Teratogens and the Damage They Do

The Greek word for “Malformation or Monstrosity” is teras. This is the root of the words, teratogen and teratology. The study of teratogens is vital to the future health of newborns. The incidence of birth defects – some horrific in nature – can be lessened, but only if they can be isolated as a root cause of a particular abnormality. Some of the defects include severe mental retardation, cleft palates, and sadly, the birth of a baby with no arms or legs. Teratology is therefore, important for the futures of embryos and fetuses at risk. There are many teratogens that have been identified, but there are many more that remain anonymous. Those teratogens that have been identified are specific as to the anomalies they cause. Part of the problem with research is ethical in nature. For this reason, animals must take the place of humans in research. While not a perfect substitution by any means, it can lead research in the right direction. There are also a number of things that pregnant women can do to minimize the odds of these abnormalities occurring.

Teratology Background Information

How professional Define Teratogens

A look at how professionals in the field define teratogens and teratology is fairly consistent. According to Laura E. Berk, a teratogen is, “any environmental agent that causes damage during the prenatal period.” Writing for Columbia University, Dr. Wendy Chung defines teratology as, “the study of abnormal development in embryos and the causes of congenital malformations or birth defects.” Finally, The Children’s Hospital of Wisconsin’s website simply states that, “A teratogen is an agent, which can cause a birth defect.” Sometimes, simplicity is best to describe something that’s complicated.

A Brief History

The history of teratology dates back to 1867 when physician and bacteriologist Robert Koch began experimenting with anthrax, and found that it was capable of causing disease – and that the disease was transferable from one host to another. In efforts to find a causal relationship between a specific agent and a specific disease, he used various criteria that he hypothesized were necessary for this determination.

In 1890, he created a checklist of sorts known as Koch’s Postulates which states the following:

“A scientist must find the same microbe in every person with a given disease. Furthermore, the specific microbe must be able to be grown on pure culture medium in the lab and when reintroduced into a healthy animal or person must produce the disease again.” Koch’s Postulates became the starting point for many studies, but they were not perfect. One important factor that runs in opposition to the postulates is the fact that a virus needs a living cell to replicate. Obviously, this implies that it would not be capable of growing in a culture without a host cell to invade. Despite the flawed criteria, Koch is often credited with being the first to prove that diseases are caused by microbes.

The Science of Teratology

An Overview

Teratology is a scientific discipline that has grown in scope and stature since its inception. It is based in the belief that abnormalities in embryo and fetal development are caused, in some cases, by external or environmental sources. While many of the malformations are noticeable at birth, there are a comparable number that develop later in life – even though they were present at birth. These defects range in severity from inconsequential, like ear tags, to major, like missing limbs. Also of significance: “The greater the number of minor malformations, the greater the likelihood of an associated major malformation.”

The Timing of Teratogn Introduction

During embryonic and fetal development, there are critical periods when the embryo or fetus is most susceptible to foreign agents. The timeframe when certain organs and body parts are at the peak of their development, is also the timeframe when these same organs and body parts are most in danger of being adversely affected by the introduction of a teratogen. According to Dr. Chung, “The embryo is most susceptible to teratogenic agents during periods of rapid differentiation.” And from their article, Human Teratogens: A Critical Evaluation, written for the Motherisk Program at the Hospital for Sick Children in Toronto, Orna Diav-Citrin, M.D. and Gideon Koren, M.D., FACCT, FRCPC specifically note the following: “Teratogens act with specificity in that they produce specific abnormalities at specific times during gestation.”

The specificity with regard to when a teratogen is introduced is of utmost import. An example from the Children’s Hospital of Wisconsin states that a teratogen that “has the potential to interfere with the closure of the neural tube… exposure to the teratogen must occur in the first 3.5 to 4.5 weeks of the pregnancy, since this is when the neural tube is closing.” This is particularly serious as the neural tube becomes the brain and spinal cord. Common defects resulting from this are spina bifida and anencephaly. One can see that there is a small window of opportunity for a teratogen to be introduced – approximately one week in which the neural tube is closing. Other teratogens are capable of affecting other parts simultaneously or at other times depending on the organ or body part in the rapid development stage. It is also believed that two or more teratogens are responsible for various birth defects at various times – in various conditions. These multiple invasive agents merge in specific combinations to facilitate the formation of abnormalities.

