HYDROPS FETALIS LAB STUDIES
Category: Child Health
Abstract : hydrops fetalis Lab Studies: • Diagnostic studies may be considered best by
temporal grouping (ie, fetal, maternal, placental, neonatal, postmortem).
Assessments generally proceed from low-risk noninvasive tests to higher-risk
invasive techniques as required for precise and complete diagnosis to properly
manage the individual pregnancy. • Obtain several maternal laborator
hydrops fetalis Lab Studies:
• Diagnostic studies may be considered best by
temporal grouping (ie, fetal, maternal, placental, neonatal, postmortem).
Assessments generally proceed from low-risk noninvasive tests to higher-risk
invasive techniques as required for precise and complete diagnosis to properly
manage the individual pregnancy.
• Obtain several maternal laboratory studies
concurrent with the initial fetal imaging assessment.
o Assessment of
maternal blood type (red cells) and antibody screen (identification, and
quantitation when indicated, of maternal plasma antibodies) are standard
screening tests recommended in most guidelines for prenatal care. Over the past
few years, the introduction of new molecular genetic techniques (PCR) has
demonstrated considerable promise; however, definitive comparisons with standard
methods are not yet available. More than 85% of Rh-sensitized women whose anti-D
titers were 1:512 or higher were found to be HLA type DQBI allele*0201. Although
this single study suggests that HLA typing may be of value in the prospective
management of isoimmunization, this observation requires confirmation and
further study.
o Qualitative and quantitative estimates of the proportion
of red cells containing fetal hemoglobin in the maternal circulation are of
particular value.
The Betke-Kleihauer technique depends on the different
vulnerability of cells containing fetal hemoglobin from those with adult
hemoglobin when subjected to acid-elution.
A newer method using flow
cytometry has also been found to be useful.
Results using either method
must be interpreted with considerable caution, since poor sensitivity and
specificity of these diagnostic tests has been demonstrated in several
studies.
o The search for maternal-fetal infection must be intensive.
Syphilis serology was a standard prenatal screening test for decades. More
recently, the test has been used more selectively, despite the absence of any
good evidence for this change. If fetal hydrops is suspected, syphilis serology
is mandatory with repeat serial testing and, very importantly, with dilution of
maternal serum. The prozone effect has been demonstrated repeatedly with fetal
hydrops due to syphilis, thus dilution of maternal serum to avoid false-negative
results is required.
o Antibody screens for common fetal infections
(toxoplasmosis, other infections, rubella, CMV infection, and herpes simplex
[TORCH]) and more sensitive and specific enzyme-linked immunosorbent assay
(ELISA) studies for individual infectious agents have been used for many years.
More recently, the PCR technique generally is accepted as the criterion standard
and should be employed whenever possible.
o Hemoglobin electrophoresis
for alpha-thalassemia heterozygosity has been useful in ethnically at-risk
populations. In regions where ethnic diversity is high, routine screening may be
preferable to selection based on ethnicity. More recently, PCR screens and
colorimetric monoclonal antizeta antibody tests for heterozygote
alpha-thalassemia have been demonstrated as economically feasible screening
procedures.
o Maternal serum screening tests (multiple-marker,
triple-screen, triple-marker), commonly used if fetal anomaly is suspected, are
of uncertain value with fetal hydrops.
In one study, positive screening
tests (any of the 3 used) with a sensitivity of only 60% in 19 cases of Turner
syndrome distinguished some fetuses with cystic hygroma and/or hydrops from
those without. Individual components of these tests were examined separately in
several other studies.
Elevated AFP levels have been reported in hydrops
associated with fetomaternal hemorrhage, umbilical cord hemangioma, polycystic
kidneys, CMV, and Parvovirus; however, AFP levels are similar in babies with
Turner syndrome with or without hydrops. Use of AFP screening as an index of
fetal aplastic crisis in maternal Parvovirus infection has been recommended but
is of dubious value, since several fetal deaths have been observed with AFP
levels within reference range. The precise diagnostic value of AFP screening is
uncertain, since definitive studies are not available.
Low levels of
unconjugated estriol (uE3) have been found in one hydropic baby with
Smith-Lemli-Opitz syndrome, but the test has not demonstrated value in
distinguishing between babies with or without hydrops, and normal levels have
been observed in several hydropic deaths.
Human chorionic gonadotropin
levels have been reported as significantly elevated in hydrops with
sacrococcygeal teratoma, choriocarcinoma, Parvovirus, Turner syndrome, and Down
syndrome; however, these levels have also been normal in several hydropic fetal
deaths related to Parvovirus.
In a single study, inhibin-A levels were
elevated markedly in 12 fetuses with Turner syndrome with hydrops and were
reduced significantly in those fetuses without hydrops. Maternal serum IgG
placental alkaline phosphatase levels are increased with fetal hydrops;
currently, clinical utility of this finding is untested.
