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Chapter 41 ■ Fetal Hydrops 1427
A B
FIGURE 41-4. Hydrocele. A, Ultrasound, and B, MRI, appearances of male fetus with hydrops with fluid extending into the scrotum.
A
FIGURE 41-5. Massive ascites leading to lung com-
pression. Coronal T2-weighted MR image shows massive
ascites (A) surrounding the liver (L) and bowel (B). Note the
compression of the fetal lungs (arrows).
L
B
mediastinal shift, obstructing venous return and leading
to hydrops. In large, bilateral pleural effusions the lungs
appear as free-floating “bat wings” beside the heart
(Fig. 41-6, D). When chronic, large effusions can lead
to pulmonary hypoplasia. As pleural effusions enlarge,
compression or kinking of mediastinal vascular structures causes upper body edema and functional esophageal obstruction, leading to secondary polyhydramnios.
Chylothorax is the most common cause of pleural
effusion leading to respiratory distress in the newborn.
This is an important diagnosis to suggest when associated with hydrops because drainage can be curative.
Drainage of the effusion can lead to reversal of hydrops
and can prevent pulmonary hypoplasia. Drainage immediately before delivery can assist in peripartum care.
When drained, the fluid has a large number of lymphocytes in clear, yellow fluid. The fluid will not be “milky”
until after the infant feeds.
Pericardial Effusions
In contrast to pleural effusions that surround the lungs
and compress the tissue medially, pericardial effusions
are anteromedial fluid collections. Fluid collections of up
to 2 mm in thickness are common, and a small amount
of pericardial fluid (up to 7 mm, in isolation) can be a
normal finding8 (Fig. 41-8; Video 41-3). A large pericardial effusion compresses the lungs against the posterior chest wall (Fig. 41-9). The heart is visualized as
“floating” within the anterior thoracic fluid collection.
Subcutaneous Edema
Subcutaneous edema may be localized or generalized,
depending on the etiology. A thickness of 5 mm has
been suggested as the cutoff value.9 Edema is most easily
seen over the fetal scalp or face, where thickening of skin
overlying bone is visualized (Fig. 41-10, A). It is important to realize that the biparietal diameter and head
1428 PART IV ■ Obstetric Sonography
R
L
A B C
D E F
FIGURE 41-6. Fetal pleural effusions. A, Unilateral small right pleural effusions. B, Moderate right (R) and small left (L) effu-
sions. C, Moderate right effusion. Note moderate mediastinal shift to the left. D, Bilateral moderate effusions. Note how the partially
compressed lungs appear as free-floating “bat wings.” E, Axial, and F, oblique, coronal views of large right pleural effusion. Note the severe
mediastinal shift in E.
FIGURE 41-7. Small pleural effusion in association with congenital cystic adenomatoid malformation.
Note the large cystic mass (calipers) and small pleural effusion (arrow).
Chapter 41 ■ Fetal Hydrops 1429
A B
FIGURE 41-8. Normal finding of small amount of pericardial fluid. A and B, Note the small rim of anechoic fluid
(arrows) in two different fetuses.
FIGURE 41-9. Large pericardial effusion. Lungs are
compressed posteriorly.
circumference measurements are taken around the skull
bone, excluding the skin. Subcutaneous edema may
also be seen over the limbs and abdominal wall. Care
should be taken not to mistake prominent fat in
a macrosomic fetus to anasarca in a hydropic fetus.
Subcutaneous edema will increase the abdominal circumference measurement, beyond that which is expected
for gestational age (Fig. 41-10, B). It is important when
measuring the fetus to include the entirety of the skin in
the abdominal circumference measurement, because this
affects the weight calculation of the fetus. Thus, when
performing biometric assessment of the hydropic fetus,
the abdominal circumference measurement is included
in the weight calculation, but it should be excluded
from the gestational age assessment so that the thickened
skin does not falsely elevate fetal age. When generalized
subcutaneous edema is present, the appearances may
be referred to as anasarca (Fig. 41-11, Video 41-4).
Note that on fetal magnetic resonance imaging (MRI),
body wall edema will appear of high signal intensity
on T2-weighted images, similar to surrounding fluid
(Fig. 41-12).
