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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5786_Библиотеки_им_академика_М_И_Перельмана.pdf
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SCREENING AND DIAGNOSTIC STRATEGIES
Repeated ultrasound assessments are not feasible for all pregnant women and a
clinical selection of high-risk pregnancies is therefore needed. Accurate risk assessment and dating is therefore the first step before a confident ultrasound diagnosis
of fetal growth abnormalities. BPD and FL are rarely affected in growth disturbances and therefore their sensitivity in the detection of growth disturbances
is insufficient. For the screening of growth disturbances, most authors rely on
measurements of the AC since it reflects hepatic size and the amount of subcutaneous fat. The likelihood of a correct diagnosis increases as the percentile rank
decreases below the 10th percentile or increases above the 90th percentile. If normal values are based only on AGA fetuses, the 2.5th percentile is an appropriate
cut-off value but if normal values are based on the total population (LGA + AGA
+ SGA), the 10th percentile is more appropriate.24 The sensitivity is affected by the
choice of which percentile is used to define abnormality and by the GA which is
good at 34 weeks' gestation and poorer at 29–31 weeks.7 Abnormal values increase
the risk of growth disturbances even at a normal fetal weight estimation. For an
accurate diagnosis both the AC and estimated fetal weight should be abnormal.
24
FETAL GROWTH RESTRICTION
Fetal biometry, estimation of gestational age, assessment of fetal growth
The small size of the fetus is not a diagnosis by itself since it could occur when the
infant is actually sick from miscellaneous pathologies such as anatomical anomalies, genetic diseases, viral infections, placental and cord failure. In order to diagnose all these problems, other investigations are needed such as fetal morphology,
umbilical Doppler, fetal heart monitoring and biophysical profile supplemented
by invasive fetal testing for aneuploidy or viral infection. Oligohydramnios is
an important diagnostic and prognostic parameter in fetuses with IUGR but its
absence should not detract from the diagnosis. Umbilical Doppler velocimetry
is not useful as a screening technique for fetal growth restriction but once the
condition is diagnosed, it may reduce interventions and improve fetal outcome.
Whenever expectant management is indicated because of normal functional tests,
serial ultrasound biometry, 2–3 weeks apart, will allow a correct evaluation of the
true fetal growth. An AC growth rate of less than 10 mm/14 days has a sensitivity
of 85% and a specificity of 74% for detecting low birthweight.
MACROSOMIA
Risk factors of fetal macrosomia are diabetes, obesity and postdates. Sonographic
evaluation often overestimates birthweight, leading to an increase in caesarean
section rate, and should therefore be used with caution. However, an estimated
fetal weight of over 4200 g in a diabetic pregnancy with a dysproportioned size of
AC in comparison to other growth parameters should alert the clinician to consider an elective caesarean section. Such a policy might prevent shoulder dystocia
and its consequences without a relevant increase in caesarean section rate.
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Macrosomia has been found to be associated with an excessive growth rate
of the AC (>12 mm/week), a difference between abdominal diameter and BPD
greater than 26 mm and between thoracic diameter and BPD above 14 mm.
Subcutaneous tissue thickness has been studied as a predictor of macrosomia. The following parameters have been considered: cheek-to-cheek diameter,
humeral, shoulder, femoral and abdominal subcutaneous thickness, calculating
the most appropriate cut-off value with the ROC curve (from 11 to 13 mm). The
application of such measurements in clinical practice is still premature.
FETAL BIOMETRY, ANOMALIES AND SYNDROMES
The progressive alteration of single biometric values may indicate the presence
of fetal malformations as in cases of microcephaly or short-limbed dwarfism. In
many instances the diagnosis may not be apparent before the third trimester with
progressive alteration of biometric ratios below the first or above the 99th percentile. In such cases the number of SDs below or above the mean value (±3 SD)
Ultrasound in obstetrics and gynaecology
is more significant to indicate the degree of change in a particular biometric value
and the likelihood of a malformation than the percentile. The measurements of
some fetal parameters (nuchal translucency, short femur, short humerus) have
also been studied in the assessment of the risk of fetal aneuploidy.
