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understanding the environmental causes of birth defects in a modern world

Abstract: Since the industrial revolution and the advent of the modern world there has been an exponential increase in the amount of pollutants that all living organisms are exposed to. Many of these environmental pollutants can act as agents in causing birth defects. Bacteria, viruses, medications, self ingested substances such as alcohol and numerous other agents may also act as teratogenic or mutagenic mediators. All shall be discussed in this article. It is vital for all prospective parents and health professionals working in the field of reproductive medicine to understand the environmental causes of birth defects.

Much research, particularly over the last century, has clearly established the relationship that the environment imparts on the developing infant. The environment can either have positive or negative health effects on the infant both in pregnancy and post birth. Whilst many environmental causes of birth defects have now been clearly identified, the list of possible teratogenic and mutagenic agents is growing within our modern industrialized world. Birth defects can vary from inducing infant mortality, to neurobehavioural dysfunction (including mental retardation) and numerous physical dysmorphologies (including retarded growth). It is not known what actual percentage of birth defects have an environmental (including drugs) cause but Porth suggests that 2-3% of birth defects have a known environmental or drug origin (Porth, p. 147). This suggests the need for fertile people to err on the side of caution with exposure to chemicals, drugs and other environmental agents, as causes of birth defects are an ongoing research area and one that may never be fully understood, due to the changing world we live in.

Known environmental causes of birth defects include alcohol, pharmaceutical and non pharmaceutical drugs, cigarette smoking, bacterial and viral pathogens, heavy metals, radiation and altitude. This paper shall examine these environmental agents and the possible effects on the developing fetus both in in-utero life and after birth.

Alcohol is the most common cause of preventable mental retardation in children globally. Alcohol can freely cross the placental barrier and consumption during the early months when the fetal detoxification systems are still developing places the child at a much heightened risk of congenital birth defects; however maternal alcohol ingestion can have harmful effects on the fetus at any stage of the pregnancy. The effects of alcohol consumption to the child depend on the amount consumed and also, at which stage of pregnancy. ‘Animal studies suggest that the ferotoxic effects of alcohol are dose dependent rather than threshold dependent’ (Porth, 2005, p. 149). A secondary effect of alcohol consumption is the reduced nutritional status of both the mother and infant in-utero, which may potentiate other pregnancy associated risks such as hypertension and gestational diabetes.

Fetal Alcohol Syndrome (FAS) is used to describe the cluster of mental, physical and neurobehavioural symptoms that arise with more severe alcohol consumption by the mother (Whitney & Rolfes, 2008, p. 543). Exposure to alcohol during the first trimester may result in damage to developing organs such as the brain, heart and kidneys. Exposure during the second trimester increases the likelihood of spontaneous abortion; whereas exposure in the third trimester may result in both brain and body retardation (Whitney & Rolfes, 2008, pp. 544-545).

A retrospective study into American Indian children showed that when compared with the control group, the children with FAS had increased rates of varying forms of facial dysmorphology, growth retardation, muscular system problems, and central nervous system dysfunction. High rates of behavioural problems, learning difficulties and hospitalization were also statistically higher than the control group (Valborg, Leonardson, Neff-Smith & Faan, 2004, pp. 635-640). The health of Australia’s indigenous people is of increasing concern both nationally and globally. Indigenous Australians have far poorer health status and particularly affected are indigenous children. Indigenous children have higher rates of FAS and their infant mortality rates are three times than the non-indigenous population (ABS, 2004, p.8).

Statistics from the Australian Bureau of Statistics show that an alarming 47% of Australian women consume alcohol when pregnant and/or breastfeeding, however the ‘proportion who are drinking at risky levels in pregnancy is not known’ (ABS, 2004, p. 10). Whilst the affects of alcohol consumption to the child are irreversible, FAS is the most common cause of preventable mental retardation. The plethora of research into this area now suggests that no amount of alcohol is safe for the pregnant woman (Coyne, De Costa, Heazlewood, & Newman, 2008, pp. 240-7) (Walpole, Zubrick, & Pontre, 1990, pp. 297-301).

Heavy metals are another known cause of birth defects, particularly well documented are the harmful effects of lead, mercury, cadmium and arsenic. Infants exposed to these agents in-utero may have serious health side effects due to these substances readily moving across the placental barrier, whilst the mother may be unaffected and unaware of the contamination. A common form of mercury contamination is through the consumption of large fish, which store a greater amount of mercury in their systems (compared to smaller sea creatures). This causative relationship was clearly seen in Japan, in the Bay of Minamata in 1960 where 121 cases of mercury poisoning were confirmed. An increased rate in infants was evident, amongst whose mothers who had consumed seafood regularly from the bay. Birth defects documented included an array of neurological symptomatology, including ‘blindness, deafness, lack of coordination, and intellectual impairment’ (Whitney & Rolfes, 2008, p. 675).

