RESEARCH STARTER

Environmental birth defects

Environmental birth defects refer to developmental issues in fetuses linked to pollutants that parents may encounter before conception or that mothers are exposed to during pregnancy. These defects can manifest in various forms, including growth retardation, physical malformations, or even fetal death, with severity influenced by factors such as the timing of exposure and the level of the toxic substance. Research indicates that around 3% of birth defects in the U.S. are caused by environmental factors, with an additional 25% potentially involving gene-environment interactions. Substances known to cause these defects include heavy metals like mercury and lead, as well as various chemical agents such as dioxins and pesticides. Historical incidents, such as the Minamata disease outbreak in Japan and the Bhopal gas tragedy in India, highlight the profound impact of industrial pollution on fetal health. Moreover, military exposure to toxic chemicals, such as Agent Orange during the Vietnam War, has been linked to increased birth defects in veterans' offspring. The Zika Virus also emerged as a contemporary concern, associated with significant birth defects like microcephaly when pregnant women become infected. Understanding these risks underscores the importance of environmental health in safeguarding fetal development.

Full Article

DEFINITION: Problems in fetal development related to environmental pollutants to which parents are exposed before conception or to which pregnant women are exposed during pregnancy

Embryotoxic agents encountered through environmental exposure can cause a variety of congenital anomalies, ranging from developmental delays to malformations and death. The severity of any particular anomaly results from a combination of factors, including the gestational age at which the fetus is exposed to the agent and the effective dose of the toxic substance.

According to the March of Dimes Foundation, congenital anomalies, sometimes called birth defects or congenital abnormalities, affected about one in every thirty-three babies (3 percent) born in the United States in the mid-2020s, and these babies account for more than 20 percent of the country’s infant deaths. Some congenital anomalies are caused by environmental exposure to teratogens (substances that cause developmental malformations). The cause of up to 70 percent of congenital anomalies is unknown; however, studies estimate that environmental factors directly contribute to between 3 and 10 percent of cases and play a role in up to 25 percent through gene-environment interactions. Some health conditions or lifestyle factors increase one's risk of having a child with one of these conditions, including diabetes, substance use disorder, obesity, some genetic predispositions, being over thirty-five, certain antidepressants, and tobacco use.

In the US, the National Birth Defect Registry, assembled through responses to a questionnaire designed by Birth Defect Research for Children (formerly the Association of Birth Defect Children), details maternal and paternal exposure to environmental agents, including chemicals, radiation, pesticides, lead, and mercury. In March 1998, the US Congress passed the Birth Defects Prevention Act, which continued the National Birth Defects Prevention Study, a research project begun in 1996 to gather data on congenital anomalies, including possible environmental causes.

Teratogenic Agents

Chemical agents known to cause environmental congenital anomalies in animals and humans include compounds of heavy metals (especially mercury, lead, and thallium), urethane, dioxin-like chemicals, various steroids, sex hormones (including xenoestrogens and antiandrogenic pesticides), and trypan blue, an agent once used to treat mange. Chemical agents disturb intracellular chemistry; embryonic changes usually precede placental changes. Other teratogenic agents include polychlorinated biphenyls (PCBs), solvents (benzene), plastics like Bisphenol A (BPA), air pollution, secondhand smoke from any type of tobacco product, and radiation, or chemotherapy medicines

Testing of some agents has shown increases in the frequency of common malformations. For example, dioxin and similar chemicals have been observed to increase cleft palate and hydronephrosis (a swelling of the kidneys caused by obstructed urine flow) in mice. A minimum of two species of animals, studied at a minimum of three dose levels, is essential for teratogenic testing. Strong teratogenic agents usually produce similar malformations in different species. Agents that produce demonstrable congenital anomalies in animals, especially in higher primates such as baboons, are presumed capable of producing congenital anomalies in a human fetus.

