ANTENATAL ULTRASOUND SCREENING FOR ANOMALIES AMONG SINGLETONS
– RESULTS OF A PROSPECTIVE STUDY
Balakumar.K
Balku's Scan
Address
for Correspondence
Dr.Balakumar.K
Balku's Scan
PVS Hospital, Calicut, Kerala 673 002.
E mail : balkumardr@sify.com
ABSTRACT
A
prospective study of 15 years and 7 months duration was carried
out to define the incidence and systemic distribution of fetal
anomalies in Kerala (a southwestern coastal state of India). Among
the live 30, 030 singleton pregnancies of 9 to 41weeks’
gestation subjected to ultrasound scanning, the incidence of major
fetal anomalies was found to be 2.59% (p < 0.05). The central
nervous system was the commonest involved (39.21%), followed by
the genitourinary tract (18.09%) and the skeletal system (11.79%)
anomalies. The incidence of neural tube defects was 17.27%. A
significant number of fetuses showed acrania (0.82%) and jugular
lymphatic obstruction sequence (2.57%). The sensitivity and the
specificity values of the screening results were 72.2% and 98.6%
respectively. The single author has carried out the observation
and analysis.
KEY
WORDS: Fetal
anomalies, prenatal diagnosis, ultrasonography, ultrasound scan,
antenatal screening.
AIM
The study was aimed at defining the incidence of major
fetal anomalies in northern Kerala that could be detected by
routine ultrasound scanning. The quantification of the true
incidence and the definition of the systemic preponderance help in
stratification of the affected fetuses for the sake of
prognostication and tailoring of management policies.
MATERIALS
AND METHODS
Those pregnancies referred for routine as well as targeted
imaging contributed the population for this study. Only live
singleton pregnancies of 9 to 41 weeks' gestation were analysed.
Plural pregnancies were excluded because of statistically lower
number. The amniotic fluid volume was assessed subjectively. Those
with vesicular mole and intrauterine demise were excluded.
Metabolic diseases and other abnormalities without evident
structural variations were also excluded. Minor anomalies of
minimal surgical or cosmetic significance were not included. The
fetuses were selected at random. Those with major anomalies were
serially assessed and followed up for confirmation of the
diagnosis. Suspicious findings were verified from peroperative
findings, autopsy or follow up records.
The machines used were Philips SDR 1550 and Philips P 600 (transabdominal
linear convex probes of 3 - 3.5 and transvaginal probe of 5.5 -
6.5 MHz along with color Doppler facilities). The total population
studied was 34, 240 fetuses of which 33, 030 were singletons and
1, 210 were plural pregnancies. The single author has conducted
this prospective study from January1985 through August 2000 (15
years and 7 months).
OBSERVATIONS
The majority of the cases referred for scanning were for
confirmation of the gestational age and for exclusion of
associated pathologies and anomalies. A more specific indication
was the disproportionate uterine size compared to the period of
amenorrhoea. The other common indications were vaginal bleeding
and discrepancies of growth. Those mothers with history of
previous anomalous fetuses, perinatal infections or exposure to
teratogens formed only a small group.
Polyhydramnios of moderate to severe degree was noted in
450 pregnancies of the total sample studied. The central nervous
system and gastrointestinal system were commonly involved in these
cases. No ultrasonographically detectable cause could be defined
in few. Significant degree of oligohydramnios was seen in 85
pregnancies. Genitourinary tract anomalies were found as the major
contributor for this. Pregnancies with severe degree
oligohydramnios often ended up with early intrauterine demise, so
that the cause was unidentifiable by echoes in many instances.
There were 857 anomalous fetuses in the population studied.
The system wise distribution is represented in the Chart No.1. The
smaller entities were grouped as “others”,
including
lymphatic and respiratory system anomalies. The details are shown
in the Table No. 1.
Chart
No.1 showing the systemic distribution
|
Systems
involved
|
No.
of fetuses affected
|
Percentage
|
|
CNS
|
336
|
39.21
|
|
GUT
|
155
|
18.09
|
|
SKELETAL
SYSTEM
|
101
|
11.79
|
|
GIT
|
091
|
10.62
|
|
CVS
|
045
|
05.25
|
|
OTHERS
|
129
|
15.05
|
|
TOTAL
|
857
|
02.59
% (overall)
|
Table No.1. Details of systemic involvement among 33,030
live singletons.
