Chapter 1. Teratogens

Synopsis

Human Development Video Activity
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You must read each slide, and complete any questions on the slide, in sequence.
embryonic period
The prenatal stage of development from approximately 3 weeks to 8 weeks after conception during which the embryonic cells first resemble a human being. By the end of the embryonic period, most basic organs have developed.
germinal period
The earliest stage of prenatal development that begins with conception and lasts until implantation in the uterus at anywhere from 6 to 12 days after fertilization. Often the germinal period is used to refer to the first 2 weeks after fertilization.
genotype
The complete set of genes for an organism. The complete genetic inheritance for an organism.
implantation
The process of the blastocyst attaching to the uterine lining. Implantation occurs anywhere from 6 to 12 days after fertilization. Upon successful implantation, the mother’s hormones trigger her menstrual cycle to stop.
spontaneous abortion
Also known as a miscarriage. A pregnancy that ends on its own before the 20th week.
teratogen
An agent or condition that has the ability to interfere with healthy prenatal development and may lead to birth defects or even death.

Teratogens

A close-up of the head of a fetus in the womb

Author

Catherine F. Robertson, Grossmont College
S. Stavros Valenti, Hofstra University

Synopsis

Teratogens are substances and conditions that can impair prenatal development and lead to birth defects or even death. Teratogens may include medications, diseases, infections, environmental pollutants, psychoactive drugs, and even poor nutrition.

REFERENCES

Berry, R. J., & Zhu, L. (2002). Folic acid alone prevents neural tube defects: Evidence from the China study. Epidemiology, 13, 114–116.

Cohen, L., Friedman, J., Jefferson, J., Johnson, E., & Weiner, M. (1994). A reevaluation of risk of in utero exposure to lithium. JAMA 27(12), 146–150.

Friedman, J., & Polifka, J. (1994). Teratogenic effects of drugs: A resource for clinicians (TERIS). Baltimore, MD: The Johns Hopkins University Press.

Lightfoot, C., Cole, M. & Cole, S. R. (2009). The Development of Children (6th ed.). New York: Worth Publishers.

Moore, K., L., & Persaud, T. V. N. (1998). The developing human: Clinically oriented embryology. Philadelphia: Saunders.

Mountain States Genetics. (1995). Teratogen update. Genetic Drift, 12. Retrieved August 29, 2005, from http://www.mostgene.org/gd/gdvol12h.htm

Nelson, C., & Demmler, G. (1997). Cytomegalovirus infection in the pregnant mother, fetus, and newborn infant. Clinics in Perinatology, 24, 151–160.

Organization of Teratology Information Services (OTIS). (2005). Fact sheets. Retrieved August 29, 2005 from http://otispregnancy.org/otis_fact_sheets.asp

Physical and Theoretical Chemistry Lab. (2005). List of known and suspected teratogens. Retrieved August 30, 2005, from http://ptcl.chem.ox.ac.uk/MSDS/teratogens.html

The Teratology Society. Metabolic teratogens. Retrieved August 29, 2005, from http://teratology.org/jfs/teratologyindex.html

The Teratology Society. Pharmaceutical teratogens. Retrieved August 29, 2005, from http://teratology.org/jfs/teratologyindex.html

The Teratology Society. Recreational teratogens. Retrieved August 29, 2005, from http://teratology.org/jfs/teratologyindex.html

Trasler, J., & Doerksen, T. (1999). Teratogen update: Paternal exposures-Reproductive risks. Teratology, 60, 161–172.

Teratogens: The Germinal Period

Observe the development that takes place during the germinal period.

The term teratogen refers to any environmental insult to the developing fetus at any point during the prenatal period. A teratogen can cause structural abnormalities, central nervous system damage, mental retardation, and slowed intrauterine growth. It may even terminate a pregnancy.

It is believed that if exposure to teratogens occurs during the germinal period, which is the first two weeks of gestation, the teratogenic agent will probably destroy the organism before implantation occurs. During the germinal period, it is estimated that approximately 45 percent of pregnancies end in spontaneous abortion, which may occur before a woman even realizes that she is pregnant.

