Sample Chapter Differential Diagnosis in Obstetric and Gynaecologic Ultrasound 3e by Bisset To Order Call Sms at +91 8527622422
P A R T
Early Pregnancy, 02
Fetal Well-Being and Growth, 24
Structural Fetal Abnormalities, 78
Fetal Face and Neck, 119
Fetal Thorax, 140
Fetal Echocardiography, 150
Fetal Abdomen and Pelvis, 169
Fetal Genitourinary System, 200
Fetal Musculoskeletal System, 220
C H A P T E R
MENSTRUAL AGE VERSUS
Menstrual age refers to the ﬁrst day of the last
normal menstrual period preceding pregnancy.
The menstrual age is used clinically for dating
pregnancy as it is an easily identiﬁable landmark.
Gestational age refers to age from conception and
usually lags behind the menstrual age by 2weeks.
THE FIRST TRIMESTER
The ﬁrst trimester is deﬁned as the 13weeks fol-
lowing the ﬁrst day of the last menstrual period.
The ﬁrst clue that the patient might be pregnant
is the appearance of a small cyst eccentrically
located within a single layer of the endome-
trium; this is soon followed by the appearance
of a double bleb sign, the yolk and then an echo-
genic cylinder that is the embryonic pole. There
is an echogenic rim around the early GS that is
the decidual reaction. The amniotic membrane is
seen to surround the early embryo; the YS is out-
side the amniotic cavity and is gradually pushed
to the periphery as the amniotic cavity expands.
These early ﬁndings are depicted in Figure 1-1.
ROLE OF ULTRASOUND IN THE
interstitial or ectopic
• To detect early pregnancy failure
1US should not be used solely as a diagnostic test to conﬁrm
the presence of uncomplicated pregnancy.
• To predict outcome in the presence of a live
• To assess gestational age, uncertain dates or
• To determine the number of embryos and assess
chorionicity and amnionicity
• To evaluate retained products of conception
• To diagnose gestational trophoblastic disease
• To diagnose some fetal anomalies
With TVS, there is improved detection rate of fetal
anomaly in the ﬁrst trimester. However, caution is
needed in interpreting certain ﬁndings in the ﬁrst
trimester such as cystic hygroma, choroid plexus
cysts, pyelactasis and echogenic bowel, which may
resolve spontaneously. A signiﬁcant false-negative
rate for fetal anomaly has also been recorded in
the ﬁrst trimester of pregnancy.
• To assess associated maternal abnormalities,
e.g. ovarian cysts, uterine leiomyomas and
• US-guided chorionic villus sampling
• To assess therapeutic abortion
PREDICTORS OF EARLY
Pregnancy failure in the ﬁrst trimester is a com-
mon problem, as approximately a quarter of
pregnancies fail during this period.
Lack of Cardiac Activity
Absent cardiac activity is taken to indicate death
but it should be remembered that in very small
FIGURE 1-1 Ultrasound features of early pregnancy. The earliest evidence of an IUP is the appearance of the GS, seen as a
small cyst in a single layer of the endometrium (A); soon a tiny two-compartment bleb appears inside (B); this is the double
bleb sign. Occasionally, a small amount of ﬂuid might be seen outside the GS; this early bleed might not be signiﬁcant but
does warrant a follow-up for conﬁrming viability (C). By about 5–6weeks, a small well-deﬁned internal cyst, the YS, and
a tiny bar of tissue, the embryonic pole, appear in the GS (D); at this time, embryonic cardiac ﬂicker might also become
apparent. An early sign of healthy pregnancy is the echogenic rim that is the decidualized endometrium (E); the absence of
this echogenic rim should raise concern of an abnormal pregnancy (F, a blighted ovum). The YS, vitelline duct and amni-
otic membranes become evident as well as a recognizable embryo with a large head and small limb buds (G, H); the YS is
outside the amniotic membrane and as the amniotic cavity forms and expands, this is pushed by the amnion against the
chorion; this is seen very well in image H. (Image H, courtesy of Dr Allen G. Worral, USA.)
CHAPTER 1 Early Pregnancy4
embryos (<4mm) cardiac ﬂicker might not be
appreciated and ultrasound should be repeated
after a few (2–3) days to conﬁrm this impression.
An embryonic length of 5mm is a threshold value
in ultrasound at which cardiac activity should be
visible in all cases (Figure 1-2J, O–Q).
Yolk Sac Characteristics
The YS functions as a haematopoietic organ and
facilitates nutrition transfer in early pregnancy
gestation. An abnormal Yolk Sac is associated
with embryonic death and poor pregnancy out-
come. Absence of a YS on TVS when GS size is
8mm or more is said to be 100% sensitive for
anembryonic gestation but has a 9% speciﬁcity
and a positive predictive value of 65%. Out of
these, 22% subsequently develop a viable preg-
nancy. However, the presence or absence of a
YS cannot be used to determine if a pregnancy is
normal when the GS is smaller than 18mm. Cal-
ciﬁcation is associated with a poor prognosis. An
abnormally shaped YS and lack of growth of the
YS are further signs of pregnancy failure. Unusu-
ally large or small YS (Figure 1-2C–F) has been
associated with embryonic death. Nevertheless,
transient abnormalities of YS shape may some-
times occur in normal pregnancies.
