The environment can have an important influence on development, and this also includes the prenatal period. The growth that happens during the nine months of prenatal development is nothing short of astonishing, but this period is also a time of great vulnerability. Fortunately, the effects of many of these hazards can be greatly lessened or even avoided entirely. While dangers do exist, the vast majority of babies are born healthy.

Today, researchers understand a greater deal about teratogens, a term used to describe the broad range of conditions and substances that can increase the risk of prenatal problems and abnormalities.1 Teratogens can cause a wide range of problems from low birth-weight to brain damage to missing limbs. In order to minimize and avoid these dangers, it is essential to understand what poses a risk to the fetus and how such dangers can affect development.

Many diseases are capable of injuring a growing fetus. For example, doctors discovered that when a mother contracts rubella (also known as the German measles) early in her pregnancy, her child might suffer blindness, heart abnormalities, and brain damage as a result.2

In the past, doctors believed that the placenta served as a barrier to protect the growing fetus against toxins. During the 1960s, a number of pregnant women were prescribed the drug thalidomide which caused more than 10,000 infants to be born missing legs, arms, or ears. The birth defects caused by the drug made the dangers of certain medications very clear.3

Today, doctors recognize the teratogenic effects of many medicinal drugs including anticonvulsants, tetracycline, anticoagulants, bromides, and most hormones.

Because of the potential dangers, it is important for pregnant women to avoid any medications that have not been specifically recommended by their doctor. You have also probably noticed that most television ads for new medications include some type of statement warning that women who are pregnant or who may become pregnant should avoid taking the drug.

Fortunately, because doctors and mothers-to-be are far more aware of the potential dangers, the rates of medication-linked birth defects have been reduced considerably over the past few decades.

Prenatal damage caused by psychoactive drugs such as alcohol, cocaine, heroin, inhalants, and tobacco is still far too common. All psychoactive drugs have a deleterious effect on prenatal development leading to problems including low birth-weight, premature birth, and impaired brain development. The effects of such drug use can lead to both short-term and long-term deficits.4

Babies exposed to psychoactive drugs in-utero may show signs of drug withdrawal after birth, such as crying, startling, difficulty sleeping, and erratic eating. As they continue to develop and grow, these children may face learning problems such as an inability to pay attention, poor self-control, increased irritability, or even major developmental delays.

What impact can these psychoactive substances have on development?

• Tobacco use can result in low birth-weight as well as an increased risk of abnormalities such as urinary tract and limb malformations.
• Alcohol use during pregnancy causes fetal alcohol syndrome which is characterized by facial abnormalities including a smaller than average head size, a flattened nose, wide spacing between the eyes, and a narrow upper lip. Fetal alcohol syndrome also results in intellectual impairments, impaired physical growth, learning disabilities, and behavioral problems.

Fortunately, the effects of many environmental dangers can be minimized or even avoided entirely. Thanks to increased awareness of the effects of diseases, medications, and psychoactive substances, mothers are able to better ensure that they are healthy and free of harmful substances by the time they conceive a child.

While environmental dangers pose a definite risk to the growing fetus, they do not always cause harm. The impact of such hazards involves the interaction of a number of factors, including the timing of the exposure, the duration of the exposure, and possible genetic vulnerabilities that may be present.

The specific time of when the growing organism is exposed to the danger can play a major role in the ultimate outcome. Throughout prenatal development, there are times of greater susceptibility known as critical periods. For example, an embryo is most vulnerable to teratogens in the first eight weeks after conception. However, damage to major areas of the body including the brain and eyes can also occur during the later weeks of pregnancy.

In addition to abstaining from drugs, alcohol, medications, and other substances, proper medical care, social support, and postnatal care can all play an important role in minimizing the dangers of environmental toxins.