Chapter 4: Risk Reduction Pages 97-107

The scientific study of birth defects is called terantology The scientific study of birth defects is called terantology. Harmful agents that can cause birth defects, called teratogens, include: -viruses -drugs -chemicals -pollutants -stressors -malnutrition

Substances that impair the child’s action and intellect by harming the brain are called behavior teratogens. Approximately 3 percent of all fetuses are born with major structural anomalies and 10-20% with behavioral difficulties related to prenatal care.

Teratology is a science of risk analysis, which attempts to evaluate the factors that can make prenatal harm more or less likely to occur. Three crucial factors that determine whether a specific teratogen will cause harm, and of what nature, are: -the timing of exposure -the amount of exposure -the developing organism’s genetic vulnerability to damage from the substance

The time when a particular part of the body is most susceptible to teratogenic damage is called its critical period. For physical structure and form, this is the entire period of the embryo. However, for behavioral teratogens, the entire prenatal period is critical.

Some teratogens have a threshold effect – that is, the substances are harmless until exposure reaches a certain frequency or amount. However, the interaction of some teratogens when taken together may make them more harmful at lower dosage levels than when taken separately.

Genetic susceptibilities to the prenatal effects of alcohol and to certain birth disorders, such as cleft palate, may involve defective enzymes. When the mother-to-be’s diet is deficient in folic acid, neural-tube defects such as spina bifida or anencephaly may result.

Genetic vulnerability is also related to the sex of the developing organism. Generally, male embryos and fetuses are more vulnerable to teratogens. This sex not only has a higher rate of teratogenic birth defects and later behavioral problems, but also a higher rate of spontaneous abortions, and older members of this sex have more learning disabilities.

It was once believed that a pregnant woman’s placenta prevented all harmful substances from reaching the fetus. This belief was proven wrong when ad epidemic of rubella led to an increase in babies who were born deaf, and an increase in newborns with deformed limbs was traced to maternal use of the drug thalidomide.

The most devastating viral teratogen is the human immunodeficiency virus (HIV), which gradually overwhelms the body’s immune system and leads to AIDS. Babies who are infected with this virus usually die by age 5.

Pregnant women who are HIV-positive can reduce the risk of transmitting the virus to their newborns by giving birth by cesarean section, by not breast-feeding, and by taking antiretroviral drugs.

State three reasons why almost a million HIV-positive children continue to be born each year:

-may not be aware that they have the disease -drugs for treating HIV are very expensive -socioculture prevents woman from admitting she has the disease

The most common teratogen in developed nations is alcohol The most common teratogen in developed nations is alcohol. High doses of this teratogen cause fetal alcohol syndrome, and less intense doses cause fetal alcohol effects. The damage is increased when alcohol is combined with other psychoactive drugs.

Newborns who weigh less than 5 ½ pounds are classified as low-birthweight babies. Below 3 pounds, they are called very-low-birthweight babies. At less than 2 pounds they are extremely low-birthweight babies. Worldwide, rates of this condition vary from nation to nation.

Babies who are born 3 or more weeks early are called preterm Babies who are born 3 or more weeks early are called preterm. Infants who weigh substantially less than they should, given how much time has passed since conception, are called small for gestational age.

About 35% of all low-birthweight (LBW) births in the United States are linked to maternal use of tobacco. Two other common reasons for low birthweight are maternal illness and malnutrition.