Gestational Sac Features
Just like embryonic length threshold values,
there are values for other structures that help
in deciding whether to wait or diagnose abnor-
mality. On TVS, an MSD of ≥18 mm should
always have a visible YS, and a mean sac diam-
eter of >20 mm should always have a visible
embryo. If the sac diameter has not reached
the threshold value, it would be prudent to
wait a few days; if the sac diameter exceeds
threshold values without the associated ﬁnd-
ings, an abnormal pregnancy can be diagnosed
(Figure 1-2A and B).
An irregular GS, thin or absent echogenic endo-
metrium (<2mm) around it (decidual reaction),
absent double decidual line sign are portends of
Small Sac Size: Discordance between
MSD and CRL
There is a large range of normal GS size. The
peak average difference between MSD and
CRL is 14.4mm at 8week menstrual age, which
progressively diminishes to less than 1mm by
12weeks menstrual age. Close follow-up is nec-
essary with borderline ﬁndings as patients can go
on to develop a normal pregnancy.
A collapsing amnion, an amnion with irregular
margins and an amnion with no visible embryo
indicate pregnancy failure. An enlarged amni-
otic cavity or a YS diameter more than 2
standard deviations above the mean when
compared with mean GS diameter is associ-
ated with poor outcome. A small amniotic cav-
ity with early oligohydramnios is a worrying
sign but should be diagnosed only when the
threshold of MSD-CRL <4 mm is crossed (Fig-
ure 1-2L and M).
FIRST TRIMESTER ANATOMY THAT
MAY MIMIC FETAL ANOMALY
The rhomboid fossa of the normally developing
rhombencephalon can appear as a small (3–4mm)
‘cystic’ structure in the posterior aspect of the
cranium, between 8 and 10weeks menstrual age
(Figure 1-3C). It should not be confused with
Dandy-Walker malformation, a cystic posterior
fossa abnormality. See image: Fig 3-15, page 112.
Telencephalic and Mesencephalic
The brain develops from the cranial part of the
neural tube. During the fourth week, the fore-
brain (prosencephalon), midbrain (mesencepha-
lon) and the hindbrain (rhombencephalon) form
as primary vesicles. During the ﬁfth week, the
forebrain divides into the telencephalon and
5CHAPTER 1 Early Pregnancy
FIGURE 1-2 Ultrasound features in early failed pregnancy. (A, B) A large GS (18–20m) without YS or embryonic pole
and a poor echogenic rim is a feature of early anembryonic pregnancy (blighted ovum). An abnormally large YS (>7mm)
is often associated with an abnormal outcome and in both cases (C, D) pregnancy failed to progress. Small echogenic YSs
(E, F, arrows) are also associated with poor outcome in many cases but a close follow-up in all cases of abnormal YS size
is recommended because a few can go on to normal pregnancy.
CHAPTER 1 Early Pregnancy6
FIGURE 1-2, cont’d Subchorionic haemorrhage, white arrow, (G–I) can range from an extensive collection almost all around
the GS (G) to a collection at one end (I); if the collection surrounds more than half the diameter of the sac or extends behind
the placental implantation site the prognosis is worse but follow-up should be done as the outcome is unpredictable and many
early pregnancies with early ominous looking collections go on to progress and many pregnancies with relatively trivial collec-
tions fail to thrive. Cardiac ﬂicker should be visible from very early on and in this 8 weeks pregnancy (J) with recent slight bleed-
ing it was not demonstrable; this is a black and white rendition of a Doppler image showing lack of cardiac activity and ﬂow.
This was a case of missed abortion. The patient in image (K) had a history of recent bleeding and on ultrasound a distorted
compressed GS was noted low down in the region of the body; this was an abortion in progress and the sac was expelled
within the next few hours, with no sac visible on a follow-up ultrasound after 24h.
7CHAPTER 1 Early Pregnancy
FIGURE 1-2, cont’d First trimester oligohydramnios, diagnosed when the sac is tight around the embryo has a generally
poor prognosis but caution must be used when diagnosing this. In some normal pregnancies (L) the MSD-CRL value falls below
10mm. The threshold for diagnosing ﬁrst trimester oligohydramnios is ≤4mm; image M shows a 12-week fetus with a large
abdominal cyst and complete anhydramnios with no measurable pocket amniotic ﬂuid seen. (N) Eight weeks missed abortion
with oligohydramnios. (O) Relatively normal looking embryo with absent cardiac activity; there is a large extra-amniotic space
(arrow). (P, Q) Distorted featureless embryo with absent cardiac activity and a large sac. (Image N, courtesy of Dr Jaydeep
Gandhi, India; image Q, courtesy of Dr Gunjan Puri, India.)