Teratogens: The Embryonic Period

This fetus is at 10 weeks. Even though this fetus is past the embryonic period, it is still at a vulnerable time of development for exposure to teratogens

Beginning at the third week of gestation and continuing throughout the embryonic period, susceptibility to most teratogens is at its greatest. The reason for this is because all of the major organ systems, such as the circulation, nervous, and digestive systems, are beginning to develop during this time. The movement of cells to their final destinations and the differentiation of cells into their specific roles can be disrupted if the chemistry of the uterus is changed by the introduction of a teratogen, such as alcohol, the HIV virus, or radiation.

Radiation, for example, appears to have a teratogenic effect on fetal brain development, specifically between the eighth and sixteenth week of gestation. During this period of prenatal development, large numbers of brain cells are forming and moving (“migrating”) to their final positions. Radiation can disrupt this migration and interfere with the development of the brain.

Principles of the Influence of Teratogens

These boys with congenital limb and facial deformities were photographed at a children’s home for victims of the Chernobyl Nuclear Power Plant accident in 1986. While research does reveal that radiation is harmful to mother and fetus, the effects depend on the extent of exposure and the stage of prenatal development during exposure. Debates are still ongoing about the exact details of the extent of prenatal damage that radiation exposure causes. More research is needed.

Many factors affect how a teratogen does or does not interfere with the fetus’s growth. The introduction of a teratogen or teratogens certainly increases the risk of developmental problems for the fetus, but the presence of a teratogen or teratogens does not guarantee that there will be any problems. While the effects of teratogens on the fetus vary tremendously, there are some principles that hold true about the influence of teratogens on fetal development.

– Genetic vulnerability: Certain women and certain fetuses may be more or less vulnerable to particular teratogenic agents because of their genetic inheritance, or genotype.

– Timing of exposure: The age of the developing fetus is critical in determining a teratogen’s effect. Some teratogens only affect development during a highly precise and/or narrow range of time (e.g., thalidomide) while other teratogens can harm the fetus at any point or across a broader range of time (e.g., alcohol).

– Amount of exposure: The greater the dose of or duration of exposure to a teratogen or to multiple teratogens, the likelihood of a fetal response or reaction increases.

– Specific effects: Each teratogen acts in a distinct manner on specific cells of a developing organism to cause a potentially debilitating pattern of abnormal development. For example, the drug thalidomide generally only causes deformity in the arms and legs.

– Maternal condition: The mother’s age, nutrition, and physical and emotional condition all affect how a teratogen might impact a fetus.

– Whether the mother is affected: Some teratogens that have minimal to no risk to the mother may pose a great threat to the developing fetus. In some cases of rubella (German measles), the pregnant mother may only mildly affected and may not even be aware that she is infected while her fetus is at serious risk.

Interaction of Teratogens

Pregnant women should always consult their doctors and/or pharmacists when they are considering taking any supplement or medication.

In many pregnancies, more than one teratogen may introduced, such as a mother with poor nutrition habits who suffers from liver dysfunction. The presence of multiple teratogens can lead to an interaction effect or even a cumulative effect.

In the case of a woman who smoked and used alcohol throughout her pregnancy, the combined effect of both smoking and drinking does much more harm to the fetus than either one of these teratogens could do alone.

Categories of Teratogens

Under each category below, a few representative teratogens are shown. On the next screen, you will be asked to categorize some of these substances and conditions.

Medicines Maternal Diseases and Infections Environmental Pollutants Psychoactive Drugs Poor Maternal Nutrition
any drug prescribed by a doctor as well as over-the-counter drugs and remedies viruses and diseases that can harm or interrupt development in the womb pollutants in the air, soil, water, or food that may have teratogenic effects non-prescription and non-medicinal drugs that affect the mind diet that includes foods that pregnant women should avoid or lacks certain vitamins or minerals, proper caloric intake, or sufficient protein or fats
Examples Examples Examples Examples Examples
Accutane (used for acne), Tetracycline & Streptomycin (antibiotics), Excedrin Extra Strength rubella (German measles), syphilis, HIV/AIDS lead, mercury, radiation alcohol, cocaine, heroin, marijuana, tobacco lack of folic acid, excess caffeine, raw or undercooked meat, fish, and eggs

Review of Categories of Teratogens

For each teratogen, indicate the category to which it belongs.