The most susceptible period for a teratogen to cause damage during a pregnancy is in the embryonic stage which covers the first eight weeks. This is the phase when the most development takes place. By the time that fetal growth occurs, most (but not all) critical periods of development have passed. For example, the heart and limbs are fully formed by the end of the embryonic stage. The ears, eyes, teeth, and palate are nearly complete – although they are still developing, and therefore remain at risk during the fetal stage. The central nervous system is exposed throughout the pregnancy, but at high risk only until the 20th week, approximately.

Teratogen-linked Malformations

Teratogens are Responsible for a wide range of Abnormalities

Teratogens have been linked to various birth defects, and abnormalities of all levels of severity. Some congenital abnormalities include, but are certainly not limited to heart disease, mental retardation, cognitive problems, missing or malformed limbs, and all forms of cancer.

It is also recognized that congenital defects are not uncommon. It is estimated that between 1-3% of the general population are born with major defects. That statistic rises to approximately 5%, or one in twenty, when adult abnormalities are considered, and believed to have been present at birth. Of all major birth defects, about 25% are thought to be genetic in origin. A full 65% have an etiology, or origination, that is unknown. The remaining 10% are suspected of being caused by environmental exposures, including radiation and infections.

Teratogens are also target-specific. That is, they do not affect each organ or limb equally. Different teratogens attack different body parts at different times. For example, thalidomide can cause disfigured or missing limbs if taken during the early embryonic stage – as early as week four. Exposure to a virus during the embryonic stage is capable of causing mental retardation, eye cataracts, deafness, urinary, genital, heart, and intestinal defects. On the other hand, if the exposure happens in the fetal stage, damage is less likely to occur. One of the most tragic teratogens has to be alcohol, because it is 100% avoidable. It can cause mental retardation and other anomalies throughout the pregnancy.

Causal Teratological Factors

Defect-Related Variability

The amount of damage caused by teratogens is dependent on other variables such as heredity, dose, and other factors. Heredity is important in that it matters how a particular person reacts to an environmental reactant – everyone is different. Logically, dose makes a difference as well – the larger the dose, the greater the harm. Exposure to radiation, environmental pollutants, and smoke from tobacco products – even second-hand smoke are also risk factors. The consumption of alcohol, prescription and illegal drugs are also capable of causing multiple birth defects.

Radiation Exposure

Exposure to radiation during pregnancy can be particularly dangerous. The bombings of Hiroshima, Nagasaki, and the Chernobyl nuclear power plant accident in Ukraine, caused untold damage to those born to women who were pregnant during the events. Slow physical growth, underdeveloped brains, and extreme physical deformities are some of the malformations that were caused by the exposure. Even a seemingly-innocent X-ray has been known to be responsible for an increase in childhood cancer.

Mercury

The environment is literally filled with man-made, as well as naturally-occurring pollutants. Mercury, PCBs, lead, and thousands of other substances have been introduced into the environment – and many new ones are released each and every year. Mercury has been in our water supplies and oceans since the 1950s when various industrial plants released waste containing it. Children have been born with many abnormalities as a result. Physical deformities, lack of coordinated movements, and mental retardation have all been traced to mercury. Even today, most fish contain a certain amount of mercury – some more than others. Sixty years later, pregnant women are still advised to avoid eating fish – in particular, swordfish, tuna, and shark.

PCBs

PCBs were used in electrical equipment. Like mercury, they ended up in the food chain as a result of being released as waste. Low birth weight, smaller heads, problems with skin, gums, and nails have all been linked to even low levels of PCB contamination. Taiwan has been especially hard hit by PCB pollution in the form of rice-oil.