Lead is another major environmental cause of birth defects, causing mental retardation and psychomotor dysfunction. Lead may be absorbed through the gastrointestinal tract or lung tissue, and inflicts most damage upon red blood cells, kidney tissue and gastrointestinal tract. The ability of red blood cells to utilize iron is reduced, thus anemia may be a presenting sign of latent lead poisoning. Most lead is stored in the bone tissue, competing with calcium for remodeling and it is excreted by the kidneys. Deficiencies in zinc, calcium and/or iron will increase the absorption rates of lead. Common sources of lead are paint, soils, water (in old homes with lead solder joints) and newsprint (Porth, 2005, pp. 110-111).

Maternal nutrition is of utmost importance for the female and the developing fetus. The diet should nurture both the mother and fetus but can also be the source of environmental contaminants leading to birth defects. Agents in the diet which may have adverse reproductive outcomes on the child include caffeine, mercury contaminated seafood (as discussed previously) and foods containing bacteria such as listeria. Caffeine consumption in pregnancy is contraindicated in large amounts during pregnancy, due to high intake users having higher rates of fetal mortality. This is due to caffeine freely crossing the placental barrier, coupled with pregnant women having a slower metabolism of caffeine (Whitney & Rolfes, 2008, p. 532). Studies into caffeine consumption in pregnancy offer conflicting results, with no clear birth defects established, however the risk of miscarriage is statistically higher in women consuming large amounts of coffee.

Food may also be a potential source of bacterial pathogens, such as listeria. Listeria infection may result in miscarriage, premature birth or stillbirth. Due to the possibility of such adverse outcomes, the avoidance of high risk foods is strongly advocated for pregnant women. Other bacterial agents are also known to be possible agents for birth defects, including inducing spontaneous abortion. These bacterial infections include syphilis, pneumonia, tuberculosis, typhoid and bacterial vaginosis. Jones & Lopez suggest that up to 16% of pregnant American women are carriers of bacterial vaginosis, which increases the likelihood of premature birth (2006, p. 279).

Certain viral pathogens can also have teratogenic effects, particularly if exposure if in the early weeks of life. Teratogenic viral agents include German measles, AIDS, smallpox, chicken pox, mumps and herpes. For these reasons, pre-natal screening of women is advocated to ascertain her immunity against chicken pox and German measles. The effects of in-utero contamination of German measles upon the fetus are well documented medically, with the teratogenic effects including ‘heart defects, blindness (due to cataracts), deafness, microcephaly (small brain), mental deficiency, cleft palate, harelip, and spina bifida (exposed spinal cord)’. The teratogenic effects are potentiated with exposure in the 3rd to 12th week of pregnancy (Jones & Lopez, 2006, p. 278).

Cigarette smoking is also a common cause of birth defects and largely avoidable, aside from passive smoking. It is thus advisable that the pregnant woman abstain from smoking and passive intake of cigarette smoke. Public health warnings about the dangers of smoking have increased in recent decades and the prevalence of smoking has decreased. One side effect of smoking that is commonly known is that the infant born to a pregnant female smoker may have a reduced birth weight. Maternal cigarette smoking may also ‘lower Vitamin C levels in the fetus, impair fetal growth, damage the fetus and placenta (including placenta previa), and lead to miscarriage, premature birth, or stillbirth’ (Jones & Lopez, 2006, p. 282). An increased susceptibility to Sudden Infant Death Syndrome (SIDS), childhood hearing problems and lowered IQ are also suggested by Jones & Lopez as possible birth defects from maternal cigarette consumption. A positive correlation has also been established between childhood asthma and respiratory diseases and maternal smoking in pregnancy (Whitney & Rolfes, 2008, p. 531). For this multitude of reasons, as well as the negative impact on maternal health, it is highly advisable for women not to smoke in pregnancy.

It is well established and fairly commonly known that many drugs, whether pharmaceutical or non-pharmaceutical, can have an array of serious health consequences. These side effects may be more pronounced in the infant due to the crossing of the placental barrier and to re-iterate previous discussions, the effects will depend upon the amount consumed and at which stage of fetal life this occurred. Non prescription drugs capable of inducing birth defects include cocaine, heroin, methadone and Lysergic acid diethylamide (LSD). The active ingredient of marijuana, tetrahydrocannabinol may also reduce placental estrogen output, thereby increasing the likelihood of miscarriage (Jones & Lopez, 2006, p. 282). Birth defects from narcotic use include reduced birth weight, perinatal death, central nervous system dysfunction and neurobehavioural dysmorphologies. An increased rate of SIDS is also noted amongst this sub group of infants (Whitney & Rolfes, 2008, p. 530).