20
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154
CONCLUSION
The careful measurement of selected fetal parameters throughout the pregnancy is the basis for obtaining some of the most important information of the
pregnancy, such as the gestational age and expected day of delivery, the size and
growth of the fetus and important information for the safe management of the
fetus before and after term as well as the delivery and birth.
References
1. Benacerraf BR, Gelman R, Frigoletto FD.
Sonographically estimated fetal weights:
accuracy and limitation. Am J Obstet
Gynecol 1988;159:1118–1121
2. Bettelheim D, Deutinger J, Bernascheck G.
Fetal sonographic biometry. Parthenon,
Carnforth, 1997
3. Chauhan SP, West DJ, Scardo JA, Boyd JM,
Joyner Y, Hendrix NV. Antepartum
detection of macrosomic fetus: clinical
versus sonographic, including softtissue measurements. Obstet Gynecol
2000;95:639–642
4. Crang-Svalenius E, Jorgensen C. Normal
ultrasonic fetal growth ratios evaluated in
cases of fetal disproportion. J Ultrasound
Med 1991;10:89–92
5. Deter RL, Harrist RB. Growth standards
for anatomic measurements and growth
rates derived from longitudinal studies of
normal foetal growth. J Clin Ultrasound
1992;20:381–388
6. Exacoustos C, Rosati P, Rizzo G, Arduini D.
Ultrasound measurements of fetal limb
bones. Ultrasound Obstet Gynecol
1991;1:325–330
7. Ferrazzi E, Nicolini U, Kustermann A,
Pardi G. Routine obstetric ultrasound:
effectiveness of cross-sectional screening for
fetal growth retardation. J Clin Ultrasound
1986;14:17–22
8. Gardosi J, Chang A, Kalyan B, Sahota D,
Simmonds EM. Customized antenatal
growth charts. Lancet 1992;339:283–287
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9. Hadlock FP, Deter RL, Harrist RB, Park SK.
Computer assisted analysis of fetal age in
the third trimester using multiple fetal
growth parameters. J Clin Ultrasound
1983;11:313–316
10. Hata T, Deter RL. A review of fetal organ
measurements obtained with ultrasound:
normal growth. J Clin Ultrasound
1992;20:155–174
11. Hill LM, Guzik D, Boyles D, Merolillo C,
Ballone A, Ghiter P. Subcutaneous tissue
thickness cannot be used to distinguish
abnormalities of foetal growth. Obstet
Gynecol 1992;80:268–271
12. Jeanty P, Beck GJ, Chevernak FA,
Kremkau FW, Hobbins JC. A comparison
of sector and linear array scanners for the
measurement of the fetal femur.
J Ultrasound Med 1985;4:525
13. Jeanty P. A simple reporting system for
obstetrical ultrasound examination.
J Ultrasound Med 1985;4:591–593
14. Jeanty P. Fetal biometry. In: Fleisher AC,
Manning FA, Jeanty P, Romero R (eds)
Sonography in obstetrics and gynecology.
Principles and practice. Prentice-Hall
International, New York, 1996: 131–149
15. Kurniawan YS, Deter RL, Visser GH,
Simon NV, van der Weele LT. Prediction
of neonatal crown–heel length from femur
diaphysis length measurements. J Clin
Ultrasound 1994;22:245–252
16. Manning FA. General principles and applications of ultrasonography. In: Creasy RK,
Resnik R (eds) Maternal-fetal medicine, 4th
edn. WB Saunders, Philadelphia, 1999:
169–206
17. Miller JM, Kissling GA, Brown HL,
Gabert HA. Estimated fetal weight:
applicability to small- and large-forgestational-age fetus. J Clin Ultrasound
1988;16:95–97
18. Mongelli M, Wilcox M, Gardosi J.
Estimating the day of confinement:
