Table of ContentsView AllTable of ContentsWhat Is a Teratogen?Examples of TeratogensExposure and RisksPrevention
Table of ContentsView All
View All
Table of Contents
What Is a Teratogen?
Examples of Teratogens
Exposure and Risks
Prevention
Examples ofteratogens—agents that cause birth defects—are more numerous than you may realize. During pregnancy, exposure to certain chemicals, infections, and drugs may increase the risk that a person will miscarry or that the embryo or fetus could have a developmental abnormality.
Alcohol and smoking are two common teratogens. Exposure to either of them can lead to developmental anomalies, miscarriage, stillbirth,preterm labor, and a variety of other pregnancy complications.
This article explains what a teratogen is using numerous examples of teratogens, including drugs, infections, physical agents, environmental toxins, and maternal health conditions. It also discusses teratogen exposure and risks and offers prevention tips.
A teratogen is a substance that may lead to birth defects in an embryo or fetus. The impact of teratogens on pregnancy or a fetus depends on several factors. The timing and length of exposure, the stage of pregnancy when the exposure happened, genetic factors influencing susceptibility, and the type of agent of exposure all contribute to the risk.
Teratogens can be grouped into one of several categories. These include drugs, infections, physical agents, environmental toxins, and maternal health conditions.
Drugs
Many pregnant people take prescription medications and over-the-counter (OTC) medications. Not all medications pose the same hazards, but it’s important to be aware of the medications that are known teratogens.
The U.S. Food and Drug Administration (FDA) has a rating system for medication risks during pregnancy. The FDA’s five risk categories are A, B, C, D, and X. Category A medication has been found to pose no risk to the fetus during pregnancy and is the safest category.
The risk rises successively in categories B, C, and D. Category X means animal or human studies have shown these substances can lead to developmental abnormalities in the fetus. Category X medications are to be avoided during pregnancy because the risks outweigh the benefits.
The following medications are examples of known teratogens:
Some OTC medications may contain teratogens as well. Read the labels to learn about risks to pregnant people, and talk to your healthcare provider about any medications you are considering taking.
Another category of teratogens includes alcohol, tobacco, and recreational drugs. These teratogens are best avoided during pregnancy:
Infections
Not all infections affect a developing fetus and pregnancy in the same way. Pregnant people often encounter the common cold and some milder infections without incident. However, some illnesses have a greater potential to impact a pregnancy.
TORCH is an acronym that can help you remember the most common teratogenic viruses, parasites, and bacteria. They include:
In addition to TORCH, some other infections that are teratogenic include:
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Physical Agents
Exposure to certain necessary medical interventions, workplace hazards, or heat can pose a risk to fetuses as well. Radiation exposure and heat are both considered physical teratogens.
Radiation, also calledelectric and magnetic fields, is either ionizing or non-ionizing. Examples of non-ionizing radiation are microwaves, ultrasound, radio frequencies, computers, cell phones, and power lines. Studies have not found that these pose a significant risk during pregnancy.
Ionizing radiation includes things like X-rays, gamma rays, and sunlight. These can be harmful. The risk of exposure to ionizing radiation varies, depending on the dose of exposure and pregnancy stage. The highest risk is associated with higher doses and exposure in the first trimester.
Environmental Toxins
Toxic metals and chemicals can pose risks to a developing fetus. Some examples of environmental toxins include:
The “Dietary Guidelines for Americans 2020–2025” recommends that pregnant people eat 8 to 12 ounces of seafood per week from choices that are low in methylmercury.
Lead exposurecan happen from contact with lead in the air, soil, water, and household dust. Paint used in homes before 1978 often contained lead, and many older water pipes are made of lead.
Maternal Health Conditions
Some maternal health conditions pose teratogenic risks. Chronic health conditions that can impact a developing fetus include:
Research suggests that maternal autoimmune disease may be associated with some birth defects, but not with most of them.Risks associated with diabetes include birth defects of the spine, brain, limbs, and heart.
PKU is a genetic disorder that is passed down from parents to children. It is managed through a specialPKU diet. Unmanaged during pregnancy, PKU can lead to low birth weight, intellectual disabilities, heart defects, and other birth defects.
If you have a pre-existing health condition, it is very important to maintain treatment to limit the teratogenic risk during pregnancy. Talk to your healthcare provider about concerns you have about your health conditions and treatment options.