Prenatal exposure to ionizing radiation is another environmental factor known to cause congenital anomalies. For this reason, patients must disclose pregnancies to radiologic technicians before X-ray sessions so that the technician can minimize risks. Modern X-ray technology involves a very low exposure risk for the fetus; most problems result from accidental exposure or from necessary therapy. Exposure to large, fluctuating electromagnetic fields (EMFs) was previously suspected as a cause of environmental congenital anomalies. Speculation that high-voltage electric power transmission lines might cause environmental congenital anomalies or childhood cancer led to many epidemiological studies using small mammals; however, animal studies conducted over many years did not establish any link between high-voltage lines and congenital anomalies. Studies into the genotoxic potential (ability to alter genetic material) of EMFs have been conducted with bacteria, fruit flies, and mice. Although some cell research has suggested that EMF exposure may negatively affect the ability of cells to repair normal damage to genetic material, most evidence has suggested that EMF exposure is not genotoxic.

Research also indicates that exposure to bisphenol A (BPA), a chemical found in some plastics, contributes to developmental problems. Scientists have also linked PCBs and industrial solvents like benzene to heart and neural tube defects.

March of Dimes recommends avoiding eating fish that are known to contain high levels of mercury during pregnancy, including king mackerel, swordfish, tilefish, and shark.

Examples

Clusters of environmental congenital anomalies within human populations sometimes arise as a result of exposure of multiple persons to a release of a teratogenic agent, especially when the food chain is contaminated. When consumed during pregnancy, organic mercury is a potent teratogen. The best-known widespread occurrence of organic mercury poisoning took place in the 1950s and early 1960s in Japan’s Minamata Bay, where industrial effluents containing high levels of mercury were pumped into the ocean for many years. This mercury was assimilated into seafood consumed by the local population, resulting in many cases of congenital Minamata disease.

In contrast to the environmental health problems at Minamata Bay, which took years to emerge, damage to human health was immediately apparent in Bhopal, India, after the catastrophic December 1984 industrial accident that released a lethal cloud of methyl isocyanate gas over a crowded shantytown. Some pregnancies were spontaneously aborted upon exposure to the gas. A 1987 study found that, of a sample of 865 surviving pregnant individuals who lived within a kilometer (0.6 mile) of the accident site when the incident occurred, only 57 percent gave birth to live children. Of those babies, 14 percent died within a month of delivery, an infant mortality rate about five times greater than what was common in the community before the accident. Many were born with severe developmental conditions or congenital anomalies. In the decades after the release, congenital anomalies were common in children born to individuals exposed to the gas, including cleft palate, joined or extra fingers, developmental delays, and mental problems. Soil and groundwater contamination from chemicals abandoned at the industrial site continues to poison area residents, giving rise to still more congenital anomalies.

Use of chemical agents during wartime is also associated with widespread congenital anomalies. Birth Defect Research for Children has collected data since 1990 concerning an elevated incidence of congenital anomalies and developmental disabilities in the children of US veterans of the Vietnam War. Heavy use of the dioxin-tainted defoliant Agent Orange in Vietnam is associated with a suite of deformities and ailments among the children of veterans. These include spina bifida; oral clefts; learning, attention, and behavioral disorders; and increased susceptibility to chronic childhood infections and to cancers later in life. Vietnamese researchers have found that, in comparison with background levels in their country, rates of congenital anomalies are four times higher in areas that were sprayed with Agent Orange during the war.

In 2016, officials at the World Health Organization (WHO) issued a public health emergency in response to the Zika virus, a mosquito-borne illness that could cause congenital anomalies if contracted during a pregnancy. The main concern caused by the virus was microcephaly, a condition in which a child is born with a smaller head and an underdeveloped brain. Although WHO lifted the emergency declaration by the end of 2016, the Zika virus continued to be an issue in some locations into the 2020s.


Bibliography

"About Us." Birth Defect Research for Children, birthdefects.org/about-us. Accessed 16 Sept. 2025.

"Birth Defects and Your Baby." March of Dimes, Dec. 2024, www.marchofdimes.org/find-support/topics/planning-baby/birth-defects-and-your-baby. Accessed 16 Sept. 2025.

Duan, Junchao, et al. “Global and Regional Burden of Congenital Birth Defects, 1990-2021: Persistent Healthcare Disparities and Emerging Challenges from Non-Fatal Health Burden.” BMJ Public Health, vol. 3, no. 1, 2025, doi:10.1136/bmjph-2024-001608. Accessed 16 Sept. 2025.