ultrasonographic biometry versus certain
menstrual dates. Am J Obstet Gynecol
1996;174:278–281
19. O'Keeffe DF, Garite TJ, Elliott JP, Burns PE.
The accuracy of estimated gestational
age based on ultrasound measurement of
biparietal diameter in preterm premature
rupture of the membranes. Am J Obstet
Gynecol 1985;151:309–312
20. O' Reilly-Green, Divon M. Sonographic
and clinical methods in the diagnosis
of macrosomia. Clin Obstet Gynecol
2000;43:309–320
21. Sabbagha RE, Hughey M, Depp R. The
assignment of growth-adjusted sonographic
age (GASA): a simplified method. Obstet
Gynecol 1978;51:383–386
22. Stebbins B, Jaffe R. Fetal biometry and
gestational age estimation. In: Jaffe R, Bui
TH (eds) Textbook of fetal ultrasound.
Parthenon, Carnforth, 1999: 47–57
23. Thompson TE, Manning FA, Morrison I.
Determination of fetal volume in utero by an
ultrasound method: correlation with neonatal
birth weight. J Ultrasound Med 1983;2:113
24. Weiner CP, Robinson D. The sonographic
diagnosis of intrauterine growth retrdation
using the postnatal ponderal index and the
crown–heel length as standards of diagnosis.
Am J Perinatol 1989;6:380–383
25. Zelop CM. Prediction of fetal weight
with the use of three-dimensional
ultrasonography. Clin Obstet Gynecol
2000;43:321–325
26. Tunon K, Eik-Nes SH, Grottum P.
A comparison between ultrasound and a
reliable menstrual period as predictors of
the day of delivery in 15000 examinations.
Ultrasound Obstet Gynecol 1996;8:
178–185
Fetal biometry, estimation of gestational age, assessment of fetal growth
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Prenatal diagnosis of fetal anomalies
Gianluigi Pilu Kypros H Nicolaides Israel Meizner
Roberto Romero Waldo Sepulveda
ABSTRACT
Congenital anomalies occur in about 2.5% of all births and are the leading
cause of infant mortality and probably of long-term handicap. A well-performed
ultrasound examination carried out around midgestation allows identification
of about 50% of all major anomalies. Ultrasound may also help in identifying
aneuploidies at midgestation, although the specific approach remains
controversial. The distinctive features of the sonographic diagnosis of anomalies,
as well as the clinical implications, are discussed.
KEYWORDS
Chromosomal aberrations, congenital anomalies, fetus, prenatal diagnosis,
ultrasound.
AN INTRODUCTION TO CONGENITAL ANOMALIES
Detection of fetal anomalies is one of the major reasons motivating the use of
ultrasound in pregnancy. Congenital anomalies are the leading cause of infant mortality and probably one of the leading causes of long-term morbidity. Diagnosis of
fetal anomalies is far from simple. It demands expertise in obstetrical ultrasound
as well as knowledge in many fields including anatomy, embryology, teratology,
genetics, paediatrics and cardiology. There is, however, consensus that a wellperformed basic ultrasound scan, including the evaluation of a well-defined set of
quantitative and qualitative parameters, can detect the presence of a substantial
number of anomalies, thus allowing the patient to undergo a targeted examination in a centre. The elements of the basic evaluation of fetal anatomy have been
discussed in a previous chapter. The proportion of anomalies that will be detected
by a basic ultrasound survey of fetal anatomy is controversial, as various studies
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have reported very different results, and we will summarize the available experience at the end of this chapter.
Our aim is to review the frequency and impact of congenital anomalies and
to provide basic concepts useful for ultrasound identification. Diagnosing fetal
anomalies is difficult and we refer the interested readers to the many detailed
textbooks available on the subject.
A congenital anomaly consists of a departure from the normal anatomical architecture of an organ or system. Anomalies may result from an intrinsically abnormal primordium (malformation) or from a normal primordium that is affected
during development by extrinsic forces, such as vascular accidents (disruptions)
or mechanical compression (deformations).
