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Antenatal Evaluation
of the IUGR Fetus
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Serial ultrasound evaluation of growth of fetal body proportions
and Doppler velocimetry assessment of uterine, placental, and fetal
circulations are the standard diagnostic approaches used to determine
the severity of intrauterine growth restriction, detect deteriorating
fetal physical condition, and predict impending fetal death. Chronic
fetal distress resulting from placental insufficiency, hypoxia, and
ischemia, with or without acidosis, is associated with increased
Doppler arterial waveform amplitudes in the fetal peripheral vasculature
that indicate increased vascular resistance and reduced blood flow
to fetal tissues and the placenta. Various ratios of systolic-to-diastolic
flow velocity (amplitude) waveforms have been used to detect decreased peripheral
blood flow in the fetus, including the systolic-to-diastolic ratio:
(systolic – diastolic)/systolic ratio (resistance
index) or (systolic – diastolic)/mean ratio (pulsatility
index). The most severely affected IUGR fetuses with the greatest
risk of death demonstrate absent or reversed diastolic flow in their
systemic arteries, with increased umbilical venous pulsation and
reversed flow in the abdominal vena cava. Because of associated
fetal hypoxemia, which causes vasodilation of certain vital organs
such as the brain, some of these fetuses can have increased cerebral
or internal carotid artery flow velocities and cerebral blood flow
rates. Such conditions have been hypothesized to help maintain brain
growth. Doppler waveform abnormalities usually precede less specific
signs of fetal distress such as abnormal changes in fetal heart
rate that occur spontaneously under basal conditions or in response
to increased uterine contractions during oxytocin challenge testing.
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General Evaluation and
Treatment in the Delivery Room
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SGA infants lose heat rapidly because of their large surface
area relative to body weight and their scant subcutaneous insulation.1,7,9 To prevent
hypothermia, they should be dried quickly and completely, placed
under a radiant warmer, and protected from drafts with warmed blankets.
Severely undergrown SGA infants often experience marked oxygen and substrate
deprivation in utero, which can lead to cardiopulmonary failure
at birth. Close to term, they can present with meconium aspiration
syndrome and exhibit signs of acute and chronic hypoxia, including
hypotension, metabolic and respiratory acidosis, and persistent pulmonary
hypertension.
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Markedly SGA infants who have severe intrauterine growth restriction
usually have disproportionately large heads relative to their undergrown
trunks and extremities. Their abdomen can appear shrunken or “scaphoid,” and
they must be distinguished from infants with diaphragmatic hernias,
who also present with respiratory distress. Their extremities appear
scrawny, with thin skin folds and decreased amounts of subcutaneous
fat and skeletal muscle. The skin is loose and often rough, dry,
and peeling. In term and postterm infants who are markedly small
for gestational age, the fingernails can be long, and the hands and
feet tend to look large for the size of the body. The face often
appears shrunken or “wizened.” Cranial sutures
can be widened or overriding. The anterior fontanel often is larger
than expected, representing diminished membranous bone formation.
The umbilical cord often is thin, and when meconium has been passed
in utero, the cord, nails, and skin may have a yellow or green discoloration. SGA
infants also have an increased incidence of severe malformations
and chromosomal abnormalities accompanied by dysmorphic features
and congenital anomalies, “funny-looking facies,” abnormal
hands and feet, and the presence of palmar creases. SGA infants with
congenital infections can have ocular disorders such as chorioretinitis,
cataracts, glaucoma, and cloudy cornea plus hepatosplenomegaly,
jaundice, and a “blueberry-muffin” rash, which
represents subcutaneous accumulations of extramedullary hematopoiesis.
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Gestational age assessment using physical criteria often is erroneous
in infants who are small for gestational age. Vernix caseosa frequently
is reduced or absent; thus, the skin more readily desquamates, and
sole creases appear more prominent and thus more mature because
of increased wrinkling from greater exposure to amniotic fluid.
Breast tissue formation also is reduced, and the female external
genitalia appear less prominent because of decreased perineal adipose
tissue covering the labia. Specific organ maturity often continues at
normal developmental rates despite diminished somatic growth; thus,
cerebral cortical convolutions, renal glomerular development, and
alveolar maturation correlate better with gestational age than with
body size.
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SGA infants often appear to have advanced neurological maturity,
although this observation is derived primarily from comparisons with
infants of similar birth weight rather than similar gestational
age.3 Active and passive tone and posture are usually
normal in SGA infants and are reliable guides to gestational age
unless there are other factors (eg, serious central nervous system
disorders that could alter tone). SGA infants often have a “hyperalert” appearance,
generally look “starved and hungry,” and often
are described as jittery and hypertonic, even without simultaneous
hypoglycemia. They can be hyperexcitable but show mixed aberrations
in tone, from hypotonia to hypertonia. When intrauterine growth restriction
is severe, SGA infants tend to show abnormal sleep cycles and diminished
muscle tone, decreased deep tendon and facial tactile reflexes,
and general physical inactivity and apathy. These neurological abnormalities
usually reflect brain injury during fetal development.