CHAPTER 1 Early Pregnancy8
diencephalon and the hindbrain divides partially
into the metencephalon and myelencephalon. The
telencephalic and mesencephalic vesicles appear
at about 7weeks gestation and can be detected
Physiologic Gut Herniation
This appears at about 8weeks and may persist
until 12weeks in 20% of normal fetuses. The
umbilical cord may be the site of cysts, varying
from 2 to 7mm, in under 1% of normal pregnan-
cies (Figure 1-3A).
TRANSIENT FIRST TRIMESTER
With TVS, there is improved detection rate of fetal
anomalies in the ﬁrst trimester. Caution is needed
in interpreting certain ﬁndings (vide infra).
Increased Nuchal Translucency
Increased ﬁrst trimester nuchal oedema/translu-
cency (NT) may be a transient phenomenon. How-
ever, persisting nuchal oedema may need close
follow-up as it is an important ultrasonographic
FIGURE 1-3 Normal ﬁrst trimester structures that can mimic fetal anomalies. (A) Physiological gut herniation (white
arrow); this is seen as an echogenic nodule projecting out of the abdominal wall, longitudinal section on the right and
transverse section on the left. (B) Limb buds (open arrows) that can appear as small echogenic nodules on the ventral
surface of the body. (C) Rhombencephalon appearing as a prominent cyst in the fetal brain (dashed arrow).
9CHAPTER 1 Early Pregnancy
marker of fetal chromosomal abnormality. NT in
the ﬁrst trimester is associated with aneuploidy
particularly trisomy 13, 18 and 21. An increased
NT at 11–14weeks gestational age is a common
ﬁnding in Down syndrome. NT is normally less
than 2.5mm; an increased measurement greater
than 2.5mm may indicate the presence of Down
syndrome or other chromosomal anomaly (Figure
1-4A–E). The presence of normal karyotype in the
presence of increased NT is a strong indication for
detailed ultrasound examination for nonkaryo-
type defects such as Noonan syndrome, Joubert
syndrome and congenital heart defects. The pres-
ence of an isolated increased NT is associated with
12.5% prevalence of chromosomal aberrations.
Very detailed protocols are available on how
to acquire accurate and reproducible NT mea-
surement (Box 1-1).
Nuchal Cystic Hygroma
One review of 72 fetuses with cystic hygroma diag-
nosed at 10–14weeks gestation found the mean
size of 7.9mm. Just over half had chromosomal
abnormalities of which the majority had Down
syndrome. The outcome of pregnancy is usually
unfavourable (miscarriage, elective termination,
and serious structural abnormalities). The overall
prognosis of fetal cystic hygroma (Figure 1-4F)
detected during the ﬁrst trimester is poor, and thus
sonographic evaluation of fetal nuchal translu-
cency thickness in the ﬁrst trimester is crucial.
Axillary Cystic Hygroma
Sonographic diagnosis of fetal axillary cystic
hygroma has been reported rarely, usually late in
gestation. Axillary hygromas are usually small,
transient, nonloculated cysts. Some are associ-
ated with chromosomal abnormalities. An asso-
ciation has been reported with trisomy 21 and
18. Early fetal axillary cystic hygromas are usu-
ally different from postnatal axillary cysts in
terms of prevalence, structure, and appearance.
It also may be a normal variant in the develop-
ment of the fetal lymphatic system.
Choroid Plexus Cysts
This is found in 3.6% normal fetuses; investiga-
tors are divided on the question of amniocentesis
in isolated CPC but most agree that the presence
of additional US abnormalities is an indication
for amniocentesis. Abnormal karyotype is found
in 1–2.4% of fetuses with isolated CPC.
Isolated mild pyelactasis (<3/4mm) without
progressive change is not associated with sig-
niﬁcant pathology and is found in 3.2% of
fetuses. Mild pyelactasis is characterized by a
small amount of ﬂuid in the renal pelvis and is
affected by maternal hydration. However, mild
pyelactasis may be a sign of early pathological
state. The appropriate threshold for initiating
further investigation particularly in the ﬁrst
trimester is controversial but a close watch is
Generally when a fetal pericardial effusion is
observed it is along one portion of the ventricle
or near an atrioventricular valve, but does not
surround the heart. A pericardial effusion sur-
rounding the heart is considered abnormal even
Pleural effusion is considered abnormal at any
gestational age and even when transient the fetus
needs to be evaluated for chromosomal abnor-
mality, Turner syndrome, immune hydrops feta-
lis, cardiac abnormalities, diaphragmatic hernia,
lymphangiectasia and intrauterine infections.
Sonographic appearances are those of anechoic
ﬂuid collection that conform to fetal chest associ-
ated with ﬂattening/inversion of the diaphragm
and bulging of the thoracic wall. Chylous effu-
sions are indistinguishable from serous pleural
effusion in the fetus.