Although there are several systems used to classify congenital anomalies, a
common method is to divide them into major and minor. A major anomaly is
one with medical, surgical or cosmetic importance and with impact on morbidity and mortality. A minor anomaly is one that does not have a serious surgical,
medical or cosmetic significance, and does not affect normal life expectancy or
lifestyle. Obviously, this classification is subjective and arbitrary. There is an over-
Ultrasound in obstetrics and gynaecology
lap between minor anomalies and normal anatomical or phenotypical variants.
A phenotypical variant occurs with a frequency of more than 4% in the general
population, whereas minor anomalies occur with a rate of less than 4%. Clearly,
this is also an arbitrary definition.
The precise incidence of congenital anomalies is difficult to determine. Accurate
documentation depends on many factors including:
1–4
158
age at examination (prenatal period, newborn period, infancy or later in
•
life)
the experience of the observer (e.g. general paediatrician versus
•
dysmorphologist)
the definition of an anomaly (major, minor, normal phenotypical variation)
•
the type of examination (body surface examination, extensive examination
•
including evaluation of internal organs)
ethnic, geographical and social variations in the incidence of individual
•
malformations.
There is a general consensus that the prevalence of anomalies detected at birth
is in the region of 2.5%, while long-term follow-up studies demonstrate much
higher figures, in the range of 14–15%. It is important to remember that even
severe anomalies may not be detected at birth; for example, some cardiac abnormalities will only be manifest afterwards. The neurological examination of a newborn infant has many limitations, and severe central nervous system anomalies
may be undetected up to 1–3 years of age.
Causative factors for congenital malformations may be identified in
approximately 40% of cases and are usually divided into four major groups:
single gene disorders, chromosome abnormalities, multifactorial conditions
(involving both environmental and genetic components), and environmental
factors. About 7.5% of all congenital malformations are caused by a single gene
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mutation.
5,6
Autosomal mutations occur when the gene is located in a non-sex
chromosome and may be either dominant (e.g. adult polycystic kidney disease,
achondroplasia) or recessive (e.g. infantile polycystic kidney disease, achondrogenesis, short-rib polydactyly syndrome). Autosomal dominant conditions
have a recurrence risk of 50% for the subsequent offspring, whereas autosomal
recessive conditions have a recurrence risk of 25%. The term X-linked disorder is reserved for single gene mutations in the X chromosome (e.g. fragile X
syndrome, fetal akinesia syndrome, oto-palato-digital syndrome). In this case,
women are asymptomatic carriers and the disease is usually expressed only
in males. Chromosomal anomalies are responsible for about 6% of all serious
congenital malformations among live-born infants. They may be numerical or
structural in nature. Multifactorial conditions are responsible for 20% of malformations in live-born fetuses. Examples of malformations with a multifactorial inheritance include spina bifida, cleft lip/palate and congenital dislocation
of the hip. These anomalies are the result of interactions between a relatively
large number of genes with similar effects and non-genetic, usually undefined
factors. Currently, 2–3% of the spectrum of congenital malformations is attributed to teratogens, with most malformations resulting from exposures during
days 18–40 post conception, except for the palate, central nervous system and
genital structures that can be affected at later stages of development.
Finally, a significant proportion of congenital malformations of unknown aetiol-
ogy are likely to be polygenic or at least have an important genetic component.
5,6
Congenital anomalies are an important determinant of perinatal and infantile death and long-term morbidity. A substantial fall in maternal and infant
mortality rates was achieved during the 20th century. Environmental interventions, improvements in nutrition, advances in clinical medicine, wider access to
healthcare, increased surveillance and monitoring of disease, better education
and higher living standards contributed to this accomplishment. In Scotland,
the overall perinatal mortality declined by 75% between the periods 1939–
1941 and 1974–1976, but over the same 37-year time span, the contribution of
congenital anomalies to perinatal mortality increased from 10% to 25%.
7
From
1915 to 1997, while the United States experienced a 93% drop in infant mortality (from approximately 100/1000 to 7.2/1000 live births),8 the relative contribution of congenital anomalies to the perinatal death rate increased. In 1995,
according to the Centers for Disease Control and Prevention, birth defects were
the leading cause of infant mortality in the USA.