Hansen, Deborah Kay, and Barbara D. Abbott, editors. Developmental Toxicology. 3rd ed., Informa Healthcare, 2009.

Kofoed, Ane Bungum, et al. “Maternal Exposure to Airborne Polychlorinated Biphenyls (PCBs) and Risk of Adverse Birth Outcomes.” European Journal of Epidemiology, vol. 36, no. 8, 2021, pp. 861–72, doi:10.1007/s10654-021-00793-x. Accessed 16 Sept. 2025.

Lee, Kyung Shin, et al. “Environmental and Genetic Risk Factors of Congenital Anomalies: An Umbrella Review of Systematic Reviews and Meta-Analyses.” Journal of Korean Medical Science, vol. 36, no. 28, 2021, p. e183, doi:10.3346/jkms.2021.36.e183. Accessed 16 Sept. 2025.

Lipinski, Robert J., and Robert S. Krauss. Gene-Environment Interactions in Birth Defects and Developmental Disorders. Academic Press, 2023.

Liu, Hanjun, et al. “Emerging Trends and Cross-Country Health Inequalities in Congenital Birth Defects: Insights from the GBD 2021 Study.” International Journal for Equity in Health, vol. 24, no. 1, 2025, doi:10.1186/s12939-025-02412-7. Accessed 16 Sept. 2025.

Moore, Keith L., and T. V. N. Persaud. Before We Are Born: Essentials of Embryology and Birth Defects. 11th ed., Saunders/Elsevier, 2024.

Reshi, Mohd Salim, et al. Environmental Toxicology: Concepts and Principles. Jenny Stanford Publishing, 2025.

Sauvé, Sébastien. “Toxicology, Environmental Chemistry, Ecotoxicology, and One Health: Definitions and Paths for Future Research.” Frontiers in Environmental Science, vol. 12, 2024, doi:10.3389/fenvs.2024.1303705. Accessed 16 Sept. 2025.

Schardein, James L. Chemically Induced Birth Defects. 3rd ed., Marcel Dekker, 2000.

Shilpa S. Shetty, et al. “Environmental Pollutants and Their Effects on Human Health.” Heliyon, vol. 9, no. 9, 2023, p. e19496. doi:10.1016/j.heliyon.2023.e19496. Accessed 16 Sept. 2025.

"Zika Virus." World Health Organization, 8 Dec. 2022, www.who.int/news-room/fact-sheets/detail/zika-virus. Accessed 16 Sept. 2025.

Full Article

DEFINITION: Problems in fetal development related to environmental pollutants to which parents are exposed before conception or to which pregnant women are exposed during pregnancy

Embryotoxic agents encountered through environmental exposure can cause a variety of congenital anomalies, ranging from developmental delays to malformations and death. The severity of any particular anomaly results from a combination of factors, including the gestational age at which the fetus is exposed to the agent and the effective dose of the toxic substance.

According to the March of Dimes Foundation, congenital anomalies, sometimes called birth defects or congenital abnormalities, affected about one in every thirty-three babies (3 percent) born in the United States in the mid-2020s, and these babies account for more than 20 percent of the country’s infant deaths. Some congenital anomalies are caused by environmental exposure to teratogens (substances that cause developmental malformations). The cause of up to 70 percent of congenital anomalies is unknown; however, studies estimate that environmental factors directly contribute to between 3 and 10 percent of cases and play a role in up to 25 percent through gene-environment interactions. Some health conditions or lifestyle factors increase one's risk of having a child with one of these conditions, including diabetes, substance use disorder, obesity, some genetic predispositions, being over thirty-five, certain antidepressants, and tobacco use.

In the US, the National Birth Defect Registry, assembled through responses to a questionnaire designed by Birth Defect Research for Children (formerly the Association of Birth Defect Children), details maternal and paternal exposure to environmental agents, including chemicals, radiation, pesticides, lead, and mercury. In March 1998, the US Congress passed the Birth Defects Prevention Act, which continued the National Birth Defects Prevention Study, a research project begun in 1996 to gather data on congenital anomalies, including possible environmental causes.