CHAPTER 1 Early Pregnancy10
FIGURE 1-4 Nuchal translucency; normal measurement (A, B), increased NT (C, D), markedly increased (E); in this patient,
the oedema is generalized and is all around the body (space suit appearance). There is posterior cystic hygroma forma-
tion in (F); this has a very high association with aneuploidy, especially Turner syndrome. (Images B, D, and E, courtesy of
Dr Allan J. Worral, USA; image F, courtesy of Dr Latha Nataranjan, India.)
11CHAPTER 1 Early Pregnancy
Fetal echogenic bowel should be investigated and
followed up carefully as it is considered as one
of the soft markers for aneuploidy, IUGR, infec-
tions and cystic ﬁbrosis.
INTRAUTERINE FLUID COLLECTIONS
THAT MAY MIMIC A GS
A variety of conditions causing ﬂuid collections
within the uterine cavity may, in the appropri-
ate clinical setting, mimic a GS. Intrauterine ﬂuid
collections lack the double ring margin of an IUP
and in many of the causes listed below will lack
a trophoblastic reaction.
• Endometrial bleeding
• Retained products of conception
• Incomplete abortion
• Pseudogestational sac of EP
• Endometrial carcinoma
• Cervical stenosis/cervical obstruction due to a
carcinoma or previous surgery
• Endometrial arterial aneurysm – this life-
threatening condition has been reported only
once; on close inspection it was found to be
pulsatile on US, while a duplex arterial wave-
form was detected.
A GS is classiﬁed as empty when no fetal parts
are identiﬁed on abdominal scanning in a sac
that exceeds 30mm in diameter or with no YS
in a sac that exceeds 20mm in diameter. Most
• The gestational period must be 11–13weeks and 6days.
• The fetal CRL should be between 45 and 84mm.
• The magniﬁcation of the image should be such that the
fetal head and thorax occupy the whole screen.
• A mid-sagittal view of the face should be obtained.This is
deﬁned by the presence of the echogenic tip of the nose
and rectangular shape of the palate anteriorly, the translu-
cent diencephalon in the centre and the nuchal membrane
posteriorly. Minor deviations from the exact midline plane
would cause nonvisualization of the tip of the nose and
visibility of the zygomatic process of the maxilla.
• The fetus should be in a neutral position, with the head
in line with the spine. When the fetal neck is hyperex-
tended the measurement can be falsely increased and
when the neck is ﬂexed, the measurement can be falsely
• Care must be taken to distinguish between fetal skin and
• The widest part of the translucency must always be
• Measurements should be taken with the inner border of
the horizontal line of the callipers placed on the line that
deﬁnes the nuchal translucency thickness – the crossbar
of the calliper should be such that it is hardly visible as
it merges with the white line of the border, not in the
• In magnifying the image (pre- or postfreeze zoom), it is
important to turn the gain down.This avoids the mistake
of placing the calliper on the fuzzy edge of the line which
causes an underestimate of the nuchal measurement.
• During the scan more than one measurement must be
taken and the maximum one that meets all the above
criteria should be recorded in the database.
• A new approach for the measurement of NT which
improves the accuracy of measurements, is with the use
of a semiautomated technique. The operator places a
box in the nuchal area and the machine automatically
selects the best measurement, which uses an algorithm
that draws a line through the centre of the nuchal mem-
brane and another line at the edge of the soft tissue
overlying the cervical spine. The measurement obtained
by this method is similar to that obtained manually and
it is therefore applicable to the software of the Fetal
• The umbilical cord may be round the fetal neck in about
5% of cases and this ﬁnding may produce a falsely
increased NT. In such cases, the measurements of NT
above and below the cord are different and, in the calcu-
lation of risk, it is more appropriate to use the average of
the two measurements.
BOX 1-1 Protocol for Measurement of Nuchal Translucency
Reproduced with permission from Fetal Medicine Foundation.Available at www.fetalmedicine.com.
CHAPTER 1 Early Pregnancy12
empty sacs are abnormal in shape (Figures 1-1F
and 1-2A and B).
This is less likely with TVS
as GS is seen as early as
32days and is seen in all
pregnancies with hCG
levels of 1000mIU/mL
Blighted ovum This term applies to
arrested development of
a fertilized ovum. Most
blighted ova are of an
sac of EP
The double decidual sign is
absent in a pseudogesta-
POSITIVE βhCG WITHOUT IUP
Human chorionic gonadotropin (hCG) is a glyco-
protein hormone produced by trophoblastic tissues.
As trophoblastic tissue is an essential part of preg-
nancy; identiﬁcation of hCG is frequently sought
to conﬁrm the presence of pregnancy. However, a
false-positive hCG assay may arise in conditions
other than pregnancy as hCG may be elaborated
by the pituitary, exogenous sources, and both tro-
phoblastic and nontrophoblastic neoplasia, result-
ing in false-positive laboratory assays for hCG.
