Teratogens: Examples, Risks, and Prevention - Verywell Health

Examples of teratogens—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.

Jamie Grill / Getty Images

What Is a Teratogen?

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.

Examples of Teratogens

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:

• Thalidomide (leprosy and lupus medication)
• Isotretinoin (lupus and acne medication)
• Valproic acid (an antiepileptic drug)
• Methotrexate (treatment for psoriasis, rheumatoid arthritis, and cancer)
• Mycophenolate mofetil (used in transplant recipients)
• Vitamin A (too much or too little)
• Antimicrobial medications like chloramphenicol, tetracyclines, fluoroquinolones
• Warfarin and other anticoagulants categorized as coumarin derivates
• Potentially, propylthiouracil (PTU), methimazole (MMI), and carbimazole (hyperthyroidism medications)

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.

One particular teratogen example used in the treatment of leprosy and lupus is thalidomide. Thalidomide is a category X medication, meaning it poses a substantial risk of birth defects. The risks can be severe and cause death in the unborn baby—even from one dose. Don't take thalidomide if you're pregnant or think you could be. Talk to your healthcare provider about alternatives if you are pregnant or are planning to become pregnant.

Another category of teratogens includes alcohol, tobacco, and recreational drugs. These teratogens are best avoided during pregnancy:

• Recreational drugs such as cocaine, marijuana, amphetamines, ecstasy, and heroin
• Alcohol
• Tobacco

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:

• Toxoplasmosis: a parasitic infection most often associated with kitty litter
• Others: like Treponema pallidum, a bacterial infection that causes syphilis
• Rubella: a viral infection that is also known as German measles
• Cytomegalovirus (CMV): a common viral infection
• Herpes simplex virus: a virus that presents as sores on or in the mouth (HSV1), or sores in or around the genitals (HSV2)

In addition to TORCH, some other infections that are teratogenic include:

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 called electric 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.

Hyperthermia (abnormally high body temperature) can be teratogenic during pregnancy. Hyperthermia can be caused by things like exercise, hot tubs, and saunas.

Mitigating hyperthermia risk involves ensuring that your core body temperature does not rise above 102.2 F (39 C). Research has found moderate exercise (defined as up to 35 minutes at 50% to 70% of maximum heart rate) and limited exposure to hot baths and saunas to be safe.

Environmental Toxins

Toxic metals and chemicals can pose risks to a developing fetus. Some examples of environmental toxins include:

• Mercury
• Lead
• Polychlorinated and polybrominated biphenyls (PCBs)

Mercury exposure most commonly happens through eating contaminated fish and getting amalgam (mercury) dental fillings. If you need dental work done while pregnant, talk to your dentist about using non-mercury filling material.

Limit mercury exposure by avoiding certain fish that have high concentrations of mercury. King mackerel, marlin, orange roughy, shark, swordfish, tilefish, tuna, and bigeye are all fish that are highest in mercury.

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 exposure can 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.

You can limit your exposure to household lead by keeping painted surfaces in good shape, cleaning lead dust with a wet paper towel, using only certified lead professionals for renovations, wiping or removing shoes before entering your home, and having lead water lines replaced.

PCBs are found in fluorescent lights, fish caught in contaminated waters, older TVs and appliances, and soil around contaminated waste sites. You can limit your exposure by not eating fish caught in contaminated water, updating older appliances, and staying out of the soil near contaminated waste sites.

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 special PKU 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 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 four weeks 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 like fetal alcohol syndrome.

How Common Are Birth Defects From Teratogens?

About 4% to 5% of birth defects are caused by exposure to a teratogen. It is important to avoid teratogens throughout your pregnancy, especially in the first trimester when the risk to a fetus is highest.

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:

• Avoid alcohol, recreational drugs, and cigarettes while pregnant.
• Use good hand hygiene to avoid illnesses.
• Limit or avoid hot tubs and saunas.
• Manage any pre-existing health conditions.
• Discuss medications and vaccinations with your healthcare provider.

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.

Adblock test (Why?)