Placentomegaly
Placental edema is a variable and usually late sign in
hydrops (Fig. 41-13). The sonographic texture of the
placenta may be altered, and its appearance may be
described as thickened, echogenic, spongy, or ground
glass. Placental dimensions, especially thickness, are
increased above the normal of 5 cm in the third trimes-
9-11
When placental edema is secondary to an hydropic
ter.
process in the fetus, the entire placenta is usually affected.
This finding may be used to exclude the very rare primary
placental causes of hydrops (e.g., chorioangioma).
Polyhydramnios
The assessment of amniotic fluid is described in Chapter
46. Polyhydramnios occurs frequently in conjunction
with hydrops (Fig. 41-14; see Video 41-1). This increases
the risk of prematurity, which adds to the morbidity
associated with hydrops.
1430 PART IV ■ Obstetric Sonography
A B
FIGURE 41-10. Scalp and body wall edema are measured differently. A, Fetal scalp edema. Head measurements
(cursors) are obtained around the bone, not the skin; BPD, biparietal diameter; HC, head circumference. B, Abdominal wall thickening.
Abdominal wall measurements are obtained around the abdomen, including the skin thickening; AC, abdominal circumference. Note that
gestational age is 27 weeks by HC, but 34 weeks if only AC is used.
A B C
D E F
FIGURE 41-11. Anasarca in fetus with Turner’s syndrome. A, Axial view of cystic hygroma behind the neck. B, Coronal
view of diffuse scalp edema and cystic hygroma. C, Axial view of thoracic wall edema. D and E, Axial views of abdomen show body wall
edema and ascites. F, Arm with anasarca as well.
ETIOLOGY
and size of fluid collections and edema as detected by
ultrasound may provide a clue to the etiology of hydrops.
Before the availability of Rh0(D) immune globulin
(RhoGAM), immune hydrops represented greater than
80% of all cases of hydrops. Now, nonimmune hydrops
represents 90% of cases. The distribution, timing,
For example, in immune hydrops, ascites appears first,
with subcutaneous edema appearing only with more
advanced anemia. Intrathoracic collections generally do
not occur or occur late in the process.
Chapter 41 ■ Fetal Hydrops 1431
A B
FIGURE 41-12. Fetal body wall edema on MRI. A and B, Axial and sagittal T2-weighted MR images show how edema appears
as high signal in the skin.
FIGURE 41-13. Placental edema. Placental thickness is
normally about 1 mm of thickness per week gestational age, and
it should not exceed 5 cm in the third trimester.
Generally, pleural and pericardial effusions appear
earlier and more prominently with thoracic pathologies,
whereas ascites appears earlier and predominates with
anemia and primary abdominal pathologies. Massive
ascites with associated bowel hyperechogenicity is typical
of either parvovirus infection (when the ascites is very
tense) or a bowel perforation that may be secondary to
meconium peritonitis (Fig. 41-15). Localized fluid col-
lections may progress to hydrops because of pressure or
metabolic effects, and thus the pattern of hydrops may
evolve over time.
FIGURE 41-14. Polyhydramnios. A 12-cm pocket of fluid
(cursors) in pregnancy with hydrops.
IMMUNE HYDROPS
Immune hydrops, or erythroblastosis fetalis, occurs
when a sensitized mother develops antibodies to fetal
RBCs that lead to hemolysis. Circulating maternal
immunoglobulin G (IgG) antibodies cross the placenta
and attack antigen-positive fetal RBCs. The majority
of cases still occur in the presence of Rh(D) antibodies. Atypical antibodies such as Kell, Rh(C), and
Rh(E) develop in 1% to 2% of individuals after blood
1432 PART IV ■ Obstetric Sonography
A
FIGURE 41-15. Meconium peritonitis. A, Matted and dilated echogenic bowel with ascites, typical of meconium peritonitis.
B, Tense ascites in meconium peritonitis.
A
FIGURE 41-16. Immune hydrops. A, Ascites (arrow). B, Middle cerebral artery measuring peak systolic velocity (PSV); EDV, end
diastolic velocity; RI, resistive index.