Limit Your RiskIf you’re pregnant, avoid medications when you can and take the lowest dose possible of those you must take. If you need X-rays or other medical tests, be sure to inform your healthcare professional that you are pregnant. Controlling health conditions can help to limit the teratogenic risk.
Limit Your Risk
If you’re pregnant, avoid medications when you can and take the lowest dose possible of those you must take. If you need X-rays or other medical tests, be sure to inform your healthcare professional that you are pregnant. Controlling health conditions can help to limit the teratogenic risk.
Teratogen Exposure and Risks
The risk of teratogens to a developing fetus is often early in the pregnancy—usually the first trimester and often before implantation. Of course, the impact also depends on the level of exposure.
If a teratogen has the ability to affect the development of the neural tube, the exposure would need to occur before the time the neural tube closes, which is around three to fourweeks of pregnancy. Some organ systems are susceptible throughout pregnancy, though.
The central nervous system, for example, can be impacted throughout an entire pregnancy. Alcohol is an example of a teratogen that can impact a developing fetus at any time during pregnancy, leading to conditions likefetal alcohol syndrome.
How Common Are Birth Defects From Teratogens?
Preventing Teratogen Risks
Sometimes it can be difficult to avoid teratogens altogether, especially if you have a pre-existing health condition or require medication. Still, there are some things you can do to limit your exposure:
Summary
It can be scary to think about bad outcomes and birth defects while you are pregnant. The good news is that exposure to teratogens only accounts for a very small percentage of birth defects. Most of the time, people are able to avoid the things that can negatively impact fetal development.
Even if you can’t avoid teratogens completely, there are things you can do to limit the risk to your developing fetus. Having proactive and open communication with your healthcare provider can help you manage any ongoing medical issues in a way that is safer for your pregnancy and your fetus.
Most of the time, people with health conditions and those who require medication go on to have full-term pregnancies and healthy babies.
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19 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Chemical Hazards Emergency Medical Management.FDA pregnancy categories.Centers for Disease Control and Prevention.CDC grand rounds: understanding the causes of major birth defects — steps to prevention.Bastos Maia S, Rolland Souza AS, Costa Caminha MF, Lins da Silva S, Callou Cruz RSBL, Carvalho Dos Santos C, Batista Filho M.Vitamin A and pregnancy: a narrative review.Nutrients. 2019;11(3):681. doi:10.3390/nu11030681Romeo AN, Običan SG.Teratogen update: antithyroid medications.Birth Defects Res. 2020;112(15):1150-1170. doi:10.1002/bdr2.1771U.S. Food and Drug Administration.Medicine and pregnancy.U.S. Food and Drug Administration.Thalomid® capsules.Adams Waldorf K, McAdams R.Influence of infection during pregnancy on fetal development.Reproduction. 2013;146(5):R151-R162. doi:10.1530/rep-13-0232Health Physics Society.Pregnancy and radiation exposure.Jain C.ACOG committee opinion no. 723: guidelines for diagnostic imaging during pregnancy and lactation.Obstet Gynecol. 2019;133(1):186. doi:10.1097/AOG.0000000000003049Ravanelli N, Casasola W, English T, Edwards K, Jay O.Heat stress and fetal risk. Environmental limits for exercise and passive heat stress during pregnancy: a systematic review with best evidence synthesis.Br J Sports Med. 2018;53(13):799-805. doi:10.1136/bjsports-2017-097914U.S. Food and Drug Administration.FDA issues recommendations for certain high-risk groups regarding mercury-containing dental amalgam.U.S. Department of Agriculture.Dietary guidelines for Americans.U.S. Environmental Protection Agency.Protect your family from sources of lead.U.S. Environmental Protection Agency.Learn about polychlorinated biphenyls.Howley M, Browne M, Van Zutphen A et al.Maternal autoimmune disease and birth defects in the National Birth Defects Prevention Study.Birth Defects Res A Clin Mol Teratol. 