Prenatal Experience
Please note that this section contains my personal notes from my readings on this topic.
From Whats Going on in There? : How the Brain and Mind Develop in the First Five Years of Life
- Prenatal experience is important, to be sure, but if there is one feature that best characterizes life in the womb, it is the relative lack of stimulation. The womb, like a sturdy eggshell, is a highly protected environment: dark, warm, confining, and generally quieter than the outside world. This isolation seems to be just the right thing for early brain development, judging by the many problems that result when babies are born prematurely. (pages 40 -41)
- The womb is obviously the safest place for a fetus to develop in. Nor is its isolation the womb’s sole means of defense. According to one theory, the fatigue and nausea that many women suffer during early pregnancy are another means of protecting the embryo and young fetus. These symptoms peak during the baby’s most vulnerable phase, when all of its organs are first forming. Fatigue tends to keep a woman from risky physical activities, while “morning sickness” (a misnomer since it often lasts all day) tends to keep her diet bland, helping her to avoid natural toxins present in spoiled or exotic foods. Our best guess is that these symptoms are caused by the placental hormone human chorionic gonadotropin (HCG). This hormone can be detected in the mother’s blood as early as one week after conception… Miserable though it can be, morning sickness is actually regarded as a good sign in pregnancy, because it means that the placenta is developing well; several studies have found that women experiencing nausea are less likely to miscarry than those who don’t. (page 41)
- By this standard, a mom throwing up twice a day and who can barely stay awake in the afternoon is a good start. But while the placenta is trying, in this way, to protect the fetus from harmful influences in the environment, it is unfortunately not foolproof. The womb is isolated but by no means wholly immune from the outside world. Almost every drug, hormone, metabolite, infectious agent, or other chemical that makes its way to the mom’s bloodstream will cross the placenta in some measure. (page 42)
- Ever since the thalidomide disaster in the 1960s, women have become aware that exposure to various agents can harm their developing fetus. Those that have been documented to cause fetal malformations in a statistically significant number of cases are known as teratogens. It is surprisingly difficult to prove, however, that a particular agent is a teratogen, because its effects must always be compared to the baseline risk for any birth defect, which is disturbingly high. Overall, two or three of every hundred babies born has some kind of defect that will affect their appearance, development, intellect, or ability to function. Compare that to the risk of thalidomide, one of the worst teratogens ever identified, which causes limb and other malformations in about 20% of fetuses exposed during the first trimester. Even with known teratogens, it’s a probability game, making it difficult to know for certain whether a particular defect was caused by that specific agent or was simply a result of the generally high odds for any sort of defect. (page 42)
- The fact is that most birth defects — an estimated 65% — occur without any identifiable cause. Another 20% to 25% can be attributed to recognized defects in chromosomes or genes, but only some of these are inherited; the others occur spontaneously. Known environmental or disease agents are responsible for no more than 10% of all defects. (page 42)
- Teratogens are likelier to have more devastating effects on the fetus during the first three to four months of pregnancy, when the different organ systems are all forming. (page 42)
- Many teratogens act cumulatively; so even if the risk of any one exposure is quite low, exposure to several agents or risk factors can multiply the overall risk to the fetus. (Smoking, for instance, is known to increase fetal susceptibility to many other teratogens.) Since every woman faces a slightly different combination of risk factors, “better safe than sorry” is, again, a wise way to protect the public at large. (page 43)
- As we’ve noted, the vast majority of potential teratogens have barely been studied. Therefore, women who work in factories, farms, hospitals, laboratories, beauty parlors, dry cleaners, and any other job with daily chemical exposure need to be especially careful during pregnancy, to learn as much as possible about the substances in their work environment, and to minimize their exposure to anything suspect. (page 63)
Based on what is known, exposure to the following chemicals should be avoided during pregnancy: organic solvents (including toluene, benzene, and gases used in anesthesia), oil-based paints (latex and other water-based paints are safe), all types of herbicides and pesticides, PCBs (which were banned in the United States in the 1970s but remain concentrated in many landfills, as well as in lakes and the fish that inhabit them), vinyl chloride (used in plastic manufacturing), carbon monoxide, hydrocarbons (including gasoline), mercury compounds (particularly methyl mercury, which is used as a fungicide), and other heavy metals including cadmium (present in cigarette smoke), nickel, and lead.
The greatest risk occurs if a teratogen is inhaled or ingested, so volatile compounds, such as solvents and oil-based paints, should be handled in a well-ventilated area, and hand-to-mouth contact should be avoided when using any kind of chemical. Volatile teratogens have most clearly been linked to birth defects in the case of solvent abusers — pregnant women who regularly sniff toluene to get high. The data are less convincing for women exposed to solvents in their jobs, although studies do suggest that hairdressers, operating room doctors and nurses, and certain factory workers are somewhat likelier to miscarry or to have children with birth defects or developmental delays than women without such exposure. As compared to occupational levels, the occasional exposure to volatile teratogens, like pumping your own gas or painting the baby’s room with oil-based paint, is highly unlikely to harm the fetus.
The information contained throughout this blog / website should not be used as a substitute for the medical care and advice of your pediatrician / physician.