The commonest system involved was the central nervous
system (CNS) in 336 fetuses. The neural tube defects (NTD) were
diagnosed in 148 and among them anencephaly was seen in 108
fetuses. There were 14 fetuses with cephaloceles, 11 with
meningomyeloceles and 6 with spina bifida. Acrania (exencephaly)
was diagnosed in 7 fetuses of first trimester. Hydrocephalus was
evident in 104 fetuses. Twenty-five fetuses showed microcephaly
and an equal number had holoprosencephaly. The CNS anomalies are
detailed in the following table No.2.
|
CNS
anomalies
|
No.
of fetuses affected
|
Percentage
|
|
Anencephaly
|
108
|
12.60
|
|
Cephalocele
|
14
|
1.63
|
|
Meningo\
myelocele
|
11
|
1.28
|
|
Spina
bifida
|
06
|
0.70
|
|
Iniencephaly
|
02
|
0.23
|
|
Acrania
|
07
|
0.82
|
|
Hydrocephalus
|
104
|
12.14
|
|
Dandy
Walker Malformation
|
07
|
0.82
|
|
Arnold
Chiari malformation
|
04
|
0.47
|
|
Corpus
callosal agenesis
|
02
|
0.23
|
|
Microcephaly
|
25
|
2.92
|
|
Holoprosencephaly
|
25
|
2.92
|
|
Porencephaly
|
05
|
0.74
|
|
Hydranencephaly
|
03
|
0.35
|
|
Schizencephaly
|
03
|
0.35
|
|
Kyphosis
|
03
|
0.35
|
|
Teratoma
|
03
|
0.35
|
|
Arachnoid
cyst
|
03
|
0.35
|
|
Choroid
plexus cyst (bilateral)
|
03
|
0.35
|
|
Total
|
336
|
39.20
%
|
Table
No. 2. The distribution of the CNS anomalies
The genitourinary tract (GUT) anomalies were diagnosed in
154 fetuses (Table No.3). Among them, hydronephrosis was seen in
81 fetuses. Fetuses with dilated renal pelves of less than 8 mm
before 32 weeks and less than 10 mm after 32 weeks were excluded
from this study. The cystic renal diseases were documented in 25
fetuses. The commonest presentation was the presence of multiple
cysts of varying size. The diagnosis of infantile polycystic
kidney disease (IPKD) could be specifically made on typical
sonographic features. Bladder outlet obstruction was detected in
22 fetuses. There were 14 fetuses having renal agenesis in
association with severe degree oligohydramnios. Five fetuses
showed megacystis leading to massive distension of the abdomen.
Ureterocele was diagnosed in a fetus of 36 weeks gestation causing
unilateral hydronephrosis. Only one fetus showed ectopia vesica.
|
GUT
anomalies
|
No.
of fetuses affected
|
Percentage
|
|
Hydronephrosis
|
81
|
9.45
|
|
Cystic
kidneys
|
25
|
2.92
|
|
Bladder
outlet obstruction
|
22
|
2.57
|
|
Renal
agenesis
|
14
|
1.63
|
|
Megacystis
|
05
|
0.58
|
|
Echogenic
kidneys
|
06
|
0.70
|
|
Extrophy
|
01
|
0.12
|
|
Ureterocele
|
01
|
0.12
|
|
TOTAL
|
155
|
18.08
%
|
Table
No. 3. Distribution of GUT anomalies
Skeletal system was involved in 101 fetuses (Table No.4).
The commonest presentation was as limb reduction abnormalities in
56. There were 16 cases of achondroplasia, 8 cases of
achondrogenesis, 4 cases of osteogenesis imperfecta and 3 cases of
thanatophoric dysplasia. Thoracic dysplasia was the main
presentation in 13 fetuses. Only one fetus showed the classical
predictors of hypophosphatasia. A more precise typing of the
fetuses with limb shortening was difficult antenatally.
|
SKELETAL
anomalies
|
No.
of fetuses affected
|
Percentage
|
|
Limb
bone shortening
|
56
|
6.53
|
|
Achondroplasia
|
16
|
1.87
|
|
Achondrogenesis
|
08
|
0.93
|
|
Osteogenesis
imperfecta
|
04
|
0.47
|
|
Thanatophoric
dysplasia
|
03
|
0.35
|
|
Thoracic
dysplasia
|
13
|
1.52
|
|
Hypophosphatasia
|
01
|
0.12
|
|
TOTAL
|
101
|
11.78
%
|
Table
No. 4. The distribution of skeletal system anomalies
The gastrointestinal tract (GIT) anomalies in 91 fetuses
(Table No. 5) showed a preponderance of esophageal
(26 fetuses) and intestinal atresias (25 fetuses).
Diaphragmatic hernia was diagnosed in 25 fetuses. All of then
presented with considerable degree of polyhydramnios. There were 8
fetuses with omphalocele, 4 fetuses with gastrochisis and 3
fetuses showing features of meconium peritonitis.
|
GIT
anomalies
|
No.
of fetuses affected
|
Percentage
|
|
Esophageal
atresia
|
26
|
3.73
|
|
Duodenal
atresia
|
13
|
1.52
|
|
Intestinal
atresia
|
12
|
1.40
|
|
Diaphragmatic
hernia
|
25
|
2.92
|
|
Omphalocele
|
08
|
0.93
|
|
Gastrochisis
|
05
|
0.47
|
|
Meconium
peritonitis
|
03
|
0.35
|
