In addition to these self-reported symptoms of
pregnancy, an obstetrician can use ultrasonography
to definitively identify an early gestation. Using trans-
vaginal ultrasound techniques, an obstetrician can
identify a gestational sac as early as two weeks, al-
though four to five weeks is the norm. A yolk sac can
be seen as early as three weeks but should be clearly
seen by six weeks. At seven weeks, the earliest picture
of the developing fetus, known as the fetal pole, can
be detected. By eight weeks, the fetal heart can be
seen contracting. From this gestational age to about
twelve weeks, the size of the fetus, measured from the
top of the head to the hips (the crown-rump length),
can be compared with the gestational age based on a
woman’s last menstrual period. These two measures
are used to determine the gestational age of the preg-
nancy and to predict the pregnancy’s due date.
As the pregnancy progresses, the uterus contin-
ues to enlarge. By twelve weeks of gestation, the uter-
us becomes perceptible through the abdominal wall.
This is usually noticed as a small lump that protrudes
from the lower abdomen, slightly above the pelvic
bone (pubic symphysis) at the level of the start of
pubic hair growth. Starting at twenty weeks, a mea-
surement is regularly taken from the pubis to the top,
or fundus, of the uterus during an obstetrical visit.
The bladder must be empty to produce an accurate
measurement. The resulting measurement in centi-
meters should roughly equal the number of weeks of
pregnancy, with an error of plus or minus two centi-
meters. This measurement, called the fundal height,
may indicate that the fetus is not growing properly
(i.e., is too small or too big). If an abnormal result is
obtained, an ultrasound can usually be done to check
fetal growth and the level of amniotic fluid in the
womb. This general principle is applicable to single
fetal gestations only, because twins and other multiple
pregnancies necessarily produce a larger fundal
height.
In addition to these changes in physical stature,
the pregnant woman goes through a series of amaz-
ing physiologic changes that affect all aspects of the
maternal body. From a metabolic perspective, preg-
nancy necessitates an increased maternal need for nu-
trients, water, and energy (calories). The fetus is
dependent on the expectant mother for all nutrition-
al needs and oxygenation, and it extracts what it
needs at the woman’s expense. Thus, the woman her-
self needs to gain weight and increase her caloric con-
sumption to meet her own needs and those of the
fetus. The National Research Council’s dietary guide-
lines recommend that pregnant women increase their
caloric intake by approximately 300 kilocalories per
day. Specifically, a nonpregnant woman requires ap-
proximately 2,200 kilocalories per day. A pregnant
woman should thus consume 2,500 kilocalories per
day.
The demand for iron also increases during preg-
nancy. The body uses iron to carry oxygen in the
blood, which is ultimately transported to the fetus.
Thus, it is recommended that women increase their
iron intake, especially during the second and third
trimesters, when the fetus does the bulk of its growing
to reach its physical size. Usually, adequate amounts
of iron can be obtained through ingestion of iron rich
foods, such as liver, and dark leafy vegetables, such as
spinach. Some sources have found, however, that the
amount of iron provided by both normal dietary in-
take and maternal storage is insufficient to meet
pregnancy demands. In fact, the National Academy
of Sciences and the American College of Obstetrics
and Gynecology recommend that pregnant women
receive a supplement of 30 milligrams of iron per
day. Most obstetricians recommend that a woman stay
on her prenatal vitamin, which should supply enough
iron to cover the recommended amount. It is also
common practice to check the level of blood (via the
hematocrit and hemoglobin tests) both at the start
and in the third trimester of pregnancy. If the expec-
tant mother is found to be anemic, she is started on
additional iron supplements (ferrous sulfate tablets).
In addition to the increased demand for nutri-
ents, increasing the intake of water is vital to the
maintenance of pregnancy. Higher levels of total
body water are required to provide the increased fluid
volume needed to meet the demands of increased
blood flow and circulation to the developing baby.
Thus, the pregnant woman’s kidney system begins to
retain water. Maintaining adequate amounts of fluid
intake is also important, as it is easier for pregnant
women to become dehydrated, which can lead to pre-
term contractions.
The summation of all these dietary and metabolic
changes can be seen in the recommendations for
weight gain in pregnancy. In a normal nonobese
woman, a twenty-five to thirty-five pound weight gain
is recommended. This value fluctuates depending on
the prepregnancy weight of a woman; specifically, an
underweight woman may gain up to forty pounds,
while it is recommended that overweight women limit
their weight gain to fifteen to twenty pounds. Usually,
three to six pounds are gained in the first trimester,
with a subsequent gain of one-half to one pound per
week thereafter until term. Weight should be mea-
sured at every obstetrical visit. If a woman does not
show a ten-pound weight gain by the mid-second tri-
mester, her nutritional status should be reviewed. A
woman with below average weight gain is at higher
risk of producing a low-birthweight and intrauterine
growth-restricted infant. Likewise, obese womenPREGNANCY 319