Question 1.1

Alcohol 27YwbviIir4MgoVYHheWdC5HJZk+CGTqGDQfTun0iFQiy5jUWIvOeZZ+meKBX/AeFuAPYxR8IY+PnlqWGAIR3+ArB7wTXmMv3jLFlsLuUgbye7GaQZp5XU7pk8dUCouH5gJVajm1Av1QIVJFmIa6zg==

Streptomycin s578uoI7hTfJUz5Vv+uXz2eNRY0UzKYWtSGcxbxRajDua2nypzEjM/iQahN0Gge0crKZpzB9IizW1SDeJ1XoF8kw75ze6kaASuTQYwcU83GRvCbeZX7mj2z/EKYablMYMhA2ukhg1swgrf6gG1rOUw==

Heroin 27YwbviIir4MgoVYHheWdC5HJZk+CGTqGDQfTun0iFQiy5jUWIvOeZZ+meKBX/AeFuAPYxR8IY+PnlqWGAIR3+ArB7wTXmMv3jLFlsLuUgbye7GaQZp5XU7pk8dUCouH5gJVajm1Av1QIVJFmIa6zg==

HIV/AIDS WFcyKnF+xdbAMLKixwhM6mmErvmOKdrdT/FD8LKzmzpLvVmaXJZJcOmvO8zi6H6MuEknf9ppeEN71Q0+nNgH+45HFBrpj6DlQF2FAYw63mXq1rc7WhvPwdkH16NjcDMkUJ385gatZly92nUFgdUrjg==

Lack of folic acid WHg6M71mOKE9DiIvU81BYVjhs4mJl1C/1J3+vISpG7RtGyyQPDH/q9MtXzz8L/k1+Z2qjyYtG6P739Nha8v2P1OMtciNo+Dq9dPGj/jfvZyJTj7cW/L7GAy+ZRYCehZfrHKHiBk1LSIsY71o7VKN+A==

Tobacco 27YwbviIir4MgoVYHheWdC5HJZk+CGTqGDQfTun0iFQiy5jUWIvOeZZ+meKBX/AeFuAPYxR8IY+PnlqWGAIR3+ArB7wTXmMv3jLFlsLuUgbye7GaQZp5XU7pk8dUCouH5gJVajm1Av1QIVJFmIa6zg==

Lead 68h4R3OfnJwdHwZom1ZVdPqDCIZyCqNNG8UWJ9w1l/npm51Mh+db5E1RW34E12BhhYYKUxL0m6XXtRqDWqM13KFXXjtTH8TClN3U1fAMLrFrxyl/rgIHek0uQ74lnOcsRBiJvjLlCP+An7b8LokNVA==

Raw or undercooked meat, fish, and eggs WHg6M71mOKE9DiIvU81BYVjhs4mJl1C/1J3+vISpG7RtGyyQPDH/q9MtXzz8L/k1+Z2qjyYtG6P739Nha8v2P1OMtciNo+Dq9dPGj/jfvZyJTj7cW/L7GAy+ZRYCehZfrHKHiBk1LSIsY71o7VKN+A==

Marijuana 27YwbviIir4MgoVYHheWdC5HJZk+CGTqGDQfTun0iFQiy5jUWIvOeZZ+meKBX/AeFuAPYxR8IY+PnlqWGAIR3+ArB7wTXmMv3jLFlsLuUgbye7GaQZp5XU7pk8dUCouH5gJVajm1Av1QIVJFmIa6zg==

