placental barrier and affect fetal development is particularly notable. The differences in outcomes between oral and respiratory exposure routes suggest that the mode of exposure can influence the distribution and effects of microplastics in the body. This highlights the importance of considering multiple exposure routes when assessing the overall risk of microplastic exposure during pregnancy.

References

• R. K. Sharma, Usha Kumari, Sudhir Kumar (2024). Impact of Microplastics on Pregnancy and Fetal Development: A Systematic Review. Cureus
• Qiong Chen et al. (2024). Microplastics from disposable paper cups are enriched in the placenta and fetus, leading to metabolic and reproductive toxicity during pregnancy. bioRxiv
• Youngmi Song, Changyul Kim (2021). Toxicities Demonstrated in Dams and Neonates following Intragastric Intubation of Polyethylene Microplastics to Pregnant Mice. Journal of Environmental Health Sciences