• Early IUP <5weeks gestation
• Recent complete or incomplete abortion
• βhCG-producing ovarian tumour – germ cell
tumour, primary ovarian choriocarcinoma
• Theca lutein cyst associated with pharmaco-
logical stimulation with βhCG
• Exogenous administration of hCG: hCG is
used by some as an aid in weight loss by intra-
muscular or oral administration. Following
cessation of hCG therapy for 24h the hCG
assay usually turns negative on a repeat assay.
• Pituitary hCG: Stimulated by gonadotropin-
releasing hormone; suppressed by gonadotro-
pin-releasing hormone agonist and oestrogen/
progestin therapy. Can also be detected in
postmenopausal women due to increased
• Trophoblastic neoplasm: Consists of pregnancy,
gestational trophoblastic neoplasia, and pla-
cental site trophoblastic tumours.
OF EARLY IUP
A GS is surrounded by an echogenic asymmet-
rical ring that should be visible at 5weeksMA
on transabdominal US scan, while on TVS a GS
is seen at 32days. A normal sac growth is 0.7–
1.75mm/day (mean=1.33) from 5 to 11weeks.
In patients with early pregnancy with a question-
able GS a 10MHz intravaginal probe improves
the diagnostic conﬁdence.
Double Decidual Sac
A DDS is useful at 4–6weeks gestational age;
it consists of two concentric rings of tissue sur-
rounding a portion of an intrauterine GS. The
sign develops as a result of protrusion of the GS
into the uterus.
At 6weeksMA, a YS and amnion should be visible
on transabdominal US. On TVS, a YS is seen in
every pregnancy between 36 and 40days; the GS is
between 6 and 9mm. YS is seen in 100% normal
pregnancies with βhCG level of 7200mIU/mL.
This is when the GS is not sufﬁciently large to
impress, protrude into or deform the uterine cen-
tral echo complex yet is completely embedded
within the decidua. This sign precedes the double
decidual sign. This sign does not appear to be
sensitive or speciﬁc in the diagnosis of IUP.
Embryo with Heartbeat
Embryo with a heartbeat is expected in all preg-
nancies >40days and a GS >9mm on TVS.
13CHAPTER 1 Early Pregnancy
RISK GROUPS FOR EP
EP rates have increased steadily from 4.5 per
1000 pregnancies in 1970 to 16.8 per 1000 preg-
nancies in 1987. All women of reproductive age
are at risk of EP.
Higher Risk Groups: EP
• Delayed transit of zygote
ø Previous tubal pregnancy (10-fold increase)
ø Previous tubal surgery
ø Previous salpingitis particularly chlamydia
ø Infertility – shared tubal abnormalities with
ø Ovulation induction
ø In vitro Fertilization multiple pregnancy
ø Gamete intrafollicular transfer – contributory
factors include the hydrostatic forces gener-
ated during transfer
ø Intrauterine contraceptive devices
ø History of PID
ø Increasing maternal age and parity
ULTRASOUND FINDINGS IN EP
EP is not always easy to diagnose; the classic triad
of missed period, pain and abnormal vaginal
bleeding is frequently absent and adnexal mass
or cervical tenderness cannot be demonstrated in
Correlation with ultrasound and serum βhCG
help in making the correct diagnosis in many
Ultrasound is fairly conclusive in the follow-
• The demonstration of a live pregnancy out-
side the uterus. With cardiac ﬂicker and/or the
conclusive demonstration of a YS.
• The demonstration of a thick ring-like struc-
ture with an echogenic rim and an extra-
ovarian location is fairly speciﬁc. Beware
of the corpus luteum that can mimic an
ectopic, but the corpus luteum is ovarian
in location while an EP is almost always
• The demonstration of a live IUP excludes most
cases of ectopic pregnancy, although a con-
current ectopic and IUP can still be possible
(heterotopic pregnancy); this situation is more
likely to be met in patients undergoing infertil-
The presence of a complex adnexal mass, absent
IUP and rising serum βhCG levels make the diag-
nosis of EP likely.
Free peritoneal ﬂuid, especially if complex and
associated with an adnexal nonovarian mass,
increases the likelihood of an EP. The likelihood
increases if the amount of ﬂuid is large (reaches
US is more sensitive than culdocentesis in
detecting haemoperitoneum. The presence of
echogenic ﬂuid, which correlates with haemo-
peritoneum, is highly suggestive of EP espe-
cially when a large quantity of echogenic ﬂuid is
detected in the presence of an adnexal mass.
This refers to the collection of a small amount of
ﬂuid within the decidualized endometrial canal.
This is differentiated from a true GS by its cen-
tral location (true sac is in one layer of the endo-
metrium) and fusiform or tear drop shape with
an inferiorly pointing beak (true sac is usually
rounded). A pseudosac will not show a double-
line sign, YS or an embryonic pole.