Teratogenic Agents

Chemical agents known to cause environmental congenital anomalies in animals and humans include compounds of heavy metals (especially mercury, lead, and thallium), urethane, dioxin-like chemicals, various steroids, sex hormones (including xenoestrogens and antiandrogenic pesticides), and trypan blue, an agent once used to treat mange. Chemical agents disturb intracellular chemistry; embryonic changes usually precede placental changes. Other teratogenic agents include polychlorinated biphenyls (PCBs), solvents (benzene), plastics like Bisphenol A (BPA), air pollution, secondhand smoke from any type of tobacco product, and radiation, or chemotherapy medicines

Testing of some agents has shown increases in the frequency of common malformations. For example, dioxin and similar chemicals have been observed to increase cleft palate and hydronephrosis (a swelling of the kidneys caused by obstructed urine flow) in mice. A minimum of two species of animals, studied at a minimum of three dose levels, is essential for teratogenic testing. Strong teratogenic agents usually produce similar malformations in different species. Agents that produce demonstrable congenital anomalies in animals, especially in higher primates such as baboons, are presumed capable of producing congenital anomalies in a human fetus.

Prenatal exposure to ionizing radiation is another environmental factor known to cause congenital anomalies. For this reason, patients must disclose pregnancies to radiologic technicians before X-ray sessions so that the technician can minimize risks. Modern X-ray technology involves a very low exposure risk for the fetus; most problems result from accidental exposure or from necessary therapy. Exposure to large, fluctuating electromagnetic fields (EMFs) was previously suspected as a cause of environmental congenital anomalies. Speculation that high-voltage electric power transmission lines might cause environmental congenital anomalies or childhood cancer led to many epidemiological studies using small mammals; however, animal studies conducted over many years did not establish any link between high-voltage lines and congenital anomalies. Studies into the genotoxic potential (ability to alter genetic material) of EMFs have been conducted with bacteria, fruit flies, and mice. Although some cell research has suggested that EMF exposure may negatively affect the ability of cells to repair normal damage to genetic material, most evidence has suggested that EMF exposure is not genotoxic.

Research also indicates that exposure to bisphenol A (BPA), a chemical found in some plastics, contributes to developmental problems. Scientists have also linked PCBs and industrial solvents like benzene to heart and neural tube defects.

March of Dimes recommends avoiding eating fish that are known to contain high levels of mercury during pregnancy, including king mackerel, swordfish, tilefish, and shark.

Examples

Clusters of environmental congenital anomalies within human populations sometimes arise as a result of exposure of multiple persons to a release of a teratogenic agent, especially when the food chain is contaminated. When consumed during pregnancy, organic mercury is a potent teratogen. The best-known widespread occurrence of organic mercury poisoning took place in the 1950s and early 1960s in Japan’s Minamata Bay, where industrial effluents containing high levels of mercury were pumped into the ocean for many years. This mercury was assimilated into seafood consumed by the local population, resulting in many cases of congenital Minamata disease.

In contrast to the environmental health problems at Minamata Bay, which took years to emerge, damage to human health was immediately apparent in Bhopal, India, after the catastrophic December 1984 industrial accident that released a lethal cloud of methyl isocyanate gas over a crowded shantytown. Some pregnancies were spontaneously aborted upon exposure to the gas. A 1987 study found that, of a sample of 865 surviving pregnant individuals who lived within a kilometer (0.6 mile) of the accident site when the incident occurred, only 57 percent gave birth to live children. Of those babies, 14 percent died within a month of delivery, an infant mortality rate about five times greater than what was common in the community before the accident. Many were born with severe developmental conditions or congenital anomalies. In the decades after the release, congenital anomalies were common in children born to individuals exposed to the gas, including cleft palate, joined or extra fingers, developmental delays, and mental problems. Soil and groundwater contamination from chemicals abandoned at the industrial site continues to poison area residents, giving rise to still more congenital anomalies.

