BOX21–3 CONGENITAL FETAL INFECTIONS
Congenital syphilis—syphilis is a sexually trans-
mitted disease caused by a bacterium (Treponema
pallidum). These bacteria may cross the placenta after
the fourth month of gestation. Consequences of
early infection of the fetus are death, malformations
of bones and teeth, or cataracts. If infection occurs
toward the end of gestation, the child may be born
with syphilis. This is most often apparent as a rash on
the skin and mucous membranes. Syphilis in adults
can be cured by penicillin; prevention of congenital
syphilis depends upon good prenatal care for
women who may be infected. The Centers for
Disease Control and Prevention has a goal of eradi-
cating syphilis in the United States, which would
eliminate fetal infection.
Congenital toxoplasmosis—this condition is
caused by the protozoan parasite Toxoplasma
gondii. For most healthy people, toxoplasmosis has
no symptoms at all; it is a harmless infection.
Because cats and some other mammals are hosts
for this parasite, pregnant women may acquire
infection from contact with cat feces or by eating
rare beef or lamb. Consequences for the fetus are
death, mental retardation, or blindness. Retinal
infection may only become apparent during child-
hood or adolescence. Prevention now depends
upon education of pregnant women to avoid
potential sources of infection.A teratogen is anything that may cause develop-
mental abnormalities in an embryo-fetus. Several
infectious microorganisms are known to be terato-
genic; they may cross the placenta from maternal
blood to fetal blood and damage the fetus.
Congenital rubella syndrome—the virus of
German measles (rubella) is perhaps the best
known of the infectious teratogens. If a woman
acquires rubella during pregnancy, there is a 20%
chance that her fetus will be affected.
Consequences for the fetus may be death (still-
birth), heart defects, deafness, or mental retarda-
tion. Women who have never had rubella should
consider receiving the vaccine before they begin to
have children. In this way, congenital rubella syn-
drome is completely prevented. Use of the rubella
vaccine has made this syndrome rare in the United
States, but many developing nations do not have
extensive vaccination programs.
Congenital varicella syndrome—chickenpox
(herpes zoster) is a viral disease that most people
have during childhood. If a pregnant woman
acquires chickenpox, however, the virus may cross
the placenta. Consequences for the fetus include
malformed limbs, cutaneous scars, blindness, and
mental retardation. This is not a common congeni-
tal syndrome, and the success of the chickenpox
vaccine should make it truly rare.16 weeksPlacentaUterusUmbilical cordCervix
VaginaFigure 21–4. Fetal development at 16 weeks.
QUESTION:Name the fluid that surrounds the fetus, and
state its function.
days), with a range of 37 to 42 weeks (see Box 21–5:
Premature Birth). Toward the end of gestation, the
placental secretion of progesterone decreases while
the estrogen level remains high, and the myometrium
begins to contract weakly at irregular intervals. At this
time the fetus is often oriented head down within the
uterus (Fig. 21–6). Labor itself may be divided into
three stages:
First stage—dilation of the cervix. As the uterus con-
tracts, the amniotic sac is forced into the cervix,
which dilates (widens) the cervical opening. At the
end of this stage, the amniotic sac breaks (rupture
of the “bag of waters”) and the fluid leaves through
the vagina, which may now be called the birth
canal. This stage lasts an average of 8 to 12 hours
but may vary considerably.
Second stage—delivery of the infant. More power-
ful contractions of the uterus are brought about
by oxytocin released by the posterior pituitary
gland and perhaps by the placenta itself. This stage
may be prolonged by several factors. If the fetus is
positioned other than head down, delivery may be483