This refers to a thick-walled cystic structure
in the adnexa quite separate from the uterus
and ovary and is considered a reliable sign of
EP. The tubal ring can mimic a corpus luteum
cyst when the ovary is not well seen. A corpus
luteum cyst is usually thinner, contains clear
ﬂuid and appears less echogenic than the endo-
metrium. Confusion with a haemorrhagic ovar-
ian cyst may arise when surrounding ﬂuid is
CHAPTER 1 Early Pregnancy14
An empty uterus in an at-risk woman in associa-
tion with a hCG greater than 1800IU/L is highly
suggestive of the presence of EP. This level of
hCG is highly suggestive of EP but is not diag-
nostic. It is reasonable to closely follow up rather
than treat early stable cases of EP.
Other Biochemical Aids to US
Progesterone is produced by the corpus luteum
during the early second trimester, until the placenta
takes over production of progesterone. A serum
progesterone of <5ng/mL is 99.8% predictive of
a nonviable pregnancy either EP or IUP. Progester-
one levels measuring at least 25ng/mL excludes
97.5% of EPs.
The levels of progesterone are independent of
gestational age so that a single test can be diag-
nostic without the need for serial examinations.
Endometrial Thickness 0.5–1.7cm
Endometrial changes in the form of a decidual
cast occur in 50% of patients and may be indis-
tinguishable from IUP. There is no signiﬁcant dif-
ference in endometrial thickness between women
with EP and those with spontaneous abortion.
A thin endometrium seen on TVS cannot be used
to exclude the diagnosis of EP.
Doppler Sonography in EP
High-velocity and low-impedance ﬂow is seen in
both IUP and EP. Colour Doppler often shows
a complete or partial ‘ring of ﬁre’ sign in an
adnexal mass; this has a low-resistance, high-
diastolic component on spectral Doppler. Cor-
pus luteum has similar ﬂow characteristics but
this is intraovarian in location while an ectopic is
almost always extraovarian.
Spontaneous Resolution of EP
In some patients, an EP resolves spontaneously
but the exact incidence is unknown.
The features of EP are depicted in Figure 1-5.
Endometrial Three-Layer Pattern
A well-deﬁned spherical structure forming three
hyperechoic layers separated by two hypoechoic
layers within the endometrium have been
described with EP. However, this sign is con-
troversial and has been described in a variety
of conditions besides being a normal appear-
ance too. The differential diagnosis of the sign
includes early IUP and successful implantation in
women undergoing in vitro fertilization. It has
also been described with trophoblastic regres-
sion: symptomatic pregnant patients, clinically
stable, serum levels of βhCG levels below a dis-
criminatory zone, who lack US evidence of either
EP or IUP and when symptoms and serological
evidence of pregnancy resolve spontaneously.
DIFFERENTIAL DIAGNOSIS OF EP
• Any adnexal mass
• All causes of ﬂuid in the cul-de-sac
• Corpus luteum cysts with/without septa
• Torsion of ovarian cyst/neoplasm
• Tubo-ovarian abscess
• Torsion/degeneration of a ﬁbroid
• Ovarian neoplasm
• Haemorrhagic ovarian cyst
• Uterine leiomyoma
• Haemorrhagic subserosal ﬁbroid
• Appendix abscess
• Diverticular abscess
FOR MEASUREMENT OF
Approximate Age (Weeks)
5–6 GS volume
12–15 BPD, FL, head circumference
24 After 24weeks, there is variation in
the rate of growth depending upon
genetic and environmental factors
and ultrasound dating becomes
progressively less accurate
15CHAPTER 1 Early Pregnancy
FIGURE 1-5 Spectrum of ultrasound ﬁndings in EP. The most suggestive ﬁnding is of a thick-walled echogenic ring-like
structure that is extraovarian (A, B). On Doppler, there is often a hypervascular area surrounding this, the ‘ring of ﬁre’ sign
(C); a YS and an embryo can sometimes be recognizable conﬁrming the diagnosis (D) and a cardiac ﬂicker can be picked
up (E). Beware of a small collection in the endometrial canal that can mimic an intrauterine GS (F); in fact, this is called
the pseudosac of EP. The ectopic can lead to bleeding into the peritoneum and a complex ascites ensues, and echogenic
specks, septations and clumps in the ascetic ﬂuid can form (G, H). The white arrow in all images points to the ring-like
structure representing the ectopic GS.
CHAPTER 1 Early Pregnancy16
GS can be visualized from 4weeks on TVS and
a week later on transabdominal scans. The sac is
rarely spherical, so a single diameter is likely to
be inaccurate and the average of the three diam-
eters (AP, transverse and craniocaudal) is used.
The inner-to-inner border is used to read off the
sac size against standard charts.
This is the most accurate means of dating a preg-
nancy. Fetal attitude, especially considerable ﬂex-
ion can reduce the reading and the examiner should
wait for a more neutral fetal spine curvature before
making the measurement. CRL is not affected by
most environmental and racial factors.
