1082
UNIT 5
Continuity
28
Anatomical Changes
As pregnancy progresses, the female reproductive organs be-
come increasingly vascular and engorged with blood, and the
vagina develops a purplish hue (
Chadwick’s sign
). Te enhanced
vascularity increases vaginal sensitivity and sexual intensity,
and some women achieve orgasm for the first time when they
are pregnant. Prodded by rising levels of estrogen and proges-
terone, the breasts enlarge and engorge with blood, and their ar-
eolae darken. Some women develop increased pigmentation of
facial skin of the nose and cheeks, a condition called
chloasma
(klo-az
9
mah; “to be green”) or the “mask of pregnancy.”
Te degree of uterine enlargement during pregnancy is re-
markable. Starting as a fist-sized organ, the uterus fills most of
the pelvic cavity by 16 weeks
(Figure 28.16a, b)
. Tough the
fetus is only about 140 mm long (crown-to-rump) at this time,
the placenta is fully formed, uterine muscle is hypertrophied,
and amniotic fluid volume is increasing.
As pregnancy continues, the uterus pushes higher into the
abdominal cavity, exerting pressure on both abdominal and pel-
vic organs (Figure 28.16c). As birth nears, the uterus reaches the
level of the xiphoid process and occupies most of the abdominal
cavity (Figure 28.16d). Te crowded abdominal organs press su-
periorly against the diaphragm, which intrudes on the thoracic
cavity. As a result, the ribs flare, causing the thorax to widen.
Te increasing bulkiness of the anterior abdomen changes
the woman’s center of gravity, and many women develop
lor-
dosis
(accentuated lumbar curvature) and backaches during
the last few months of pregnancy. Placental production of the
hormone
relaxin
causes pelvic ligaments and the pubic sym-
physis to relax, widen, and become more flexible. Tis increased
flexibility eases birth passage, but it may result in a waddling
rapid growth of the body structures that were established in the
embryo. During the first half of this period, cells are still dif-
ferentiating into specific cell types to form the body’s distinctive
tissues and are completing the fine details of body structure. Te
main events of the fetal period—weeks 9 through 38—are listed
chronologically in
Table 28.1
on p. 1084. Te greatest amount
of growth occurs in the first 8 weeks of life, when the embryo
grows from one cell to a fetus of 1 inch.
Check Your Understanding
14.
When does the fetal period begin?
For answers, see Appendix H.
Effects of Pregnancy
on the Mother
Describe functional changes in maternal reproductive
organs and in the cardiovascular, respiratory, and urinary
systems during pregnancy.
Indicate the effects of pregnancy on maternal metabolism
and posture.
Te mean duration of pregnancy is 38 weeks from the time
of ovulation to birth. Pregnancy can be a difficult time for the
mother because profound adaptations occur in several body
systems. Not only are there anatomical changes, but striking
changes in her metabolism and physiology occur to support the
pregnancy and prepare her body for delivery and lactation.
(a) Before conception
(Uterus the size of a fist
and resides in the pelvis.)
(b) 4 months
(Fundus of the uterus is
halfway between the
pubic symphysis and
the umbilicus.)
(c) 7 months
(Fundus is well above
the umbilicus.)
(d) 9 months
(Fundus reaches the
xiphoid process.)
Figure 28.16
Relative size of the uterus before conception and during pregnancy.
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