Lead

Until the 1980s, lead was an ingredient in most paint. Older buildings still have lead-based paint covering the walls. Some of the problems associated with lead exposure include brain damage, low birth weight, and many various physical defects. Lead has also been shown to be the root cause of antisocial behavior in adolescents.

Tobacco

Thankfully, smoking while pregnant is not nearly as widespread as it once was. The American Heart Association and others have helped tremendously as far as making consumers aware of the dangers of smoking. Obviously, while no amount of smoking is healthy, the risks are without doubt, dose-related. The more one smokes – or is exposed to smoke – the greater the potential damage to the embryo and fetus. Smoking mothers are more likely to have newborns who are unresponsive, have increased muscle tension, low birth weight, impaired heart rate, and asthma, as well as a greater likelihood of cancer in later childhood. Even passive smokers – those who don’t smoke themselves, but are affected by those around them – are in danger of having babies with low birth weight, respiratory illnesses, and long-term attention impairment.

Alcohol

Consuming alcohol is a very bad idea for pregnant women. Fetal alcohol syndrome, partial fetal alcohol syndrome and other alcohol-related conditions are especially tragic in that they are completely avoidable. Alcohol is known to be a causal factor for babies with a plethora of abnormalities ranging from slight to extreme, and everything in between. Much of the deformities depend on how much and how often the mother drank. Slow growth, brain damage, and problems involving the heart, immune system, genitals, eyes, ears, nose, throat, are all possibilities. Other problems resulting from alcohol consumption include the development of impaired judgment, poor motor skills, inappropriate sexual behavior, mental health issues, and other problems.

Drugs

Drugs, as prescribed by a doctor, are generally safe for the mother, but the same cannot be said of the embryo or fetus. All drugs – legal or illegal – have the potential to harm the unborn. As a result, all pregnant women are advised to avoid all medication unless absolutely necessary during the first eight weeks.

Discussion and Conclusion

Research Studies

It should be obvious that there are no studies involving human testing for ethical reasons. Animals, while not human, and with different gestational periods, are used to test drugs and suspected teratogens. If more than one species shows the same susceptibility to a particular teratogen, it is generally assumed that there is good possibility that there exists a potential threat to humans. The only studies involving humans are necessarily retrospective in nature. That is, once an abnormality has been identified in a newborn, there is the difficult and time-consuming task of retracing the steps of the mother since conception. Today, this is still, in essence, the only way of searching for, and discovering a possible causal link to a teratogen.

Drug Categorization

In 1980, drug companies began to categorize their products – labeled by potential threat level to the unborn. There were five categories ranging from category A which states that the medication has shown no ill effects, to category X, which states the medication is linked to certain birth defects, and therefore should not be used by pregnant women. While this seemed to be a logical step to assure the highest degree of safety possible, some professionals complained that the pharmaceutical companies were perhaps more worried about lawsuits than birth defects resulting from the use of their products. However, the existence of category X does offer concrete evidence, and shows what to avoid – as known fetal abnormalities have been shown in both humans and animals. So, while not perfect, and sometimes confusing, the labeling would appear worthy of keeping – and improving.

Minimizing Risk

It’s clear that healthy pregnancies are dependent on a myriad of factors. There is no way of eliminating absolutely, the possibility of a congenital malformation. Short of living in a self-contained environmental bubble, it just cannot be accomplished. Risks can be reduced however, by using common sense during a pregnancy. Being careful of what one ingests – including prescription drugs; avoiding alcohol, tobacco, and other toxins – as well as those in the environment is crucial. It’s also important to eliminate any prescribed drugs that are not medically essential.

Teratogens are virtually everywhere. They are in the food we eat, the water we drink, and the air we breath. While there are obvious differences in food contaminants, fish and raw or undercooked meat should be avoided. Many people have less control over the water they drink, but purified bottled water is obviously preferable to common tap water – especially in underdeveloped areas. Breathing air certainly cannot be helped, but avoiding high pollution zones would be wise. Today, there are more environmental teratogens than ever before – with more introduced every day. While progress is being made, research unfortunately, is lagging far behind – mainly due to the ethical limitations inherent in the studies.