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T. Yang et al.
Table 2.2 NT and NB value of normal fetuses during 11 to 14weeks of gestation
NT
Gestation (week)
11 1252 0.995 0.333 329 1.969 0.474
12 2435 1.189 0.358 656 2.003 0.465
13 2227 1.331 0.371 564 1.995 0.458
14 1043 1.378 0.396 255 2.048 0.486
Note: The data are from the West China Second Hospital of Sichuan University
n (number) X(mm) SD(mm) n(number) X(mm) SD(mm)
NB
Fig. 2.11 Fetal NT.Measurement of NT at 12+3weeks of gestation
Fig. 2.12 Fetal nasal bone. Measurement of NB at 12+ 3 weeks of
gestation
Fig. 2.13 Abnormal echo of fetal nasal bone. Thickened fetal NT with
absent nasal bone at 12+6weeks of gestation.
magna can be observed. Color Doppler ow shows the cerebral vessels of the fetus (Figs.2.15 and 2.16).
Ultrasound Image oftheFetal Face
After 11weeks of gestation, the fetal maxillofacial bones are
gradually visible. Under appropriate scanning angle in the
context of amniotic uid, fetal eyes, nose, lips, philtrum,
face, upper alveolar bone, lower alveolar bone, ears, scalp,
and hair can be observed through a systematic evaluation in
the coronal and sagittal views (Fig.2.17).
Images oftheFetal Spine
The hyperechoic vertebrae show regular “string-bead” in
parallel arrangement on sagittal view. The sacrococcygeal
region slightly tilts backward and expands in the lumbar
section. The vertebrae distribute as a triangle on a trans-
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2 Application ofDiagnostic Ultrasound inthePerinatal Period
33
Fig. 2.14 Screening of essential structures in early pregnancy. (a).
Transverse view of the fetal head at 13 weeks of gestation; (b).
Transverse view of fetal chest: spectrum Doppler of fetal tricuspid
valves; (c). Transverse view of the fetal stomach in abdominal level;
(d). Transverse view of fetal bladder showing bilateral umbilical arter-
ies; (e). Fetal omphalocele at 13weeks of gestation, showing the umbilical cord inserting into the abdominal cavity on one side of the bulging
area; (f). Holoprosencephaly at 13weeks of pregnancy; (g). Fetal lower
limbs at 12weeks of gestation; (h). Fetal upper limbs at 12 weeks of
gestation
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Fig. 2.14 (continued)
T. Yang et al.
Fig. 2.15 Fetal head. (a). Transverse view of the fetal head presenting
hyperechoic ring structure; (b). Transverse view of the fetal head showing fetal brain structure: midline and thalamus; (c). Transverse view of
the fetal head presenting the complete and smooth ring echoic structure.
The septum pellucidum and thalamus are showed; (d). Transverse view
of fetal head showing anterior horns of the lateral ventricles; (e).
Transverse view of fetal head showing cerebellum; (f). Intracranial choroid plexus of the fetus; (g). The lateral ventricle of the fetus
2 Application ofDiagnostic Ultrasound inthePerinatal Period
35
g
Fig. 2.15 (continued)
Fig. 2.16 Fetal intracerebral vessels. The cranial base view of Fetal
Willis artery ring
vessels, trachea, lungs, esophagus, and so on. The heart
located in the left chest cavity, with the apex pointing to the
left. The left and right ventricles and atria are of the same
size. Multiple hyperechoic ribs in an oblique arrangement
are visible after 11 to 12weeks of gestation. During the third
trimester, the echo of fetal ribs is becoming visualized. The
fetal lung is of moderate echo with a smooth edge in the
second and third trimesters. It does not squeeze the heart and
is clearly displayed with the liquid background (Figs.2.20
and 2.21).
Images oftheFetal Abdomen
The liver, located in the right upper fetal abdomen, presents homogeneous isoecho (as shown in the Fig. 2.22).
The fetal umbilical vein inserts into the abdominal cavity
in the midline of the fetal abdominal wall. It divides into
two branches, one joins the portal system to the liver substance and the other connects to the inferior vena cava
through the ductus venous. The umbilical cord inserts into
the abdominal wall, as shown in the Fig.2.22. The gallbladder, in the same view with the umbilical vein, is visible after 24 weeks of gestation. The fetal stomach is
anechoic in the left side of the abdominal cavity (as shown
in the Fig.2.22). After 20weeks of pregnancy, digestive
tract malformation should be considered if there is an
absent fetal stomach combined with hydramnios, and
repeated examination should be carried out 30 to 45minutes later. Multiple anechoic bowel loops are evident in
the fetal abdominal cavity during the second and third trimesters of pregnancy (as shown in the Fig.2.22). With the
development of a pregnancy, meconium thickens, followed by gradually increased bowel echo (Fig.2.22).
verse view, and the spinal canal is visible as strip-like
anechoic area. The centrum is the ossication center of the
vertebral body. On the coronal view, the spine appears as
three parallel hyperechoic lines near the ventral side
(Figs.2.18 and 2.19).
