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NEURAL TUBE DEFECTS DIAGNOSIS
Category: Child Health
Abstract : DIAGNOSTIC DETECTION OF NTDS AND ASSOCIATED NEUROLOGIC LESIONS Presence of
open NTDs can be detected with the measurement of AFP in the amniotic fluid or
maternal bloodstream. AFP is the major serum protein in early embryonic life and
is 90% of the total serum globulin in a fetus. It is believed to be involved in
preventing fetal immune rejection and is first made in the yolk sac and th
DIAGNOSTIC DETECTION OF NTDS AND ASSOCIATED NEUROLOGIC LESIONS
Presence of
open NTDs can be detected with the measurement of AFP in the amniotic fluid or
maternal bloodstream. AFP is the major serum protein in early embryonic life and
is 90% of the total serum globulin in a fetus.
It is believed to be involved in
preventing fetal immune rejection and is first made in the yolk sac and then
later in the gastrointestinal system and liver of the fetus. It goes from the
fetal blood stream to the fetal urinary tract, where it is excreted into the
maternal amniotic fluid. The AFP also can leak into the amniotic fluid from open
NTDs such as anencephaly and myelomeningocele in which the fetal blood stream is
in contact with the amniotic fluid.
The first step in prenatal screening
is drawing the maternal AFP between 15 and 20 weeks of gestation. A
patient-specific risk then is calculated based on gestational age and AFP level.
Normal AFP concentration in the maternal serum is usually lower than 500 ng/mL.
Determining precise gestational age is essential because fetal AFP levels are
age specific and can peak in a normal fetus at 12-15 weeks of gestation. For
example, at 20 weeks' gestation, a maternal serum AFP concentration higher than
1,000 ng/mL would be indicative of an open NTD. The measurement of maternal
serum AFP levels is more than 75% accurate in detecting an open NTD at more than
15 weeks of gestation. In patients in whom a question persists, amniotic AFP can
be obtained. It is a significantly more accurate test, especially at 15-20
weeks' gestation, and detects approximately 98% of all open NTDs, although this
method is not the preferred screening test. Amniotic fluid acetylcholinesterase
levels add an increased degree of resolution.
Detection of an NTD with
fetal ultrasound in the hands of a skilled ultrasonographer usually is 98%
specific. False-positive findings can result from multiple pregnancies or
inaccurate fetal dating. However, closed NTDs also can sometimes remain
undetected, especially in cases of skin-covered lipomyelomeningoceles and
meningoceles, in which the AFP also may be normal. These closed NTDs comprise
about 10% or more of total NTDs discovered. A skilled ultrasonographer can
detect these lesions with almost 95% sensitivity.
A partial list of the
fetal anomalies that are associated with an elevated AFP is as follows (neural
tube defects diagnosis):
• Anencephaly
• Spina bifida cystica
•
Encephalocele (leaking)
• Conjoined twins
• Omphalocele
• Turner
syndrome
• Gastroschisis
• Extrophy of the cloaca
•
Oligohydramniosis
• Sacrococcygeal teratoma
• Polycystic kidneys
•
Fetal death
• Urinary tract obstruction
If the parents decide not to
terminate a pregnancy in which the fetus is affected with an NTD, extensive
counseling takes place. Parents are educated on optimal prenatal care and
expectations once a child is born. If diagnosed early enough, a discussion of
fetal surgery is warranted. Currently, this option is available at only 2 major
centers: Vanderbilt Medical Center and University of Pennsylvania. Although this
approach has not been proven scientifically advantageous, preliminary evidence
suggests that this experimental approach has promise in decreasing resultant
neurologic problems in the neonate. Long-term outcome data are currently
lacking.
If conventional delivery is chosen, the study by Shurtleff and
his colleagues is important to note. Infants with NTD who were exposed to labor
and vaginal delivery were more than 2 times more likely to have severe paralysis
or motor deterioration than those delivered by cesarean section without labor.
Although this remains a controversial point, most centers such as that of the
author recommend a cesarean section prior to labor in mothers carrying a fetus
with a myelomeningocele.
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