2.7: Teratogens

Teratogens - Environmental Factors and Birth Defects

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 know many of the factors that can jeopardize the health of the developing child. The study of factors that contribute to birth defects is called teratology.

Factors influencing prenatal risks:

• Timing of the exposure: structures in the body are vulnerable to the most severe damage when they are in the process of forming. If a substance is introduced during a 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 a mother exposes the embryo to certain substances during this period, the arms and ears may be malformed.

• 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.

• Number of teratogens: Fetuses exposed to multiple teratogens typically have more problems than those exposed to only one.

• Genetics: genetic makeup also plays a role on the impact a teratogen might 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.

Fig. 2.7. Development of embryo into a fetus and stages at which it is vulnerable to developing major morphological abnormalities (first 8 weeks) and development of functional defect and minor morphological abnormalities, (8 weeks-birth).

Image Source: Heredity, Prenatal Development, and Birth: Teratogens. Lifespan Development. License: CC BY-NC-SA: Attribution-NonCommercial-ShareAlike.

Categories of Teratogens

Be aware of these common teratogens that can contribute to issues with embryonic and fetal development as well as birth defects and abnormalities.

Physical Teratogens

High temperatures are associated with neural tube defects (birth defects of the brain, spine or spinal cord), spontaneous abortions (miscarriage), various cardiovascular abnormalities (congenital heart disease, arrhythmias). Examples of causes of high temperatures include:

• saunas, hot tubs
• intense exercise
• radiation - x-rays, gamma rays
• infections that raise a pregnant woman's body temperature to 102 degrees Fahrenheit or higher.

Metabolic Conditions

Metabolic conditions are abnormalities in the chemical process of producing energy from food, and thereby affect the development and function of the body. For example, if a pregnant woman is malnourished then her fetus likely lacks the nutrients essential for its proper development which can result in anything from small birth weight to malformation of critical organs like the lungs, heart, or kidneys; and neurological issues like developmental delays, seizures, and intellectual disabilities. Examples of metabolic conditions are:

• malnutrition
• uncontrolled diabetes
• thyroid disorders

Infections

Maternal infections can cause congenital abnormalities and birth defects along with conditions such as hearing loss, visual impairment, and intellectual disabilities.

• rubella (measles) virus
• autoimmune diseases
• herpes simplex virus
• syphilis

Alcohol

One of the most commonly used teratogens is alcohol. Alcohol use during pregnancy is the leading preventable cause of intellectual disabilities in children in the United States Alcohol consumption, particularly during the second month of prenatal development but at any point during pregnancy, may lead to neurocognitive and behavioral difficulties that can last a lifetime. Risks of drinking alcohol while pregnant include:

• miscarriage
• pre-term birth
• sudden infant death syndrome (SIDS)
• fetal alcohol syndrome (FASD)

Drugs and Chemicals

When pregnant females ingest or absorb these, they may cause a variety of different effects based on specific agent, amount of exposure, and timing. This category includes

• heavy metals (including lead)
• insecticides and herbicides
• prescription and over the counter drugs (OTCs), including some vitamins
• illicit and recreational drugs
• cigarettes/nicotine
• caffeine

While there are many, many potential teratogens, the following tables look at the effects of some different types of teratogens. The risks of exposure vary based on lifestyle and health.

Fig. 2.7.1. – Drugs as Teratogens

Teratogen	Potential Effects
Caffeine	Moderate amounts of caffeine (200 mg or around 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.
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).
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 results 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.
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 experience withdrawal).
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

Heroin	Using heroin during pregnancy can cause birth defects, placental abruption, premature birth, low birthweight, neonatal abstinence syndrome, still birth, and sudden infant death syndrome (SUDS).
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.
Prescription drugs	Some prescription drugs can cause birth defects that change the shape or function of one or more parts of the body that can affect overall health. Pregnant women should consult their health care provider before discontinuing or starting new medications
Herbal or dietary supplements	Except for some vitamins, little is known about using herbal or dietary supplements while pregnant. 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

Fig. 2.7.2. – Environmental Teratogens

Teratogen	Potential Effects
Lea	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.
Mercury	Exposure to mercury in utero can cause brain damage and hearing and vision problems.
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.
Solvents	These chemicals include de-greasers, 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.

Fig. 2.7.3 – Maternal Infections as Teratogens

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

Fig. 2.7.4 – Pet/Animal Teratogens

Teratogen	Potential Effects
Toxoplasmosis	This parasite can be passed through cat feces and undercooked meat (especially pork, lamb, or deer meet). If the fetus is infected it can cause miscarriage, stillbirth, hydrocephalus, macro or microcephalus, vision issues, and damage to the nervous system.
Lymphocytic choriomeningitis	This virus carried by rodents including mice, hamsters, and guinea pigs. 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

Sources

• Overstreet,, Laura. Chapter 3: Prenatal Development – Environmental Risks:Teratogens. Lifespan Psychology. Licensed under CC BY 4.0.
• Prescription drugs, over-the-counter drugs, supplements and herbal products (n.d.). Retrieved from: March of Dimes.org.
• Tantibanchachai, Chanapa, Teratogens. Embryo Project Encyclopedia ( 2014-01-22 ). Licensed under CC BY-NC-SA 3.0.