8.5.3: Teratogens

Learning Objectives

1. Define teratogens and explain their role in prenatal development.
2. Identify key factors that influence teratogenic impact, including timing, dosage, genetics, and fetal sex.
3. Describe major categories of teratogens (e.g., infections, drugs, environmental toxins).
4. Identify common examples of teratogens.

Teratogens

Good prenatal care is essential to protect against maternal and fetal/infant mortality and birth complications. The embryo and fetus are most at risk for some of the most severe problems during the first three months of development. Unfortunately, this is a time at which many mothers are unaware that they are pregnant. Today, we are aware of many factors that can compromise the health of the developing child. The study of factors that contribute to birth defects is called teratology. Teratogens (pronounced tara-tow-genz) are environmental factors that can contribute to birth defects, and include some maternal diseases, pollutants, drugs, and alcohol.

Factors Influencing Prenatal Risks

Several considerations are involved in determining the type and amount of damage that may result from exposure to a particular teratogen (Berger, 2005). These include:

• The timing of exposure: Structures in the body are most vulnerable to severe damage when they are forming. If a substance is introduced during a particular structure's critical period (time of development), the damage to that structure may be greater. For example, the ears and arms reach their critical periods at about 6 weeks after conception. If an embryo is exposed to certain substances during this period, the arms and ears may be malformed. (see figure below)
• The amount of exposure: Some substances are not harmful unless the amounts reach a certain level. The critical level depends in part on the size and metabolism of the mother.
• The number of teratogens: Fetuses exposed to multiple teratogens typically have more problems than those exposed to only one.
• Genetics: The genetic makeup also plays a role in the impact a particular teratogen may have on the child. This is suggested by fraternal twins exposed to the same prenatal environment, but they do not experience the same teratogenic effects. The genetic makeup of the mother can also have an effect; some mothers may be more resistant to teratogenic effects than others.
• Being male or female: Males are more likely to experience damage due to teratogens than are females. It is believed that the Y chromosome, which contains fewer genes than the X, may have an impact. ³¹

Figure \(\PageIndex{1}\): The development of an embryo into a fetus. Image by Laura Overstreet is licensed under CC BY-NC-SA 3.0

Categories of Teratogens

Physical teratogens

These could be saunas, hot tubs, or fevers that raise a pregnant woman's body temperature to 102 degrees Fahrenheit or higher. This is associated with neural tube defects, spontaneous abortions, and various cardiovascular abnormalities. Physical teratogens may also include exposure to radiation.

Metabolic conditions affecting pregnant females

Metabolic conditions are abnormalities in the chemical process of producing energy from food, and thereby affect the development and function of the body. If a pregnant woman is malnourished, then her fetus likely lacks the nutrients essential for its development. These include: malnutrition, diabetes, and thyroid disorders.

Infections

Different maternal infections, including rubella virus, herpes simplex virus, and syphilis, can cause congenital abnormalities in fetuses.

Table \(\PageIndex{1}\): Maternal Infections as Teratogens

Teratogen	Potential Effects
Rubella	Congenital infection (becoming infected while in the womb) can damage the development of the eyes, ears, heart, and brain and result in deafness.^47
Zika	Congenital infection can cause microcephaly and other severe brain abnormalities. ^48
Varicella (chicken pox)	Congenital infection can cause a severe form of the infection affecting the eyes, limbs, skin, and central nervous system. ^49
Sexually transmitted infections	Infections such as HIV, gonorrhea, syphilis, and chlamydia can be passed from the mother during pregnancy and/or delivery. ^50
Listeria	Pregnant women are more susceptible to this foodborne illness. Congenital infection can cause miscarriage, stillbirth, premature labor, and neonatal sepsis. ^51

Drugs and chemicals

When pregnant females ingest or absorb these, they may cause a variety of different effects based on the specific agent, amount of exposure, and timing. This category includes: radiation, heavy metals (including lead), insecticides and herbicides, prescription and over-the-counter drugs, illicit and recreational drugs, alcohol, cigarettes, nicotine, caffeine, and even some vitamins. ³³

While there are many potential teratogens, the following tables examine the effects of various types of teratogens. The risks of exposure vary based on lifestyle and health. The effects may vary greatly depending on the factors mentioned previously. Protection and prevention will vary based on the method of exposure.

