Development anD aging 345Like many other drugs, alcohol crosses the placenta
and affects the fetus. Fetal alcohol syndrome (FAS) is a
constellation of defects that can result from alcohol use by
a pregnant woman. Babies born with FAS typically have
a smaller than normal brain and head, facial deformities,
poor motor coordination, and, sometimes, heart defects
(Figure 17.20). The symptoms can’t be reversed, and FAS
children never catch up physically or mentally. Between
60 and 70 percent of alcoholic women give birth to infants
with FAS. Many doctors urge near or total abstinence from
alcohol during pregnancy.
A pregnant woman who uses cocaine, especially crack,
prevents her child’s nervous system from developing nor-
mally. As a result, the child may be chronically irritable as
well as abnormally small.
Research evidence suggests that tobacco smoke reduces
the level of vitamin C in a pregnant woman’s blood, and in
that of her fetus as well. Cigarette smoke also harms the
growth and development of a fetus in other ways. A preg-
nant woman who smokes daily will give birth to an under-
weight newborn even if her own weight, nutrition, and all
other relevant variables are the same as those of pregnant
nonsmokers. As noted at the beginning of this section, a
pregnant smoker also has a greater risk of stillbirth, as well
as of miscarriage and premature delivery. No one knows
just how cigarette smoke damages a fetus. However, its
demonstrated effects are additional evidence that the pla-
centa cannot protect a developing fetus from every danger.defect called spina bifida (“split spine”) may develop, in
which the neural tube doesn’t close and separate from the
ecto derm. The infant may be born with part of its spinal cord
exposed inside a cyst. Infection is a serious danger, and the
resulting neurological problems can include poor bowel and
bladder control. To prevent neural tube defects, folic acid now
is added to wheat flour and other widely used foods.
A pregnant woman must eat enough to gain between
20 and 35 pounds, on average. If she gains much less than
that, she may be putting her fetus at risk. Infants who are
severely underweight have more complications after deliv-
ery. As birth approaches, the growing fetus demands more
and more nutrients from the mother’s body. For example, a
fetus’s brain grows the most in the weeks just before and
after birth. Poor nutrition during that time, especially pro-
tein deficiency, can have repercussions on intelligence and
other brain functions later in life.
Infections present serious risks
A pregnant woman’s IgG antibodies cross the placenta.
They can help protect her developing infant from all but
the most severe bacterial infections. Other teratogens—
agents that can cause birth defects—are more serious
threats. Some viral diseases can be dangerous during the
first 6 weeks of pregnancy, when the organs of a fetus are
forming (Figure 17.19). For example, if a pregnant woman
contracts rubella (German measles) during this time, there
is a 50 percent chance that some organs of the embryo won’t
form properly. If she contracts the virus when the embryo’s
ears are form ing, her newborn may be deaf. With time, the
risk of damage diminishes, and getting vaccinated before
pregnancy can eliminate the risk altogether.
Drugs of all types may do harm
During its first trimester in the womb, an embryo is
extremely sensitive to drugs the mother takes. In the 1960s
many women using the tranquilizer tha lidomide gave
birth to infants with missing or deformed arms and legs.
Although it wasn’t known at the time, thalidomide alters
the steps required for normal limbs to develop. When the
connection became clear, thalidomide was withdrawn
from the market (although it now has other medical uses).
Other commonly used tranquilizers, as well as some
sedatives and barbiturates, may cause similar, although
less severe, dam age. Anti-acne drugs such as retinoic acid
increase the risk of facial and cranial deformities. The
antibiotic streptomycin causes hearing problems and may
adversely affect the nervous system. A pregnant woman
who uses the antibiotic tetracycline may have a child
whose teeth are yellowed.
Figure 17.20 Fetal alcohol syndrome may cause mental
retardation. Outward symptoms are low and prominent ears,
poorly developed cheekbones, and a long, smooth upper lip.
The child may have growth problems and abnormalities of the
nervous system.© George SteinmetzCopyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).