By Peter Montague
The Birth Defects Monitoring Program (BDMP) is a US government effort to monitor birth defects using data collected when newborn infants are discharged from hospital. The BDMP was initiated by the federal Centers for Disease Control (CDC) in 1974. The current BDMP database includes information on roughly 15 million births that have occurred at 1200 predominantly mid-sized community hospitals in the US during the past 20 years.
The BDMP database is not comprehensive (it does not include information on every birth that occurs in the US). Neither does it represent a randomly selected sample of births; therefore data from the BDMP cannot be considered representative of the entire "universe" of all US newborns. In 1987 the BDMP received information on 15% of all US births.
Nevertheless, as the CDC says, the BDMP "represents the largest single set of uniformly collected and coded discharge data on congenital malformations in the United States". It is simply the best information available on birth defects in the US.
CDC says that the BDMP "functions primarily as an early warning system; however, it can be useful also for correlating incidence patterns with such trends as the temporal and geographic distribution of drugs, chemicals, and other possible human teratogens". A teratogen is anything that causes birth defects. Examples are diseases such as German measles, infections, inherited genetic defects, radiation and certain chemicals.
In 1990, researchers looked for trends in the BDMP database, examining records for 38 types of birth defects from 1979-80 through 1986-87. During this seven-year period, of the 38 types of birth defects, 29 increased; two decreased; and seven remained stable (meaning they changed less than 2% per year during the period).
Some of the increases are explained by better health care and better diagnosis. For example, some heart defects are so serious that an infant might not have survived such a defect 10 years ago but might survive it today. Likewise, some of the heart defects might be revealed by high-tech medical diagnostic machines today, whereas they might have gone unnoticed 10 years ago.
However, many of the increases cannot be explained by better health care or better diagnosis. If a child were born 10 years ago with the iris missing from one or both of its eyes, chances are good that the mother or her doctor or a nurse would see it. (The iris is the part of the eye that makes blue eyes blue and brown eyes brown.) So the 5.2% annual increase in "aniridia" (absence of an iris) is very likely a real increase.
The same can be said for birth defects of the central nervous system, facial clefts, musculoskeletal defects and some of the gastrointestinal and genitourinary defects. Increases in these defects are very likely real increases.
Some of the increases are surprisingly large. For example, coloboma of the eye increased 9.6% each year during the period; this means the occurrence of this defect doubled during the study period. (Coloboma of the eye means a wedge-shaped piece is missing from the iris, or some other part of the eye is missing.) Other eye disorders (congenital cataract, for example) are increasing about 5% each year, thus doubling every 14 years.
Are most birth defects caused by the parents' genetic characteristics, or by something in the environment?
Norwegian study
In July of this year an important study of birth defects in Norway appeared in the New England Journal of Medicine. It indicated that environmental factors may be more important than previously thought.
Norway has maintained a medical birth registry since 1967; the registry now contains data on 1.5 million births. Norwegian and US researchers examined records of 371,933 women who had given birth to first and second children in Norway between 1967 and 1989.
For the 9192 women whose first infant had a birth defect, they examined the risk of similar or dissimilar effects in the second infant. And they examined the risk of a birth defect in the second child among mothers who lived in the same municipality during both pregnancies vs mothers who moved to a new municipality before the second child was born. (The control group was the 362,741 women whose first infant did not have a birth defect.)
The researchers found that 2.5% of all infants born in Norway have a birth defect. Examining 23 different kinds of birth defects, they found that in every category, mothers whose first infant had a defect were more likely to have a second infant with a defect, as would be expected if birth defects are genetic in origin.
What was "surprising" to the researchers was that women who moved to a new city between pregnancies were only half as likely to have a second child with a birth defect. Mothers whose first child had a defect were 11.6 times as likely to have a second child with a defect (compared to mothers whose first child did not have a defect), but if a mother moved to a new municipality between pregnancies, she was only 5.1 times as likely to have a second child with a defect. The researchers concluded, "[W]e find strong, if indirect, evidence ... suggesting that important environmental teratogens have yet to be discovered".