B
B
transfusion and cause 2% of hemolytic disease of the
fetus. The result is anemia, extramedullary erythropoiesis, hepatosplenomegaly, hypoalbuminemia, and congestive heart failure (CHF). Hydrops develops when the
fetal hemoglobin (HbF) deficit
exceeds 7 g/dL,12 probably because of reduced oncotic pressure secondary to
hypoalbuminemia, combined with high-output cardiac
failure (Fig. 41-16). Eventually, the fetus develops both
metabolic and lactic acidosis,
13,14
and once this decompensation occurs, progression of hydrops is rapid, leading
to fetal demise within 24 to 48 hours.
Causes of maternal sensitivity include fetal maternal
hemorrhage and transplacental hemorrhage. In women
with incompatible blood types with respect to the fetus
(Rh alloimmunization, other RBC antigen), antibodies
can be made. This typically occurs after delivery of the
first pregnancy and therefore will affect the second pregnancy. Other times of blood sharing include abortion
(spontaneous or therapeutic), amniocentesis, placental
abruption, incompatible blood transfusions, and transplacental hemorrhage. An additional blood incompatibility issue is fetal alloimmune thrombocytopenia.
To avoid maternal sensitization, 300 mg of RhoGAM
is given at 28 weeks’ gestation in sensitized individuals.
This protects against 30 mL of fetal blood. If a greater
degree of fetomaternal hemorrhage is suspected, a Kleihauer-Betke test can be done to quantify fetal blood
in maternal circulation to determine the necessary dose.
As a prophylactic measure, RhoGAM is given to Rhnegative women within 48 hours after invasive fetal
procedures such as amniocentesis and chorionic villus
sampling.
Chapter 41 ■ Fetal Hydrops 1433
Management of the Fetus
Immune hydrops is an indication for urgent fetal blood
sampling and transfusion. This technique is performed
by percutaneous ultrasound-guided blood sampling
(PUBS)
15
(see Chapter 46). In a study of 80 fetuses with
hydrops secondary to anemia, when hydrops was mild
before treatment (only a thin rim of ascites, with or
without pericardial effusion), hydrops was reversed in
88%; when hydrops was severe before treatment, hydrops
reversed in only 65%. This stresses the importance of
early treatment in cases of suspected anemia. After reversal of hydrops, survival rate was 98%.
loss rate after this procedure is about 1.4%.
16
The incremental
17
Noninvasive Assessment
of Alloimmunization
Fetuses are screened for risk of alloimmunization by
determining the Rh status of the parents. If the pregnant
woman is Rh negative, the father is screened. If the father
of the baby is also Rh negative, no further screening is
needed. If the mother is Rh negative and the father is
Rh positive, maternal antibody titers are monitored. If
they rise above 1:8, further testing is warranted. In
the past, this was done with amniocentesis assessing
for optical density (OD
) of amniotic fluid (hemolysis
50
increases OD of amniotic fluid), and serial PUBS was
performed as indicated to determine hematocrit (Hct).
Currently, Hct is indirectly inferred from middle cere-
bral artery (MCA) Doppler studies, in which peak systolic velocity (PSV) is elevated in cases of anemia (Video
41-5; see Chapter 43).
In response to severe anemia, the fetal circulation
becomes hyperdynamic with increased blood flow
velocities, which are thought to result from increased
cardiac output and decreased viscosity of fetal blood. In
addition, blood flow in the MCA may be increased
further because the brain circulation is known to respond
quickly to hypoxemia.
18
Although flow velocities in all
fetal vessels will be increased, the MCA is particularly
suitable for assessment because of its easy visualization
with color Doppler imaging as it courses directly above
the greater wing of the sphenoid bone, carrying more
than 80% of cerebral blood flow. The MCA has a highimpedance circulation with continuous forward flow.
The method for MCA Doppler includes finding the
circle of Willis, measuring a pulsed Doppler waveform
of the proximal MCA at the base of the brain, and
obtaining a PSV measurement with the angle of
insonation close to 0 degrees (Fig. 41-16, B). Intraobserver and interobserver variability is low.