Table \(\PageIndex{2}\): Drugs as Teratogens

Teratogen	Potential Effects
Caffeine	Moderate amounts of caffeine (200 mg, equivalent to approximately 12 ounces of coffee) appear to be safe during pregnancy. Some studies have shown a link between higher amounts of caffeine and miscarriage and preterm birth.^34
Tobacco	Tobacco use has been associated with low birth weight, placenta previa, preterm delivery, fetal growth restriction, sudden infant death syndrome, cleft lip or palate, and later health problems (such as high blood pressure and diabetes). ^35
Alcohol	There is no safe amount of alcohol a woman can drink while pregnant. Alcohol can slow down the baby's growth, affect the baby's brain, and cause birth defects, and may result in fetal alcohol spectrum disorder (FASD). The effects can be mild to severe. Children born with a severe form of FASD can have abnormal facial features, severe learning disabilities, behavioral problems, and other problems.^36
Cocaine	Cocaine use has connected with low birth weight, stillbirths, spontaneous abortion, placental abruption, premature birth, miscarriage, and neonatal abstinence syndrome (fetal addiction leads the newborn to experiences withdrawal).^37
Marijuana	No amount of marijuana has been proven safe to use during pregnancy. Heavy use has been associated with brain damage, premature birth, and stillbirth.^38
Heroin	Using heroin during pregnancy can cause birth defects, placental abruption, premature birth, low birthweight, neonatal abstinence syndrome, stillbirth, and sudden infant death syndrome.^39
Over-the-Counter (OTC) medication	Some OTC medications are safe to use during pregnancy, and others may cause health problems during pregnancy. Pregnant women should consult their health care provider before using OTC medications.^40
Prescription drugs	Some prescription drugs can cause birth defects that change the shape or function of one or more parts of the body, which can affect overall health. Pregnant women should consult their health care provider before discontinuing or starting new medications.^41
Herbal or dietary supplements	Except for certain vitamins, little is known about the use of herbal or dietary supplements during pregnancy. Most often, there are no good studies to show if the herb can cause harm to you or your baby. Also, some herbs that are safe when used in small amounts as food might be harmful when used in large amounts as medicines.^42

Environmental pollutants

Environmental teratogens are substances or factors in the environment that can interfere with fetal development during pregnancy.

Table \(\PageIndex{3}\): Environmental Teratogens

Teratogen	Potential Effects
Lead	Exposure to high levels of lead before and during pregnancy can lead to high blood pressure, problems with fetal brain and nervous system development, premature birth, low birthweight, and miscarriage.^43
Mercury	Exposure to mercury in the womb can cause brain damage and hearing and vision problems^.44
Radiation	Exposure to radiation during pregnancy (especially between 2 and 18 weeks of pregnancy) can slow growth, cause birth defects, affect brain development, cause cancer, and cause miscarriage.^45
Solvents	These chemicals include degreasers, paint thinners, stain and varnish removers, paints, and more Maternal inhalation of solvents can cause fetal exposure than may cause miscarriage, slow fetal growth, premature birth, and birth defects.^46

Figure \(\PageIndex{2}\): A USDA employee pouring hazardous chemicals into a storage container. Image by USDA is in the public domain.

Table \(\PageIndex{4}\): Teratogens from Animals/Pets

Teratogen	Potential Effects
Toxoplasmosis	This parasite can be transmitted through cat feces and undercooked meat, especially pork, lamb, or deer meat. If the fetus is infected, it can cause miscarriage, stillbirth, hydrocephalus, macro or microcephalus, vision issues, and damage to the nervous system.^52
Lymphocytic choriomeningitis	Rodents, including mice, hamsters, and guinea pigs carry this virus. If an infected mother passes it to her fetus, it can cause issues with brain development, long-term neurological and/or visual impairment, and higher mortality rates after birth.^53

References, Contributors and Attributions

Berger, K. S. (2005). The developing person through the life span (6th ed.). New York: Worth.