2016;106(11):950-962. doi:10.1002/bdra.23527Centers for Disease Control and Prevention.Birth defects.March of Dimes.Maternal PKU.Children’s Wisconsin.Teratogens.Centers for Disease Control and Prevention.Preventing birth defects.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Chemical Hazards Emergency Medical Management.FDA pregnancy categories.Centers for Disease Control and Prevention.CDC grand rounds: understanding the causes of major birth defects — steps to prevention.Bastos Maia S, Rolland Souza AS, Costa Caminha MF, Lins da Silva S, Callou Cruz RSBL, Carvalho Dos Santos C, Batista Filho M.Vitamin A and pregnancy: a narrative review.Nutrients. 2019;11(3):681. doi:10.3390/nu11030681Romeo AN, Običan SG.Teratogen update: antithyroid medications.Birth Defects Res. 2020;112(15):1150-1170. doi:10.1002/bdr2.1771U.S. Food and Drug Administration.Medicine and pregnancy.U.S. Food and Drug Administration.Thalomid® capsules.Adams Waldorf K, McAdams R.Influence of infection during pregnancy on fetal development.Reproduction. 2013;146(5):R151-R162. doi:10.1530/rep-13-0232Health Physics Society.Pregnancy and radiation exposure.Jain C.ACOG committee opinion no. 723: guidelines for diagnostic imaging during pregnancy and lactation.Obstet Gynecol. 2019;133(1):186. doi:10.1097/AOG.0000000000003049Ravanelli N, Casasola W, English T, Edwards K, Jay O.Heat stress and fetal risk. Environmental limits for exercise and passive heat stress during pregnancy: a systematic review with best evidence synthesis.Br J Sports Med. 2018;53(13):799-805. doi:10.1136/bjsports-2017-097914U.S. Food and Drug Administration.FDA issues recommendations for certain high-risk groups regarding mercury-containing dental amalgam.U.S. Department of Agriculture.Dietary guidelines for Americans.U.S. Environmental Protection Agency.Protect your family from sources of lead.U.S. Environmental Protection Agency.Learn about polychlorinated biphenyls.Howley M, Browne M, Van Zutphen A et al.Maternal autoimmune disease and birth defects in the National Birth Defects Prevention Study.Birth Defects Res A Clin Mol Teratol. 2016;106(11):950-962. doi:10.1002/bdra.23527Centers for Disease Control and Prevention.Birth defects.March of Dimes.Maternal PKU.Children’s Wisconsin.Teratogens.Centers for Disease Control and Prevention.Preventing birth defects.
Chemical Hazards Emergency Medical Management.FDA pregnancy categories.
Centers for Disease Control and Prevention.CDC grand rounds: understanding the causes of major birth defects — steps to prevention.
Bastos Maia S, Rolland Souza AS, Costa Caminha MF, Lins da Silva S, Callou Cruz RSBL, Carvalho Dos Santos C, Batista Filho M.Vitamin A and pregnancy: a narrative review.Nutrients. 2019;11(3):681. doi:10.3390/nu11030681
Romeo AN, Običan SG.Teratogen update: antithyroid medications.Birth Defects Res. 2020;112(15):1150-1170. doi:10.1002/bdr2.1771
U.S. Food and Drug Administration.Medicine and pregnancy.
U.S. Food and Drug Administration.Thalomid® capsules.
Adams Waldorf K, McAdams R.Influence of infection during pregnancy on fetal development.Reproduction. 2013;146(5):R151-R162. doi:10.1530/rep-13-0232
Health Physics Society.Pregnancy and radiation exposure.
Jain C.ACOG committee opinion no. 723: guidelines for diagnostic imaging during pregnancy and lactation.Obstet Gynecol. 2019;133(1):186. doi:10.1097/AOG.0000000000003049
Ravanelli N, Casasola W, English T, Edwards K, Jay O.Heat stress and fetal risk. Environmental limits for exercise and passive heat stress during pregnancy: a systematic review with best evidence synthesis.Br J Sports Med. 2018;53(13):799-805. doi:10.1136/bjsports-2017-097914
U.S. Food and Drug Administration.FDA issues recommendations for certain high-risk groups regarding mercury-containing dental amalgam.
U.S. Department of Agriculture.Dietary guidelines for Americans.
U.S. Environmental Protection Agency.Protect your family from sources of lead.
U.S. Environmental Protection Agency.Learn about polychlorinated biphenyls.
Howley M, Browne M, Van Zutphen A et al.Maternal autoimmune disease and birth defects in the National Birth Defects Prevention Study.Birth Defects Res A Clin Mol Teratol. 2016;106(11):950-962. doi:10.1002/bdra.23527
Centers for Disease Control and Prevention.Birth defects.
March of Dimes.Maternal PKU.
Children’s Wisconsin.Teratogens.
Centers for Disease Control and Prevention.Preventing birth defects.
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