Use of chemical agents during wartime is also associated with widespread congenital anomalies. Birth Defect Research for Children has collected data since 1990 concerning an elevated incidence of congenital anomalies and developmental disabilities in the children of US veterans of the Vietnam War. Heavy use of the dioxin-tainted defoliant Agent Orange in Vietnam is associated with a suite of deformities and ailments among the children of veterans. These include spina bifida; oral clefts; learning, attention, and behavioral disorders; and increased susceptibility to chronic childhood infections and to cancers later in life. Vietnamese researchers have found that, in comparison with background levels in their country, rates of congenital anomalies are four times higher in areas that were sprayed with Agent Orange during the war.

In 2016, officials at the World Health Organization (WHO) issued a public health emergency in response to the Zika virus, a mosquito-borne illness that could cause congenital anomalies if contracted during a pregnancy. The main concern caused by the virus was microcephaly, a condition in which a child is born with a smaller head and an underdeveloped brain. Although WHO lifted the emergency declaration by the end of 2016, the Zika virus continued to be an issue in some locations into the 2020s.


Bibliography

"About Us." Birth Defect Research for Children, birthdefects.org/about-us. Accessed 16 Sept. 2025.

"Birth Defects and Your Baby." March of Dimes, Dec. 2024, www.marchofdimes.org/find-support/topics/planning-baby/birth-defects-and-your-baby. Accessed 16 Sept. 2025.

Duan, Junchao, et al. “Global and Regional Burden of Congenital Birth Defects, 1990-2021: Persistent Healthcare Disparities and Emerging Challenges from Non-Fatal Health Burden.” BMJ Public Health, vol. 3, no. 1, 2025, doi:10.1136/bmjph-2024-001608. Accessed 16 Sept. 2025.

Hansen, Deborah Kay, and Barbara D. Abbott, editors. Developmental Toxicology. 3rd ed., Informa Healthcare, 2009.

Kofoed, Ane Bungum, et al. “Maternal Exposure to Airborne Polychlorinated Biphenyls (PCBs) and Risk of Adverse Birth Outcomes.” European Journal of Epidemiology, vol. 36, no. 8, 2021, pp. 861–72, doi:10.1007/s10654-021-00793-x. Accessed 16 Sept. 2025.

Lee, Kyung Shin, et al. “Environmental and Genetic Risk Factors of Congenital Anomalies: An Umbrella Review of Systematic Reviews and Meta-Analyses.” Journal of Korean Medical Science, vol. 36, no. 28, 2021, p. e183, doi:10.3346/jkms.2021.36.e183. Accessed 16 Sept. 2025.

Lipinski, Robert J., and Robert S. Krauss. Gene-Environment Interactions in Birth Defects and Developmental Disorders. Academic Press, 2023.

Liu, Hanjun, et al. “Emerging Trends and Cross-Country Health Inequalities in Congenital Birth Defects: Insights from the GBD 2021 Study.” International Journal for Equity in Health, vol. 24, no. 1, 2025, doi:10.1186/s12939-025-02412-7. Accessed 16 Sept. 2025.

Moore, Keith L., and T. V. N. Persaud. Before We Are Born: Essentials of Embryology and Birth Defects. 11th ed., Saunders/Elsevier, 2024.

Reshi, Mohd Salim, et al. Environmental Toxicology: Concepts and Principles. Jenny Stanford Publishing, 2025.

Sauvé, Sébastien. “Toxicology, Environmental Chemistry, Ecotoxicology, and One Health: Definitions and Paths for Future Research.” Frontiers in Environmental Science, vol. 12, 2024, doi:10.3389/fenvs.2024.1303705. Accessed 16 Sept. 2025.

Schardein, James L. Chemically Induced Birth Defects. 3rd ed., Marcel Dekker, 2000.

Shilpa S. Shetty, et al. “Environmental Pollutants and Their Effects on Human Health.” Heliyon, vol. 9, no. 9, 2023, p. e19496. doi:10.1016/j.heliyon.2023.e19496. Accessed 16 Sept. 2025.

"Zika Virus." World Health Organization, 8 Dec. 2022, www.who.int/news-room/fact-sheets/detail/zika-virus. Accessed 16 Sept. 2025.

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