In hypoxia, there is central redistribution of blood flow
with increased blood flow to the brain. This leads to
elevated PSV in cases of anemia. PSV is compared to
normed measures with respect to gestational age. Using
these thresholds, Zimmerman et al.19 found that overall
sensitivity to detect moderate to severe anemia at less than
35 weeks (hemoglobin <0.65 multiples of median) was
88%. Specificity was 87%; positive predictive value (PPV)
was 53%, and negative predictive value (NPV) was 98%.
It should be recognized that immune hydrops, even
untreated, is not uniformly lethal, and that transfusion
is not uniformly lifesaving. If fetuses with anemia and
hydrops are untreated, 34% of hydrops cases resolve
spontaneously, and 30% of fetuses die in utero. However,
if anemia is treated with intrauterine infusions, 53% of
hydrops cases resolve and 17.5% of fetuses die in utero.
When performing PUBS, it is important to check that
the mean corpuscular volume (MCV) is greater than
100 µm3 to prove that it is fetal blood being tested. The
hematocrit is checked to determine the amount of transfusion needed (Hct <30% is 2.5th centile >20 weeks).
To limit the amount of fluid being transfused into the
relatively small circulatory capacity of the fetus, packed
RBCs (type O negative; Hct >90%) are given. The goal
is to transfuse to Hct of 40 mL/dL. Successful treatment
of anemia with intravascular blood transfusion has been
reported as early as 13 weeks’ gestation.
20
A variable sign of anemia in the fetus is that of hepa-
tosplenomegaly. The fetal liver and spleen increase in
size because of their increased production of RBCs.
However, the fetus may be able to compensate for the
breakdown of RBCs and, in such cases, may have a large
liver and spleen, but would not necessarily be severely
anemic. Conversely, more rapid breakdown of RBCs may
prevent the fetus from adapting to hemolysis. Therefore,
anemia may develop without hepatosplenomegaly.
21,22
NONIMMUNE HYDROPS
Nonimmune hydrops occurs in 1:1500 to 1:4000 pregnancies. It is a common pathologic finding in first- and
second-trimester spontaneous abortions. The etiology
varies geographically and with gestational age. In North
America and Europe, most cases are cardiovascular (20%40%), infective (5%-10%), or chromosomal (16%;
usually Turner’s syndrome; trisomy 13, 18, and 21; triploidy) in origin.
gous α-thalassemia is a common cause;
carrier status for α-thalassemia occurs in 5% to 15% of
the population. Nonimmune hydrops in homozygous
α-thalassemia accounts for 25% of perinatal deaths in
Southeast Asia.
Pathophysiology
Nonimmune hydrops represents the terminal stage
for many conditions and is frequently multifactorial
(Table 41-1). Pathophysiology of hydrops may involve
increased hydrostatic pressure, high-output cardiac
failure, decreased plasma oncotic pressure, increased
capillary permeability, obstruction of lymph flow, or a
23,24
In Southeast Asia, however, homozy-
25
in this region,
1434 PART IV ■ Obstetric Sonography
TABLE 41-1. NONIMMUNE HYDROPS: COMMON CAUSES AND ASSOCIATIONS
EXAMPLES SUBCATEGORY EXAMPLES
Cardiovascular Structural heart disease Hypoplastic left or right heart syndrome
Myocarditis/cardiomyopathy
Valvular disease
Myocardial or pericardial tumors Tuberous sclerosis (e.g., rhabdomyoma)
Premature closure of foramen ovale or ductus arteriosus
Twin-twin transfusion syndrome
Arrhythmia Tachyarrhythmia
High-output cardiac failure Tumors such as maternal chorioangioma or fetal
Generalized arterial calcification
Lymphatics Abnormal lymphatic drainage
Neck Cystic hygroma
Chest Chylothorax/hydrothorax
Gastrointestinal Hepatic cirrhosis/fibrosis
Urinary tract Finnish nephrosis
Chromosomal 45,XO (Turner’s syndrome)
Hematologic
Infection Cytomegalovirus
Monochorionic twins Twin-twin transfusion syndrome (donor or recipient)
Myocardial infarction Anomalous left coronary artery
Congenital high airway obstruction
Congenital cystic adenomatoid malformation