9,10
From 1968 to 1995, the
proportion of infant deaths attributable to birth defects increased from 15% to
11,12
22%.
Alongside the impact caused by congenital anomalies in perinatal mortality,
there is an increased awareness regarding the role of congenital disease in determining morbidity. It has been estimated that at least 1% of all hospital admissions
have a genetic basis or genetic contribution to their disease; as many as one of
every four hospitalized children is affected by a disease that is at least partially
genetically determined and approximately one of every 20 children is affected by
a disorder that is completely genetic in origin. Infants with anomalies detected
Prenatal diagnosis of fetal anomalies
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Ventriculomegaly
Mild
Severe
Anterior midline defects
Alobar
holoprosencephaly
Lobar
holoprosencephaly
Agenesis of
corpus callosum
within the first year have a significant increase in the risk of death and in all
parameters of evaluated postnatal morbidity. Infants with congenital anomalies
also impose an economic burden on society and contribute stress to the family
nucleus. For example, the incidence of divorce and sibling social maladjustment is
greater in families of children with spina bifida than in families of infants without
congenital anomalies.
CENTRAL NERVOUS SYSTEM ANOMALIES
Most cerebral anomalies diagnosable in utero by ultrasound are easily demonstrated by the use of two transverse sections of the fetal head, one obtained at
the level of the lateral ventricles (transventricular plane) (Fig. 10.1) and the other
at the level of basal ganglia and cerebellum (Fig. 10.2). Recently, magnetic resonance imaging has become a valuable tool in the diagnosis of suspected brain and
spine abnormalities.
Ultrasound in obstetrics and gynaecology
31,32
160
Fig. 10.1 Fetal cerebral anomalies detectable with the transventricular plane.
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Absent cisterna magna
banana sign
(spina bifida)
Large cisterna magna
cerebellar defect
(Dandy–Walker complex)
Normal
cisterna magna
Prenatal diagnosis of fetal anomalies
Fig. 10.2 Fetal cerebral anomalies detectable with the transcerebellar view.
NEURAL TUBE DEFECTS
These include anencephaly, spina bifida and encephalocele. In anencephaly there
is absence of the cranial vault (acrania) with secondary degeneration of the brain.
Encephaloceles are cranial defects, usually occipital, with herniated fluid-filled or
brain-filled cysts. In spina bifida the neural arch, usually in the lumbosacral region,
is incomplete with secondary damage to the exposed nerves. The incidence of
neural tube defects is subject to large geographical and temporal variations; in
Europe the prevalence is about 1–2 per 1000 births with a peak of 5 per 1000
births. Anencephaly and spina bifida, with an approximately equal prevalence,
account for 95% of cases and encephalocele for the remaining 5%. Neural tube
defects are multifactorial disorders. Chromosomal abnormalities, single mutant
genes and maternal diabetes mellitus or ingestion of teratogens, such as antiepileptic drugs, are implicated in about 10% of cases. When a parent or previous sibling has had a neural tube defect, the risk of recurrence is 5–10%. Periconception
supplementation of the maternal diet with folate reduces by about half the risk
of developing these defects.
The sonographic diagnosis of anencephaly during the second trimester of pregnancy is based on the demonstration of absent cranial vault and cerebral hemispheres. The diagnosis can be made after 11 weeks, when ossification of the skull
161
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normally occurs. Ultrasound reports have demonstrated that there is progression
from acrania to exencephaly and finally anencephaly. In the first trimester the
pathognomonic feature is acrania, the brain being either entirely normal or with
varying degrees of distortion and disruption.
Diagnosis of spina bifida requires the systematic examination of each neural
arch from the cervical to the sacral region both transversely and longitudinally.
In the transverse scan the normal neural arch appears as a closed circle with an
intact skin covering, whereas in spina bifida the arch is U-shaped and there is
an associated bulging meningocele (thin-walled cyst) or myelomeningocele. The
extent of the defect and any associated kyphoscoliosis are best assessed in the
longitudinal scan (Fig. 10.3).