This is generally used in the second and third trimes-
ters; the accuracy decreases as pregnancy advances.
The FL may be measured from 12weeks onwards.
It compliments BPD measurement and should be
used in all cases. In fact, any long bone can be
measured but the FL is easiest to identify and
measure, making it the most popular long bone.
OTHER FETAL MEASUREMENTS
This is a bit more difﬁcult to measure than the
BPD or FL but is useful in assessing the weight
of the baby, growth appropriateness or dispar-
ity between fetal parameters, IUGR, over growth
This is a very useful measurement especially when
the fetal head shape exhibits undue narrowing
(dolichocephaly) or undue broadening; both
conditions are normal variants but can lead to a
misleadingly small or large BPD.
Analysis of fetal weight may be performed using
standard fetal measurements (AC, HC, FL, BPD,
etc.), either singly or in combination. Adding
parameters increases accuracy slightly but fetal
weight measurement tends to be accurate only
within ±10% at best.
Fetal Foot Length
There are limitations to the use of fetal foot
length for gestation age assessment particularly
in fetuses with growth abnormalities.
The Transverse Cerebellar Diameter
The transverse cerebellar diameter (TCD) is con-
sidered as a reliable parameter for estimating the
duration of gestation. In IUGR, restriction of the
cerebellum is usually spared, making TCD a reli-
able indicator of gestational age even when other
parameters fall off the appropriate growth curve.
Throughout pregnancy, TCD measurements
allow for the estimation of gestational age that
is independent of the shape of the fetal head and
offers potential for evaluation of abnormal fetal
growth and anomalous development of the central
CAUSES OF INACCURACY IN
ESTIMATING GESTATIONAL AGE
FROM MENSTRUAL HISTORY
• LMP date not accurately known
• Cycle is irregular
• Cycle is not 28days long
• Bleeding in early pregnancy may mimic a men-
• Contraceptive pill recently used as a form of
• Postdelivery breast feeding
17CHAPTER 1 Early Pregnancy
ADVANTAGES OF ULTRASOUND
ESTIMATION OF GESTATIONAL AGE
• Allows planning for delivery, including deci-
sions for induction of labour and efforts at
prolonging pregnancy in cases where the appro-
priate period has been exceeded or not reached.
• Is vital for the correct interpretation of screen-
ing blood tests such as the triple or quad screen
for Down syndrome and other conditions.
• Is imperative for diagnosing fetal growth
CORPUS LUTEUM IN EARLY
The corpus luteum (CL) is identiﬁed in the ﬁrst tri-
mester on TVS in most pregnancies. This physiolog-
ical structure produces progesterone, which sustains
pregnancy until the placenta is formed. At around
7weeks gestation, the functioning CL is no longer
necessary because the placenta assumes hormonal
function. Consequently, it decreases in size during
8–16weeks gestation and is subsequently main-
tained passively for the rest of the term of pregnancy:
• Varied US appearances with a mean diameter
of 1.9±0.6cm (range 0.8–5.5cm)
• Hypoechoic – 34%
• Cystic with thick circumferential wall and
anechoic centre – 27%
• Thin-walled simple cyst – 15%
• No CL identiﬁed – 2%
• Circumferential ﬂow partial or all CL on
colour ﬂow Doppler – 92%
• Flow on pulsed Doppler in 92% with a mean
resistive index of 0.49±0.08 (range 0.29–0.91)
THE CERVIX IN PREGNANCY
Normal Cervix in Pregnancy
It is usually difﬁcult to distinguish the cervix
from the lower uterine segment in the nongravid
state and the ﬁrst trimester. From midtrimes-
ter onwards, the amniotic sac clearly deﬁnes
the internal os. US has advantages over digital
examination; the internal os can be visualized
by sonography and hence early changes of cer-
vical incompetence can be detected; moreover,
there is a decreased risk of infection and cervical
Cervical length is the distance between the
internal and external os. The ﬁrst trimester
cervical length is >5 cm. The cervical length
decreases to <34 mm at 28 weeks gestation. In
patients with multiple gestation, there is sig-
niﬁcantly shorter cervical length. Normograms
have been developed for twins and triplets that
help to identify patients at high risk for pre-
There is an inverse relationship between US
cervical length and the risk of preterm labour.
Length <25mm at 24weeks' gestation indicates
a fourfold increased risk of preterm labour. Fun-
nelling/wedging of the internal os with prolapse
of fetal membrane is indicative of the onset of
preterm labour. Funnelling of over 60% of the
length of the cervical canal is also associated with
Cervical incompetence is deﬁned as cervi-
cal dilatation without uterine contractions. In
patients with a history of pregnancy loss, it is
prudent to establish a baseline cervical length
measurement before the gestation age when
the previous loss occurred with follow-up
scans 1–2 weeks depending upon the ﬁndings
or recent examination or symptoms. TVS com-
bined with transfundal pressure or scanning
patient in a standing position can illicit early
CHAPTER 1 Early Pregnancy18
Dynamic Changing Cervix
This dramatic event can be seen during US exam-
ination. The cervix shows dynamic changes with
varying degree of funnelling of the internal os
associated with vigorous closing and opening of
the cervix. These changes occur in the absence
of uterine contractions. Although most patients
with a spontaneously changing cervix deliver
preterm, it is not a sign of imminent delivery and
with conservative management delivery may be
delayed in some.