Congenital diaphragmatic hernia
Pulmonary sequestration
Bronchogenic cyst
Congenital lymphedema
Hepatitis
Tumor
Portal vein thrombosis
Bowel atresia
Volvulus Malrotation with midgut volvulus
Meconium peritonitis
Urinary tract obstruction
Prune belly syndrome
Cloacal malformation
Renal vein thrombosis
Trisomy 21
Trisomy 18
Trisomy 13
Other aneuploidies
α-Thalassemia (homozygous)
Parvovirus
G6PD deficiency
Twin-twin transfusion (donor)
Congenital leukemia
Hemochromatosis
Inferior vena cava thrombosis
Parvovirus
Toxoplasmosis
Syphilis
Coxsackievirus
Adenovirus
Herpes simplex virus
Varicella
Acardiac twin (donor)
Atrioventricular canal
Atrioventricular septal defect
Transposition of great vessels
Tetralogy of Fallot
Ebstein anomaly
Bradyarrhythmia (including heart block)
sacrococcygeal teratoma
Vein of Galen malformation
Acardiac twin (donor)
Chapter 41 ■ Fetal Hydrops 1435
TABLE 41-1. NONIMMUNE HYDROPS: COMMON CAUSES AND ASSOCIATIONS—cont’d
EXAMPLES SUBCATEGORY EXAMPLES
Genetic Metabolic disorders Gaucher disease
Skeletal dysplasias Achondroplasia
Achondrogenesis
Osteogenesis imperfecta
Osteochondrodystrophy
Osteochondrodysplasia
Hypophosphatasia
Thanatophoric dysplasia
Asphyxiating thoracic dystrophy
Short-rib polydactyly syndrome
Fetal hypokinesis Arthrogryposis
Congenital myotonic dystrophy
Neu-Laxova syndrome
Pena-Shokeir syndrome
Other syndromes Noonan syndrome
Cornelia de Lange syndrome
Orofaciodigital syndrome
Idiopathic recurrent hydrops
Tumors Wilms’ tumor
Sacrococcygeal teratoma
Nephroblastoma
Neuroblastoma
Teratoma
Tuberous sclerosis
Arteriovenous malformation
Maternal Severe diabetes mellitus
Severe anemia
Severe hypoproteinemia
Indomethacin use (premature closure of ductus arteriosus)
Placental/cord Placental or umbilical vein thrombosis
Cord torsion, knot, or tumor
Umbilical artery aneurysm
Angiomyxoma of umbilical cord
Hemorrhagic endovasculitis of placenta
Chorioangioma
GM1 gangliosidosis
Sialidosis
Niemann-Pick disease types A and C
Mucopolysaccharidosis
Carnitine deficiency
Pyruvate kinase deficiency
Glucose phosphate isomerase deficiency
combination of these factors (Fig. 41-17). Fluid collections result from redistribution of fetal body fluids
among the intravascular, intracellular, and interstitial
compartments, secondary to an imbalance in capillary
ultrafiltration and interstitial fluid return.
26
Hypoxia and
circulatory failure may result in capillary damage that
leads to plasma protein and fluid loss from the intravascular compartment.
Several factors predispose to edema in the fetus versus
after birth. Both total body and extracellular fluid
compartments are proportionately greater in the fetus,
particularly at earlier gestational ages. Colloid osmotic
pressure is lower because of lower albumin concentrations. High compliance of the interstitial space facilitates
the accumulation of large volumes of fluid. Many causes
of fetal hydrops, especially those with a cardiac component, result from an increase in systemic venous pressure,
to which the fetus is particularly sensitive. In the fetus,
AnemiaArrhythmia
Cardiac failure
↑ Systemic
venous pressure
Venous or lymphatic
obstruction
Tissue hypoxia and
capillary leakage
HypoproteinemiaHydrops
FIGURE 41-17. Pathogenesis of hydrops.
Infection
Hepatocellular
damage
1436 PART IV ■ Obstetric Sonography
there is a net movement of fluid from the intravascular
to the extravascular space. Fivefold larger volumes of
fluid are removed by the lymphatics in fetal models than
in adult animal models. Thus, small elevations in systemic venous pressure (2-3 mm Hg) in the fetus can
substantially reduce lymphatic flow and can drive large
amounts of fluid into the extracellular space. This process
is further enhanced by the relatively greater permeability
of fetal capillaries to protein. The fetus is therefore particularly susceptible to small elevations in venous pressure from a number of causes, all of which can result in
hydrops.
