Vulnerability of the Fetus

An earlier post discussed general factors in the health of a developing baby. (See “The First Stage of Life: Vigilance Required,” December 15, 2010.) This article goes deeper.

The Wikipedia article Environmental Toxins and Fetal Development describes hazards to a developing baby. “Historically, it was recognized that certain infections or poisons that were harmful to the pregnant woman often were as harmful, or more harmful, to the fetus. Infectious syndromes such as congenital rubella (German measles) and congenital syphilis were examples. In the last century evidence emerged that certain environmental exposures that were not obviously harmful to the mother could cause serious harm to the fetus.

Substances called persistent organic pollutants (POPs) include several chemicals that are known to have adverse effects on fetal development: polychlorinated biphenyls, dioxins, furans, and insecticides such as DDT. Some environmental toxins known as endocrine disruptors have adverse effects on fetal development. Processes involved with differentiation and growth of embryonic and fetal cells are under the tight control of a myriad of messaging systems, some of which involve hormones. In particular, chemicals that mimic or otherwise disrupt the normal response to estrogen, androgen, or thyroid hormone have been particularly of concern during fetal development. Environmental carcinogens also are of concern during this time. Research has indicated that in-utero exposure to carcinogens may confer much higher risks later in life.”

The period when the developing baby is most sensitive to foreign/toxic chemicals is between the end of the first week, when the fertilized egg is implanted in the lining of the uterus and the life of the tiny embryo begins, and the end of the eighth week when the embryo’s organs are all formed and the growth of the fetus (now called) begins. The embryonic stage (when it is less than half an inch long) may be the most sensitive to damage by toxic chemicals because it is during this time when the critical differentiation of cells into all the major tissue types (e.g., organs, muscles, bones) is occurring.

Tracey Woodruff, Director of Reproductive Health and the Environment at the University of California San Francisco, recently reported on a detailed study of chemicals in pregnant women.* Of 163 chemicals studied, 43 were found in virtually all 268 pregnant women in the study. A metabolite (break-down product) of DDT was found in virtually all the women, even though DDT was banned in 1972! PCBs, PBDEs, phthalates, perfluorinated compounds, BPA and Triclosan were found in 99 to 100 percent of the women.

This study, plus two by the Center of Disease Control,** found the following levels of toxic chemicals:

  • PFOA 4 ppb in serum***
  • PFOS 20 ppb in serum
  • Triclosan 17 ppb in urine
  • BPA 2-3 ppb in urine
  • Methyl ethyl phthalate (a breakdown product of common plasticizers of vinyl products) 226 ppb in urine
  • DDE (a breakdown product of DDT) 2 ppb in serum, but 150-300 ppb in blood lipids

To understand the significance of these numbers we can compare them with levels of hormones in the blood. There are more than 50 hormones (produced by nine endocrine glands and other organs) that regulate all chemical processes in the body. A typical analysis of serum gives the following results:

  • Free thyroxine: ~1 ppb
  • Epinephrine: 1 ppb
  • Parathyroid: less than 1 ppb
  • ACTH: less than 0.2 ppb.

We can see that the levels of toxics in pregnant women’s serum and urine are greater than the levels of these four hormones, and the level of DDE is much greater in the serum lipid fraction (which contains fat-soluble things such as vitamins A, D, E and K, and several steroids). This is surely not a good omen!

A mother who births a child with medical defects (many of which will not show up until later years) will naturally wonder how the defects could have occurred even though she had been very careful about her diet and health during pregnancy and lactation period. She will often attribute them to genetic defects. The truth is more complicated, and some scientists believe that many birth defects are due to toxic substances in the mother during her pregnancy and during the time she is breast-feeding the baby. The ancient U.S. Toxic Substances Control Act (TSCA) must be revised for present conditions, so that people – especially mothers – are not exposed to substances that can damage the health of their children. Revision of TSCA is now before Congress.


* San Francisco Chronicle, 14 January, 2011 and Environ Health perspect: – doi:10.1289/ehp.100272

** CDC 3rd and 4th Reports on National Exposures to Environmental Chemicals

*** Serum is blood in which red and white cells have been removed.

About donlouis

The author has long had a keen interest in staying healthy and fit, and in doing whatever I can to keep the natural environment unpolluted and a healthy space for people and all animals. As a Board Member of a municipal water district, I regularly deal with the issue of water quality. I first became aware of radiation hazards from toxic materials while working on uranium for nuclear reactors. During the 1960s I was tuned into the global hazard from Strontium 90 raining down from atmospheric testing of nuclear bombs. While working in the chemical industry in later years I became aware of the many forms of chemical contaminants entering the environment every day, and resolved to do something about it. I am able to make sense out of the voluminous descriptions of common toxic chemical because of my training in chemistry, with a Ph.D. degree and several decades of research and development work in the chemical industry. My training and experience enables me to present to readers reliable and current information on the topic of chemical hazards in the environment, and their threats to human health. All my life I have loved hiking and camping in nature. Skiing, river kayaking, and tennis have been my favorite physical activities. Nature photography is my artistic passion.
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