Sonographic guidance can be used to assist place-
ment of cervical cerclage as a prophylaxis to pre-
term labour in cervical incompetence. Following
placement of cervical cerclage, measurements of
the canal are made from the internal os to the
level of cerclage. Shortening of the upper cervical
length <1cm is associated with preterm delivery.
The Cervix at Term
Several studies using US to evaluate the ripeness
and inducibility of cervix have been published
and a scoring system has been proposed. Param-
eters such as cervical length, cervical diameter
and the appearance of the internal os are scored.
Using these indices it has been shown that the
presence of funnelling and a short cervical length
is associated with a shorter duration of induced
labour. US has been shown to correlate well
with digital examination; however, the ﬁrmness
of the cervix, which is an important sign of the
ripeness of the cervix can only be assessed digi-
tally. US technique is useful in patients in whom
digital examination is contraindicated such as in
patients with premature rupture of membranes
and unexplained vaginal bleeding.
FALSE-POSITIVE FINDINGS OF
• Uterine contraction – differentiation by the
observation of a thickened myometrium
associated with uterine contractions, palpa-
tion of the uterus, placement of tocodyna-
mometer and questioning the patient may
disclose the presence of uterine contractions
• Narrowed lower uterine segment can mimic
funnelling – clariﬁed by observing the cervix
• Overdistended urinary bladder impression on
the lower uterine segment may produce the
impression of funnelling of the cervix
• Cystic lesions such as nabothian cysts and
vaginal cyst can mimic a dilated internal os
INCOMPETENT CERVIX: RISK
• DES exposure in utero associated with cervical
• Previous cone biopsy of the cervix
• Prior cervical laceration
• Prior cervical trauma – cauterization, dilatation,
• Ostrogen therapy
There is 10–25% pregnancy loss rate of all clini-
cally diagnosed pregnancies. The majority of the
losses occur before the seventh week of gestation
usually due to abnormal karyotype of which 52%
are trisomies, 20% triploidy and 15% monosomy.
There is complete loss of products of conception
with a closed cervix and a thin endometrium on US.
Incomplete Spontaneous Abortion
There are retained products of conception with
continued bleeding associated with a patulous
cervix. The retained products may represent pla-
cental tissue or fetal tissue. US ﬁndings include
GS/ﬂuid collection, GS with a dead fetus, endo-
metrial thickness >5mm in the majority but
thickness may vary from 2 to 5mm; in 14%,
thickness may be 2mm or less. Complications
19CHAPTER 1 Early Pregnancy
include endometritis, septicaemia, and diffuse
The GS becomes detached from its implantation
site within the uterus so that abortion becomes
inevitable and usually occurs within a few hours.
Presentation is usually with PV bleeding <7days,
persistent painful uterine contractions, a dilated
cervix and ruptured membranes. US ﬁndings
include a GS low within the uterus, GS surrounded
by an anechoic zone of blood and a dilated cervix.
This usually occurs between 8 and 14weeks gesta-
tion. There is a dead conceptus within the uterus
usually associated with a brownish vaginal dis-
charge with a closed cervix. US features include
no cardiac activity in the embryo of appropriate
size, gestation inappropriate for menstrual age,
GS >25mm with no embryo, GS >20mm with-
out a YS, misshapen GS, debris within the GS,
lack of a double decidual sac, a low sac position
(Figure 1-2K) and a subchorionic ﬂuid collection
This is ﬁrst trimester PV bleeding associated with
a live fetus and closed cervix. The incidence is
20–25% of all clinically apparent pregnancies
with a 50% pregnancy loss rate. Fetal viability
depends on the detection of fetal heartbeat and
movement. Early fetal bradycardia, relative fetal
inactivity and the presence of a large subchori-
onic haematoma are poor prognostic signs.
FETAL ANOMALIES DETECTABLE
ON ULTRASOUND IN THE FIRST
Head and Neck
• Cystic hygroma
• Nuchal translucency
• Large cranial cysts
• Choroid plexus cysts
• Dandy–Walker malformation
• Neural tube defects
• Ectopia cordis
• Lateral fold defect
• Short limb dysplasia
• Atrioventricular canal defect
• Complete heart block
• Megacystis (Figure 1-2M)
• Cystic dysplastic kidneys
Placenta, Umbilical Cord and YS
• Partial mole
• Umbilical cord cysts
• Short cord associated with ventral fold defect
• Large YS
• Monoamniotic twins
• Twin–twin transfusion syndrome
• Conjoined twins
CHAPTER 1 Early Pregnancy20
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