12,13,24
Causes and Associations
Nonimmune hydrops is most commonly of a fetal etiology, but also may be caused by maternal or placental
factors (Table 41-1). Maternal causes (such as poorly
controlled diabetes mellitus) are rare and should be differentiated from maternal complications, which are secondary to fetal hydrops (termed mirror syndrome
because edema develops in the mother of an hydropic
fetus, “mirroring” the condition in the fetus).
27,28
Maternal thyrotoxicosis can cause fetal hyperthyroidism and
fetal hydrops, with potential for resolution of hydrops
after treatment with antithyroid drugs.
29
Placental
causes, such as chorioangioma and other vascular
shunts, are relatively rare and are usually associated with
high-output failure states and, in some cases, fetal
anemia.
30,31
Fetal metabolic causes are rare but important, because diagnosis can lead to appropriate neonatal
treatment and appropriate counseling of the patients
regarding recurrence risks.
A classification scheme for fetal causes is shown
in Table 41-1 and has some overlap in the groupings,
some of which may represent associations rather than
causations.
Cardiovascular Abnormalities
Cardiovascular abnormalities are the etiology of hydrops
in up to 40% of cases.
25,32
Hydrops is a rare complication
of isolated cardiac abnormality because the fetus has a
parallel flow circulation. In chromosomal abnormalities,
however, other factors with or without cardiac abnormality lead to hydrops.
Structural Cardiac Anomalies. In hydrops, cardiac
structural abnormalities may be causative or may be
found as associations
33
(Fig. 41-18). Right-sided lesions,
whether obstructive, such as pulmonary or tricuspid
atresia, or structural lesions that result in right atrial
volume or pressure overload, such as mitral regurgita-
tion, can result in congestive heart failure and hydrops.
34,35
Left-sided obstructive lesions, such as aortic stenosis,
mitral stenosis, and coarctation of the aorta, can result
in a hypoplastic left heart, causing increased blood flow
through the fetal right ventricle, which may result in
FIGURE 41-18. Hydrops secondary to structural
cardiac abnormality. Note the enlarged abnormal heart,
pleural effusions, and skin thickening.
hydrops.36 The presence of hydrops with congenital
structural heart disease carries a poor prognosis, with
survival as low as 17% for those with tricuspid disease
and hydrops.
37
Some fetuses with structural cardiac
anomalies also have rhythm disturbances, which contribute to the poor prognosis. In one series of 301 fetuses
with atrioventricular (A-V) septal defects, the presence
of fetal hydrops, together with bradycardia from sinus
node dysfunction or complete heart block, was associated with a poor outcome.
Cardiac Tumors. Cardiac tumors are a rare cause of
fetal hydrops.
39-44
Hydrops may be caused by several
38
mechanisms, depending on the tumor location, size, and
number. Cardiac lesions may cause obstruction to blood
flow and alteration of A-V valve function and may lead
to arrhythmia, cardiac tamponade, pericardial effusion,
and hydrops.
41-43
Rhabdomyomas are the most common fetal cardiac
tumor and are seen in association with tuberous sclerosis
in more than 80% of cases.
44
Rhabdomyomas are also
the most common cardiac tumors to cause hydrops.
Usually, these tumors are multiple, well circumscribed,
hyperechoic, and homogeneous and mainly involve the
ventricular myocardium
42
(Fig. 41-19). Rhabdomyomas
tend to grow during the second half of pregnancy,
most are diagnosed during the second and third trimesters. The location, size, and number of lesions correspond to risk for hydrops. Rhabdomyomas may cause
hydrops as a result of impaired diastolic filling, altered
A-V valve function, or outflow obstruction.
Intrapericardial teratomas are rare, usually appearing as cystic and solid masses outside the cardiac cavities,
arising from the pericardium. Teratomas may be larger
than the heart, and rapid growth of the tumor within
45
so
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