Ultrasound Images ofFetal Thorax
The fetal chest cavity is composed of spine, ribs, and sternum. Main organs in the fetal chest are the heart, large blood
Images ofFetal Genitourinary Tract
After 16weeks of pregnancy, the fetal kidneys are visible by
the longitudinal and transverse view of transabdominal ultrasound. Fetal kidneys, showing as a circular or ovoid-shaped
hypoecho, located lateral to the fetal spine. Echo of the renal
capsule and collecting system is enhanced. The fetal bladder
is a round cystic structure, the size of which varies during
dynamic observation. After 16 to 18weeks of gestation, fetal
gender can be identied (Figs.2.23 and 2.24).
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T. Yang et al.
Fig. 2.17 Fetal maxillofacial region. (a). Image of fetal orbits; (b). 2-D image of fetal mandible, mouth, and nostrils; (c). Image of fetal nose and
mouth; (d). Sagittal view of the fetal face; (e). Image of the fetal face; (f). Image of one fetal ear
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2 Application ofDiagnostic Ultrasound inthePerinatal Period
37
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Fig. 2.18 Fetal spine. (a, b). Full view of the fetal spine, vertebrae are arranged regularly, the spinal canal presents strip-like anechoic area, and
the spine has natural physiological curvature
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Fig. 2.19 Transverse view of fetal spine. (a, b). The vertebrae distribute as a triangle on transverse view of fetal spine
Fig. 2.20 Fetal ribs. (a). Transverse view of fetal ribs; (b). Sagittal view of fetal ribs
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T. Yang et al.
a
b
c
Fig. 2.21 Fetal thorax. (a). The Transverse view of the fetal thorax showing the heart; (b). Blood ow of fetal heart chambers; (c). The sagittal
view of the fetal thorax showing hyperechoic fetal lung, which can be clearly shown with a pleural effusion
Images ofFetal Limbs andFetal Movements
With the progress of the pregnancy, the echo of fetal bones is
gradually enhancing, accompanied by posterior attenuation.
Because of the amniotic uid surrounding the fetus, the
second trimester is the best period for observing fetal limbs
and their movements. During the third trimester, it is difcult
to display the fetal limbs due to the impact of fetal growth,
fetal position, amniotic uid, and other factors. After
28weeks of gestation, a small oval mass echo which is identied by visualizing the distal femur is the femoral epiphysis.
The appearance of skeletal epiphyseal ossication centers is
conductive to estimate gestational age (Figs.2.25 and 2.26).
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2 Application ofDiagnostic Ultrasound inthePerinatal Period
39
c
d
e
Fig. 2.22 Fetal abdominal cavity. (a). Homogeneous isoechoic fetal
liver locates in the right upper abdominal cavity; (b). A horn-shaped or
oval anechoic fetal stomach in the left upper abdomen; (c). Fetal intra-
hepatic arteries; (d). Hyperechoic bowels in the abdominal cavity; (e).
Fetal gallbladder
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T. Yang et al.
Fig. 2.23 Fetal kidney. (a). Transverse view of fetal abdomen showing the renal capsule, medulla, and pelvis; (b). Sagittal view of fetal abdomen
showing oval fetal kidney on the side of spine; and (c, d). Transverse and Sagittal images showing the blood ow of fetal kidney
Fig. 2.24 Fetal bladder and genitalia. (a, b). Sagittal and transverse
images of the lower abdomen show a circular anechoic bladder; (c).
Axial image of female genitalia in a fetus shows the labia majora on
both sides; (d). Image of male genitalia shows the scrotum, the penis,
and the testicles on both sides clearly
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Fig. 2.25 Fetal limbs. (a). Longitudinal view of fetal femur; (b). Sagittal view of fetal tibia and bula; (c). Sagittal view of fetal humerus; (d).
Sagittal view of fetal ulna, radius, and metacarpus
2.3.2.3 Fetal Appurtenances
Usually, the placenta is attached to anywhere of the uterine wall, including anterior, posterior, left lateral, right lat-
Placenta
The placenta is the organ that plays a crucial role in exchanging substances. As a combination of the embryonic and
maternal tissues, it is composed of the amnion, lobule chorion, and decidua basalis. The placenta at term is circular or
oval, 16 to 20cm in diameter, and 1 to 3cm in thickness
eral, or fundal. The placenta substance in the rst and second
trimesters shows uniform moderate echo. During the second
and third trimesters, the placenta can be divided into grades
0, I, II, and III according to the characteristics of the ultrasound image, which can be helpful to evaluate the maturity
of the placenta (Figs.2.29 and 2.30).
(generally no more than 5cm). The placenta is divided into
the fetal side and maternal side. The arteries and veins of the
umbilical cord radially distribute from the attachment of the
umbilical cord to the placental (Fig.2.27).
Fetal side of the placenta is covered with a smooth amniotic membrane, which presents as a thin strip-like hyperechoic. In contrast, the echo of the maternal side of the
placenta is close to that of the myometrium. And the
hypoechoic retroplacental space, composed of uterine vessels, can be visualized between posterior placenta and myometrium. The placental parenchyma appears as uniform and
intermediate echo (Fig.2.28).
Amniotic Fluid
Amniotic uid is an essential environment for fetal growth,
which protects the fetus and mother. The amount of amniotic
uid is sufcient in the second trimester and then decreased
gradually. The amount of amniotic uid signicantly reduced
in post-term pregnancy. The amniotic uid shows anechoic
areas for its excellent sound transmission. In the third trimester, moderate-echo particles are scattered in the amniotic
uid (Fig.2.31).
There are two methods to estimate the amniotic uid
with the use of ultrasound techniques: one is to measure