The diagnosis of spina bifida has been greatly enhanced by the recognition of associated abnormalities in the skull and brain. These abnormalities
include frontal bone scalloping (lemon sign) and obliteration of the cisterna
magna with either an ‘absent’ cerebellum or abnormal anterior curvature of
the cerebellar hemispheres (banana sign). These easily recognizable alterations
in skull and brain morphology are often more readily attainable than detailed
Ultrasound in obstetrics and gynaecology
spinal views.13 A variable degree of ventricular enlargement is present in virtually all cases of open spina bifida at birth, but in only about 70% of cases in
the midtrimester.
Closed spina bifida may be associated with neurological compromise and the
prenatal diagnosis is difficult, because α-fetoprotein is usually within normal limits
in both amniotic fluid and maternal serum, there are no cranial signs and the spinal defect may be small and difficult or impossible to identify sonographically.
Encephaloceles are recognized as cranial defects with herniated fluid-filled or
brain-filled cysts. They are most commonly found in an occipital location (75% of
cases) but alternative sites include the frontoethmoidal and parietal regions.
Anencephaly is fatal at or within hours of birth. In encephalocele the prognosis is inversely related to the amount of herniated cerebral tissue; overall the
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Fig. 10.3 Lumbosacral myelomeningocele in the sagittal (left) and axial (right) view.
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neonatal mortality is about 40% and more than 80% of survivors are intellectually and neurologically handicapped. In spina bifida, surviving infants are often
severely handicapped, with paralysis in the lower limbs and double incontinence; despite the associated hydrocephalus requiring surgery, intelligence may
be normal.
VENTRICULOMEGALY
The term ventriculomegaly is commonly used to indicate enlargement of the lateral cerebral ventricles. The incidence of this finding is unclear. Severe ventriculomegaly or hydrocephalus is found in less than 1 per 1000 births. Ventriculomegaly
may be the consequence of cerebral malformations, chromosomal abnormalities
or congenital infection. Genetic factors play an important role. About 25% of
severe ventriculomegaly occurring in males is due to X-linked transmission.
Fetal ventriculomegaly is diagnosed sonographically, by the demonstration of
abnormally dilated lateral cerebral ventricles. A transverse scan of the fetal head
at the level of the cavum septum pellucidum will demonstrate the dilated lateral
ventricles, defined by an internal diameter of the posterior horn (or atrium) of
10 mm or more.13 The choroid plexuses, which normally fill the lateral ventricles,
are surrounded by fluid. A diameter of 10–15 mm indicates mild ventriculomegaly.
A diameter greater than 15 mm indicates moderate to severe ventriculomegaly.33
Certainly before 24 weeks and particularly in cases of associated spina bifida, the
head circumference may be small rather than large for gestation.
Fetal or perinatal death and neurodevelopment in survivors are strongly related
to the presence of other malformations and chromosomal defects.34 Isolated severe
ventriculomegaly is associated with an increased risk of perinatal death and a 50%
chance of neurological sequelae in survivors. Although isolated mild ventriculomegaly (atrial width of 10–15 mm) is generally associated with a good prognosis, it
is also the group with the highest incidence of chromosomal abnormalities (often
trisomy 21). In addition, in a few cases with apparently isolated mild ventriculomegaly there may be an underlying cerebral maldevelopment (such as lissencephaly) or destructive lesion (such as periventricular leukomalasia). It has been
suggested that ventricles of 10–12 mm, which represent the bulk of these cases,
tend to have a good prognosis, with neurological compromise in the range of 4%,
while those cases in which the measurement is 13–15 mm are associated with a
greater probability of handicap, in the range of 12%.
Prenatal diagnosis of fetal anomalies
HOLOPROSENCEPHALY
This is a spectrum of cerebral abnormalities resulting from incomplete cleavage of the forebrain. There are three types according to the degree of forebrain
cleavage. The alobar type, which is the most severe, is characterized by a monoventricular cavity and fusion of the thalami. In the semilobar type there is partial
segmentation of the ventricles and cerebral hemispheres posteriorly with incomplete fusion of the thalami. In lobar holoprosencephaly there is normal separation
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