Teratogens

What Are Teratogens?

Teratogens are substances that cause birth disorders during pregnancy. A teratogen is anything you’re exposed to or ingest during pregnancy that’s known to harm a fetus or embryo. Teratogens can also increase your risk for miscarriage, preterm labor or stillbirth. Examples include certain medicines, recreational drugs, chemicals, infections and toxins.

The effects of teratogens during pregnancy depend on factors like:

• The type of substance
• How long you were exposed
• How much you were exposed to
• How many weeks pregnant you were when exposed
• Genetics

Not every exposure during pregnancy is harmful, and accidental exposures can happen. Knowing which substances may cause harm can help you make decisions that support a healthy pregnancy. If you have questions about a medicine, supplement, chemical or other toxin, talk with your healthcare provider. They can help you understand any possible risks and what to avoid.

What are examples of teratogens?

Teratogens are substances that can harm the fetus during pregnancy. They include substances you put into your body as well as things you’re exposed to in your environment.

Alcohol, tobacco and recreational drugs

Some of the most common teratogens include alcohol, tobacco and recreational drugs:

• Alcohol: Drinking alcohol can cause fetal alcohol syndrome. This may lead to lifelong physical, behavioral and learning problems. Experts recommend avoiding alcohol during pregnancy.
• Tobacco: Smoking tobacco products, like cigarettes, during pregnancy increases the risk of fetal growth restriction, miscarriage and premature birth. It can also affect lung and brain development.
• Recreational drugs: Using drugs like cocaine, heroin, marijuana or methamphetamines during pregnancy can cause low birth weight, heart problems and neonatal abstinence syndrome. This is when a baby goes through drug withdrawal after birth. Sharing needles can also cause infection.

Medications

Certain over-the-counter (OTC) and prescription medications are considered teratogens. That’s why it’s important to tell your healthcare provider about any medications you take. And read the labels before taking any medications or supplements. When in doubt, call your healthcare provider. It’s best to avoid the substance until you hear from them.

Examples of teratogenic medications are:

• Antiepileptic drugs (AEDs)
• Antimicrobials
• Blood thinners
• Antithyroid medications
• Vitamin A (a common ingredient in skincare products)
• Hormonal medication

If you take a prescription medicine, don’t stop taking it without talking to your provider first. Some medicines can affect pregnancy, but stopping a medicine suddenly may be dangerous for you. Your provider can help you decide what’s best.

How is medication rated for safety during pregnancy?

Healthcare providers use the Pregnancy and Lactation Labeling Rule (PLLR) to understand the possible risks and benefits of medications during pregnancy and breastfeeding. With this information in mind, your provider makes a decision based on your unique health needs and situation. The PLLR replaced the older letter category system (A, B, C, D and X) because those categories didn’t provide enough detail. You may still hear or see the letter categories, though.

Infections and viruses

Infections from viruses, parasites and bacteria can cause serious problems during pregnancy. The acronym TORCH helps to classify some of these infections:

• Toxoplasmosis (an infection that spreads through cat poop)
• Other infections, like group B streptococcus, listeria, candida and sexually transmitted infections (STIs)
• Rubella
• Cytomegalovirus (CMV)
• Herpes
• Syphilis

Other infections and viruses that can cause pregnancy complications are:

• Chickenpox and shingles
• Hepatitis B, Hepatitis C and other types of viral hepatitis
• HIV
• Fifth disease

Environmental toxins, chemicals or other physical agents

Certain toxins, chemicals and other physical agents may cause congenital abnormalities. Some examples are:

• Radiation exposure or chemotherapy
• Hot tubs, saunas or other heat sources that raise your body temperature
• Mercury (found in certain types of fish)
• Lead (commonly found in paint and pipes in older homes)
• Toxic chemicals or heavy metals found in the workplace or manufacturing facilities

Health conditions

Certain chronic illnesses can increase the fetus’s risk of birth disorders. Some examples are diabetes, thyroid conditions and autoimmune diseases, like lupus or rheumatoid arthritis.

In most cases, the increased risk is related to the condition not being well-managed or the medications needed to treat it. Your healthcare provider can help you manage your condition and choose treatments that are safest during pregnancy.

What birth defects do teratogens cause?

Teratogens cause many known congenital disorders. Some of the most common abnormalities are:

• Brain or spinal cord disorders, like spina bifida
• Missing or unusually formed body parts
• Cleft lip and palate
• Learning problems or problems with the brain and nervous system
• Cardiovascular issues or heart conditions

When is teratogen exposure the worst during pregnancy?

Exposure to teratogens is harmful no matter what point you’re at in pregnancy. But the risk is slightly higher during the first eight weeks of pregnancy. This is because many organs and systems are developing, making the fetus more sensitive to the harmful effects of teratogens.

How can you avoid teratogens during pregnancy?

The best way to avoid teratogens is to plan for pregnancy, if possible. Planning for pregnancy gives you time to manage chronic conditions or make lifestyle changes, like quitting smoking.

But this isn’t always possible. Once you’re pregnant, some things you can do to lower your risk of teratogen exposure are:

• Talk with your healthcare provider about any medications you’re taking.
• Avoid cigarettes, alcohol and recreational drugs.
• Don’t take any supplements or medications (OTC or prescription) without checking with your healthcare provider first.
• Avoid cleaning litter boxes.
• Avoid hot tubs, saunas and anything that raises your body temperature.
• Don’t eat tuna, swordfish and other fish high in mercury.
• Talk with your supervisor or human resources about harmful chemicals in your workplace.

It’s important to have open and honest conversations with your obstetrician during pregnancy. This includes being truthful about alcohol or drug use. They want to support you and make sure your pregnancy is healthy.