• Direct
invasive sampling studies of fetal AF or placental tissues or fluids have
demonstrated value for definitive diagnosis, monitoring of treatment efficacy,
and accurate prognosis in a number of conditions associated with
hydrops.
o Elevated levels of AF bilirubin, as measured by the
spectrophotometric extrapolation technique first described by Liley, have been
demonstrated to be highly sensitive predictors of the severity of fetal anemia
due to isoimmunization.
Specificity is somewhat less, since alpha-feto
bilirubin may also be elevated due to maternal hemoglobinopathy or hepatitis and
in association with impaired fetal swallowing due to fetal gastrointestinal
obstruction and a number of fetal central nervous system disorders.
Recent
reports have suggested the use of sonographic methods to detect fetal anemia;
however, routine use of such noninvasive methods is not justified in the absence
of definitive evidence of their superior sensitivity and specificity, at less
risk, when compared with the standard proven method of AF bilirubin
analysis.
o Direct enzyme assays or biochemical analyses of measurements
of levels of specific metabolic products may be indicated in the pregnancy at
risk of hydrops because of inborn errors of metabolism.
Such studies may
use samples from the mother and father (red cells, serum, urine, tissue), fetus
(skin fibroblast cultures or leukocytes from AF, fetal red cells, white cells,
serum samples from direct cordocentesis, serous effusions), placenta (chorionic
villous sampling, placental biopsy), or AF.
Examples include biochemical
analyses of urine or AF for abnormal oligosaccharide, mucopolysaccharide, and
sphingolipid metabolites when lysosomal disorders are suspected or determination
of AF 7-dehydrocholesterol reductase if history and findings suggest
Smith-Lemli-Opitz syndrome.
o Fetal serum endothelin levels are elevated
more than 2-fold in recipients; however, these levels are normal in donors with
twin-twin transfusion syndrome. Endothelin levels were related to presence of
and severity of hydrops in these cases. Changes in fetal serum liver enzymes,
particularly alanine transaminase and glutamyl transpeptidase, have been
demonstrated to occur following correction of the anemia by fetal transfusion.
Whether or not these observations may be of diagnostic or prognostic use is
currently untested. o Direct fetal diagnostic studies for Parvovirus include
histologic staining methods (RBC), digoxigenin-labeled B19. DNA probe (PCR), and
avidin-biotin complex immunohistochemical and immunofluorescent studies, among
others. Currently, PCR methods appear to be best, although definitive studies
providing sensitivity and specificity are not available.
o Karyotyping is
always indicated if history or ultrasound results reveal a constellation of
findings consistent with a chromosomal aberration or if maternal or family
history is suggestive.
Chromosome studies are indicated whenever initial
diagnostic studies have failed to identify with certainty a specific cause for
the fetal hydrops.
Chromosomal analyses may be performed on desquamated
fetal epithelial cells in AF, fetal tissue biopsy samples, or placental (fetal
tissue) biopsy samples.
An increase in AFP has been observed in almost 1
in 10 (8.4%) genetic amniocenteses; fetal mortality exceeded 1 in 10 (14%) when
such AFP elevations occurred. Evidence of fetomaternal bleeding is present in 3
of 4 chorionic villous samplings. Thus, careful weighing of benefit versus risk
must be made whenever direct invasive diagnostic methods are
considered.
o To obtain more precise information concerning fetal status,
direct fetal sampling by cordocentesis (or periumbilical sampling) has been used
with increasing frequency.
Acidemia, hypoxemia, and hypercarbia are found
in most studies of fetal acid-base balance and blood-gas status obtained at time
of direct fetal treatment. These results are nonspecific and anticipated and,
while they may be of use in immediate management, are unlikely to be of value in
longer-term care of the fetus with hydrops.
Analyses of serous effusion
fluids (pleural, pericardial, or ascitic, most commonly) have been of
surprisingly little value. For example, lymphocyte counts considered
characteristic of congenital chylothorax when found in the newborn infant have
been observed in pleural effusions from fetuses with CMV disease.
Serologic tests for specific infections, hemoglobin or hematocrit measurements,
platelet counts, white cell counts and morphologic analyses, specific enzyme
analyses, and karyotyping are just a few of the more common measurements
obtained. While this information may be invaluable in specific cases, use of
such invasive methods on a routine basis carries significant risks.
Fetal
sampling by cordocentesis is followed by significant bradycardia in almost 1 in
20 samplings (3.8%); of those with such complications, almost two thirds die
(61.5%). o Elevated AF alkaline phosphatase has been observed in association
with fetal hydrops due to Turner syndrome; while likely to be a nonspecific
finding, further study is necessary.
• The fetal biophysic profile has
been demonstrated to be abnormal in severe fetal hydrops.
o Cardiotocographic
records obtained 12 hours prior to fetal death demonstrate absence of short-term
and long-term variability, absence of tachycardia, presence of late
decelerations, and terminal bradycardia.
o Sinusoidal heart-rate patterns
have been observed consistently in hydrops associated with severe fetal anemia
related to isoimmunization and fetomaternal hemorrhage.
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