34. Staying healthy and safe by OWH is in the public domain

35. Chapter 3: Prenatal Development – Environmental Risks references Psyc 200 Lifespan Psychology by Laura Overstreet, which is licensed under CC BY 4.0;

Staying healthy and safe by OWH is in the public domain

36. Staying healthy and safe by OWH is in the public domain

37. Chapter 3: Prenatal Development – Environmental Risks references Psyc 200 Lifespan Psychology by Laura Overstreet, which is licensed under CC BY 4.0;

Prescription drugs, over-the-counter drugs, supplements and herbal products (n.d.). Retrieved from: https://www.marchofdimes.org/pregnancy/prescription-drugs-over-the-counter-drugs-supplements-and-herbal-products.aspx

38. Chapter 3: Prenatal Development – Environmental Risks references Psyc 200 Lifespan Psychology by Laura Overstreet, which is licensed under CC BY 4.0;

Prescription drugs, over-the-counter drugs, supplements and herbal products (n.d.). Retrieved from: https://www.marchofdimes.org/pregnancy/prescription-drugs-over-the-counter-drugs-supplements-and-herbal-products.aspx

39. Prescription drugs, over-the-counter drugs, supplements and herbal products (n.d.). Retrieved from: https://www.marchofdimes.org/pregnancy/prescription-drugs-over-the-counter-drugs-supplements-and-herbal-products.aspx

40. Prescription drugs, over-the-counter drugs, supplements and herbal products (n.d.). Retrieved from: https://www.marchofdimes.org/pregnancy/prescription-drugs-over-the-counter-drugs-supplements-and-herbal-products.aspx

41. Prescription drugs, over-the-counter drugs, supplements and herbal products (n.d.). Retrieved from: https://www.marchofdimes.org/pregnancy/prescription-drugs-over-the-counter-drugs-supplements-and-herbal-products.aspx

42. Chapter 3: Prenatal Development – Environmental Risks references Psyc 200 Lifespan Psychology by Laura Overstreet, which is licensed under CC BY 4.0

43. Prescription drugs, over-the-counter drugs, supplements and herbal products (n.d.). Retrieved from: https://www.marchofdimes.org/pregnancy/prescription-drugs-over-the-counter-drugs-supplements-and-herbal-products.aspx

44. Prescription drugs, over-the-counter drugs, supplements and herbal products (n.d.). Retrieved from: https://www.marchofdimes.org/pregnancy/prescription-drugs-over-the-counter-drugs-supplements-and-herbal-products.aspx

45. Prescription drugs, over-the-counter drugs, supplements and herbal products (n.d.). Retrieved from: https://www.marchofdimes.org/pregnancy/prescription-drugs-over-the-counter-drugs-supplements-and-herbal-products.aspx

46. Prescription drugs, over-the-counter drugs, supplements and herbal products (n.d.). Retrieved from: https://www.marchofdimes.org/pregnancy/prescription-drugs-over-the-counter-drugs-supplements-and-herbal-products.aspx

47. Chapter 3: Prenatal Development – Environmental Risks references Psyc 200 Lifespan Psychology by Laura Overstreet, which is licensed under CC BY 4.0

48. Protocols on prenatal care for pregnant women with Zika infection and children with microcephaly: nutritional approach by Rachel de Sá Barreto Luna Callou Cruz, Malaquias Batista Filho, Maria de Fátima Costa Caminha, and Edvaldo da Silva Souza is licensed under CC BY 4.0

49. Congenital Varicella syndrome by WikiDoc is licensed under CC BY-SA 3.0

50. Chapter 3: Prenatal Development – Environmental Risks references Psyc 200 Lifespan Psychology by Laura Overstreet, which is licensed under CC BY 4.0

51. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2860824/

52. Prescription drugs, over-the-counter drugs, supplements and herbal products (n.d.). Retrieved from: https://www.marchofdimes.org/pregnancy/prescription-drugs-over-the-counter-drugs-supplements-and-herbal-products.aspx

53. Prescription drugs, over-the-counter drugs, supplements and herbal products (n.d.). Retrieved from: https://www.marchofdimes.org/pregnancy/prescription-drugs-over-the-counter-drugs-supplements-and-herbal-products.aspx