Radiation is contraindicated in pregnancy due to both teratogenic and mutagenic effects; these effects are seen with strong radiation doses, whereas there is ‘no evidence that diagnostic levels of radiation cause congenital abnormalities’ (Porth, 2005, p. 147). Generally, radiation is avoided in pregnancy and even with possible pregnancy in fertile women.

Additionally, high altitude , being an altitude of above 8000 feet has associated increases in lower birth weight infants, increased rates of jaundice and neonatal fatality (Jones & Lopez, 2008, p. 283).

Importantly, it is not just non-pharmaceutical drugs which may instigate teratogenic effects to the fetus, with many pharmaceutical drugs possible of inducing birth defects. Drugs known to have teratogenic effects include anticoagulants such as Warfarin, anticonvulsants, cancer drugs, accutane (Vitamin A derived), propylthiouracil, tetracycline and thalidomide (Porth, 2005, p. 147). It is established that there are a number of factors that determine the teratogenicity of the drug which include the amount of the drug taken, the duration of ingestion, the period of time in fetal development when it was taken, the stage of placental development, the lipid solubility of the drug (and ease to cross the placental barrier) and the molecular weight of the drug (and ease to cross the placental barrier) (Porth, 2005, p. 147). The drug thalidomide is one of the most widely known teratogenic drugs, given to women in the late 1950s to the early 1960s to treat morning sickness. Its teratogenic ramifications included the development of arms and hands but without limbs. More recently, the drug diethylstilbestrol was used to prevent miscarriage. This drug had mutagenic effects, with the offspring of women who had ingested the drug, having chromosomal abnormalities of their reproductive tracts. In females, this presented as increased rates of vaginal and cervical cancer, increased miscarriage rates and premature births. In male offspring, the birth defects included undescended low testes and a low sperm count (Jones & Lopez, 2008, p. 279).

Other drugs such as aspirin can also be teratogenic, which is perhaps more dangerous given a large number of the population views them as perfectly safe. When aspirin is taken over a period of several days during heart organogenesis, the anti-prostaglandin effects of the aspirin act to close the ductus arteriosus. Other drugs having anti-prostaglandin effects can similarly affect the fetal heart (Lopez & Jones, 2008, pp. 282-3).

Similarly, natural medicines should be prescribed by a practitioner knowledgeable about maternal and fetal health. Of particular caution is Vitamin A, which should be kept to the 2700IU daily intake. Vitamin A ingested in an excessive amount may be teratogenic, with birth defects observed on fetal head, heart and brain tissues.

To conclude, there are a multitude of environmental agents capable of producing birth defects if exposure occurs during fetal life. Of crucial importance in the effects to the fetus are the amount of the teratogenic agent, the duration of the ingestion, the stage of placental development, the lipid solubility and molecular weight of the substance and crucially, the stage of fetal life in which the substance was ingested. Teratogenic agents are most harmful during the 3rd to 12th weeks of fetal life when organ differentiation is occurring but nonetheless, at any stage of the pregnancy harmful effects may be exerted. Pre-conceptual health care and pregnancy care from conception is of utmost importance. Diagnostic screening tools, such as checking for immunity to Rubella or checking ante-natally for bacterial vaginosis should be routinely practiced to avoid unnecessary exposure of agents capable of producing birth defects. Education should be deployed so that both future parents understand their environment.

Janelle Repacholi practices holistic, naturopathic medicine, specialising in fertility and children’s health @ NatMed Natural Medicine Clinic www.natmed.com.au

References

Australian Bureau of Statistics (2004), Australian Social Trends Article: Australia’s Babies, Canberra.

Coyne, K.L., De Costa, C.M., Heazlewood, R.J. & Newman, H.C. (2008) Pregnancy characteristics of women giving birth to children with fetal alcohol syndrome in Far North Queensland, Australian and New Zealand Journal of Obstetrics and Gynaecology, V 48 (3), pp. 240-247.

Jones, R.E. & Lopez, K.H. (2006) Human reproductive Biology (3rd ed.), Academic Press: Burlington, USA.

Porth, C. (2005) Pathophysiology Concepts of Altered Health States (7th ed.). Lippincott-Raven Publishers: Philadelphia, p. 147

Whitney, E & Rolfes, S.A. (2008), Understanding Nutrition (11th ed.), Thomson Wadsworth: Belmont, USA.

Valborg, L.K., Leonardson, G., Neff-Smith, M., Faan, E.B. (2004), Characteristics of children who have full or incomplete Fetal Alcohol Syndrome, J Pediatric; 145, pp. 635-40.

Walpole, I., Zubrick, S & Pontre, J. (1990) Is there a fetal effect with low to moderate alcohol use before or during pregnancy? J Epidemiol Community Health V 44 (4), pp. 297-301.