Exposure to pollutants
There is abundant scientific evidence that birth defects in laboratory animals and in humans have occurred as a result of exposure to five classes of pollutants: radiation, pesticides, metals (including mercury, cadmium, lead and others), solvents and dioxin-like chemicals including PCBs (polychlorinated biphenyls). From studies of pharmaceutical drugs found to cause birth defects, it is certain that other chemicals are teratogens as well.
Because municipal land fills and toxic waste dumps are laced with pesticides, toxic metals, solvents, dioxin-like compounds and sometimes even radioactive materials, at least seven studies have now reported finding unusually high numbers of birth defects in children born to parents residing near dumps.
The main reason why birth defects will continue to increase is that more than 500 new chemicals are introduced into commercial use each year. There will never be enough money available for independent scientists to conduct definitive (or even adequate) studies of all these chemicals to see if they cause birth defects in laboratory animals.
For ethical reasons, chemicals cannot be tested in any organised way on humans (though, contrarily, most people don't object to the experimental exposures that occur routinely in the workplace, and in the home via consumer products). In addition to 500 new chemicals appearing each year, more than 50,000 chemicals already in commercial use have never been tested for their ability to cause birth defects.
The prevailing US philosophy is that chemicals are innocent until proven guilty. Therefore, when new chemicals are released into the environment, the burden of proof rests on the public to show that damage has occurred before scientific studies are undertaken to describe the damage in detail. This philosophy guarantees that people must be harmed before study can begin.
Scientific studies can take years to complete. Even when an effect is grossly obvious, pinning down the cause can take a decade or longer. For example, mercury poisoned dozens of babies in the womb at Minamata, Japan, in 1955, but scientists did not clearly establish the cause for 15 to 18 years.
After research scientists are convinced, there is a long delay before the general public learns the facts, if it ever does.
Furthermore, the results of studies may not be clear-cut, for many reasons: it is difficult to measure exposure so usually a "surrogate" for exposure is used, such as place of residence, or occupation; many birth defect studies rely upon mothers recalling what chemical exposures occurred during their early months of pregnancy, and all such recollections are dubious; therefore it is difficult to rule out absolutely many possible causes of an observed effect.
No certainty
A society that demands scientific certainty before it will restrict the use of suspected teratogens guarantees that the rate of birth defects will continue rising. Scientific certainty about anything involving humans is, and will remain, elusive and rare.
Public health officials are reluctant to raise an alarm on less than 100% certain data. As a practical matter, an official will get in much more trouble for raising a false alarm about a suspected chemical than for making the opposite error (which allows birth defects to continue). Even well-justified alarm based on less than certain data draws an angry response from powerful moneyed interests.
On the other hand, allowing birth defects to continue will affect only one family at a time. Individual, unorganised victims do not threaten a public health official's job security.
When studies reveal that a particular chemical probably causes birth defects, the producers and users of the chemical typically conduct a lengthy campaign to deny and obscure what is known.
For example, the lead industry has known for at least 100 years that lead causes reproductive and developmental disorders in humans. But starting in 1925 medical doctors hired by the lead industry argued that lead occurs naturally in the human body and, therefore, the dangers of lead in petrol were not worth worrying about, much less studying. This strategy was persuasive to the public health community for 40 years.
The public health community relies almost exclusively on a decision-making technique that cannot take into account multiple exposures and cumulative effects, a technique called "risk assessment". At its best, risk assessment can provide a ballpark guesstimate of a few of the many hazards created by a single toxic chemical.
However, in real life we are all exposed to multiple chemicals all the time, and risk assessment cannot account for cumulative effects and multiple interactions. Heavy reliance upon such an unrealistic tool for decision-making leads to decisions that harm public health.
Finally, even the knowledgeable environmental community fails to fully adopt the clear requirements of a public health policy based on prevention of disease: persistent toxic pollutants must be banned. Over the last 20 years the US Environmental Protection Agency's lead policy has forced a mere 8% reduction in total US "consumption" of lead. At this rate it will take 3500 years for lead "consumption" to fall below 1000 pounds per year and thus disappear as a public health problem.
[From Rachel's Environment & Health Weekly (US).]