Mercury 68h4R3OfnJwdHwZom1ZVdPqDCIZyCqNNG8UWJ9w1l/npm51Mh+db5E1RW34E12BhhYYKUxL0m6XXtRqDWqM13KFXXjtTH8TClN3U1fAMLrFrxyl/rgIHek0uQ74lnOcsRBiJvjLlCP+An7b8LokNVA==

Rubella WFcyKnF+xdbAMLKixwhM6mmErvmOKdrdT/FD8LKzmzpLvVmaXJZJcOmvO8zi6H6MuEknf9ppeEN71Q0+nNgH+45HFBrpj6DlQF2FAYw63mXq1rc7WhvPwdkH16NjcDMkUJ385gatZly92nUFgdUrjg==

Radiation 68h4R3OfnJwdHwZom1ZVdPqDCIZyCqNNG8UWJ9w1l/npm51Mh+db5E1RW34E12BhhYYKUxL0m6XXtRqDWqM13KFXXjtTH8TClN3U1fAMLrFrxyl/rgIHek0uQ74lnOcsRBiJvjLlCP+An7b8LokNVA==

Cocaine 27YwbviIir4MgoVYHheWdC5HJZk+CGTqGDQfTun0iFQiy5jUWIvOeZZ+meKBX/AeFuAPYxR8IY+PnlqWGAIR3+ArB7wTXmMv3jLFlsLuUgbye7GaQZp5XU7pk8dUCouH5gJVajm1Av1QIVJFmIa6zg==

Syphillis WFcyKnF+xdbAMLKixwhM6mmErvmOKdrdT/FD8LKzmzpLvVmaXJZJcOmvO8zi6H6MuEknf9ppeEN71Q0+nNgH+45HFBrpj6DlQF2FAYw63mXq1rc7WhvPwdkH16NjcDMkUJ385gatZly92nUFgdUrjg==

Tetracycline s578uoI7hTfJUz5Vv+uXz2eNRY0UzKYWtSGcxbxRajDua2nypzEjM/iQahN0Gge0crKZpzB9IizW1SDeJ1XoF8kw75ze6kaASuTQYwcU83GRvCbeZX7mj2z/EKYablMYMhA2ukhg1swgrf6gG1rOUw==

Excess caffeine WHg6M71mOKE9DiIvU81BYVjhs4mJl1C/1J3+vISpG7RtGyyQPDH/q9MtXzz8L/k1+Z2qjyYtG6P739Nha8v2P1OMtciNo+Dq9dPGj/jfvZyJTj7cW/L7GAy+ZRYCehZfrHKHiBk1LSIsY71o7VKN+A==

Correct.
Incorrect.

Assessment: Check Your Understanding

Question 1.2

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Correct! Susceptibility to teratogens is greatest during the embryonic period.
Sorry. Susceptibility to teratogens is greatest during the embryonic period.

Assessment: Check Your Understanding

These boys with congenital limb and facial deformities were photographed at a children’s home for victims of the Chernobyl Nuclear Power Plant accident in 1986.

Question 1.3

2ppYgjwVCQ8XXyBFUPbbkA7TpECv6w5ZdkWQOBgmDJ4XlqQXggPCWX54+GPJ4ailJDZrmKJNhL9wlWebodejV/R5GnTo2Tjc
The categories of teratogens are: medicines, psychoactive drugs, maternal diseases and infections, poor maternal nutrition, and environmental pollutants.

Assessment: Check Your Understanding

Nida, a 7-month-old girl with a congenital birth defect, with her mother at a press conference in New Delhi, India on April 29, 2008.

Question 1.4

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During the embryonic period, all of the major organ systems, such as the circulation, nervous, and digestive systems, are beginning to develop. The movement of cells to their final destinations and the differentiation of cells into their specific roles can be disrupted if the chemistry of the uterus is changed by the introduction of a teratogen. Therefore, the major organs are very vulnerable to teratogens during this period.

Congratulations! You have completed this activity.Total Score: x out of x points (x%) You have received a provisional score for your essay answers, which have been submitted to your instructor.