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medical-site.info: Obstetrics and Gynecology: An Illustrated Colour Text great selection of similar New, Used and Collectible Books available now at great prices. Title: Obstetrics and Gynecology: An Illustrated Publisher: Churchill Livingstone . Publication Date: Binding: Paperback. Book Condition: New. Edition: 1. Obstetrics and Gynecology book. Read reviews from world's largest community for readers. A highly illustrated, short, atlas-style text of.
Routine karyotyping does take up to 3 weeks because of the need to culture cells first. Screening for open neural tube defects is also carried out by measuring the maternal serum AFP at 16 weeks.
Nuchal translucency Screening for aneuploidy is also possible by measuring the fetal nuchal thickness on first trimester ultrasound. The overall survival for Fig. Both these tests are screening tests for chromosomal problems. This allows selection of a group of mothers who can then be considered for an invasive diagnostic test.
Methods of obtaining tissue Chorionic villus sampling CVS Samples of mesenchymal cells of the chorionic villi are obtained for chromosomal and DNA analysis. The transabdominal technique is now more favoured, as the transcervical technique may give a higher infection and fetal loss rate. Chorionic villus sampling is performed at weeks' gestation.
A needle is introduced through the maternal abdomen under ultrasound guidance, into the placenta and along the chorionic plate. A sample of the villi Fig. Cells from the direct preparation allow preliminary karyotype and DNA analysis within 24 hours, but this is usually confirmed with a cultured preparation as well.
Chorionic villus sampling only rarely leads to erroneous results, due to placental mosaicism placental tissue of different cell lines can be identified from one placenta, e. XO, XX but errors from this can be virtually eliminated providing decisions are deferred until both the direct and culture results are available. Karyotypic discrepancy between fetus and placenta increases with increasing gestation and if rapid results are required over 20 weeks fetal blood sampling or amniocentesis with FISH is preferable see below.
The advantage of chorionic villus sampling is that there is no breach of the amniotic cavity and that it allows an early diagnosis with the option of a suction termination of pregnancy.
There is, however, good evidence to suggest that psychological parental morbidity is independent of whether a diagnosis is made in the first or second trimester and indeed medical termination of pregnancy may carry less psychological morbidity than surgical even if medical complications are higher.
Amniocentesis Amniocentesis involves withdrawing a sample of amniotic fluid containing fetal cells by passing a needle using direct ultrasound control through the maternal abdomen Fig. A karyotype of the fetal cells is obtained see above. Amniocentesis performed in the presence of a raised maternal AFP level appears to be associated with a significant increase in miscarriage rates.
Cordocentesis This technique may be used later in pregnancy when a rapid result is required. Often this will be at a later gestation after an ultrasound scan has shown an anomaly that is strongly associated with a genetic defect.
A needle is introduced transabdominally into the umbilical artery or vein. The most stable portion of the cord suitable for this is at the point of insertion.
The blood sample obtained can be used for karyotyping and for the diagnosis of other conditions such as haemoglobinopathies, viral infections and metabolic disorders. The disadvantage of cordocentesis is that it requires a highly skilled operator.
Complications include fetal haemorrhage, cord haematoma and fetal bradycardia. Diagnostic tests for chromosome abnormality Karyotyping Human chromosomes can be examined directly in rapidly dividing tissue.
However it is more usual to culture cells and then use colchicine to inhibit the formation of the spindle and arrest cell division at metaphase which allows the preparations that we are familiar with Fig.
Chromosomes can then be paired according to their size, position of the centromere, and the Giemsa stain this shows a characteristic banding pattern for each chromosome allowing individual identification.
DNA analysis In an increasing number of inherited diseases it is now possible to identify a single gene defect or omission that is responsible. Fetal cells obtained by the various sampling techniques are cultured and their chromosomal DNA separated. This DNA is digested with restriction enzymes.
The resulting fragments are separated by Southern blotting. A radioisotope-labelled DNA probe is then added and autoradiography allows identification of any hybridization.
Specific probes are available for sickle cell disease, thalassaemia, and cystic fibrosis. Fluorescent in situ hybridization FISH In situ hybridization permits the analysis of genetic material of a single nucleus, by incubating a fixed dried cell with a specific probe, which binds to the gene of interest Fig.
The use of a fluorescent marker tagged to the gene probe leads to the acronym FISH. This technique is sensitive enough to demonstrate each allele on individual chromatids but is not yet reliable enough for single cell analysis so is applied to larger samples.
It provides a rapid diagnosis of trisomy, triploidy or sex chromosome problems if appropriate markers are used.
Fetal chromosomal abnormality Screening tests for genetic abnormality include nuchal translucency measurement, maternal serum screening and ultrasound examination of the fetus. Screening tests will not detect all abnormalities.
Diagnostic tests are usually used after an abnormal screening test and include chorionic villus sampling, amniocentesis and cordocentesis. Amniocentesis is associated with the lowest fetal loss rate. This remains true even when the potential risks are small; for example being recalled with an abnormal level of a-fetoprotein AFP , or with the finding of a choroid plexus cyst on routine ultrasound scan. The very greatest of care should be taken in explaining any findings to parents.
Tact, understanding and reassurance if appropriate are paramount. The advice given to parents is of such importance that it will frequently be necessary to involve senior members of the obstetrics team as well as members of other specialties, particularly paediatricians, clinical geneticists and radiologists. The aims of prenatal diagnosis are fourfold: the identification at an early gestation of abnormalities incompatible with survival, or likely to result in severe handicap, in order to prepare parents and offer the option of termination of pregnancy the identification of conditions which may influence the timing, site or mode of delivery the identification of fetuses who would benefit from early paediatric intervention the identification of fetuses who may benefit from in utero treatment rare.
It should not be assumed that all parents are going to request termination of pregnancy even in the presence of lethal abnormality. Many couples have opted to continue pregnancies in the face of severe defects that have resulted in either intrauterine or early neonatal death, and have expressed the view that they found it easier to cope with grief having held their child.
Others say that they were glad of the opportunity to terminate the pregnancy at an early stage and that they could not have coped with going on. More controversial still are the problems of chronic diseases with long-term handicap and long-term suffering for both the child and its parents. The parents themselves must decide what action they wish to take - it is they who will have to live with the consequences.
It is our role to advise, guide and respect their final wishes, irrespective of our own personal views. Screening for fetal abnormalities Structural anomalies are best seen on ultrasound scan and many clinicians advocate that all mothers should be offered at least one detailed ultrasound at around weeks or earlier. This has the advantage that previously unsuspected major or lethal anomalies e.
Furthermore, problems may be uncovered; for example one of the 'soft markers' see below , the natural history of which is uncertain. This may generate unnecessary anxiety and increase the number of invasive diagnostic procedures and thereby the loss rate in otherwise healthy pregnancies.
Chromosomal abnormalities are much more difficult to identify on scan. While around two-thirds of fetuses with Down's syndrome will look normal at 18 weeks, most with Edwards' or Patau's syndrome do show some abnormality, even though these are often not specific or diagnostic.
In the absence of routine ultrasound scans, it is possible to screen for open neural tube defects by measuring the maternal serum AFP at 16 weeks.
AFP is an alpha-globulin of similar molecular weight to albumin, which is synthesized by the fetal liver. Any break in the integrity of the fetus allows the AFP to escape into the maternal circulation and therefore be elevated on serum testing.
Those with levels greater than 2. Raised levels are also found following first trimester bleeding, or with intrauterine death fetal autolysis , abdominal wall defects, or multiple pregnancy Fig. Even if the scan is normal, raised AFP is still a marker for later pre-eclampsia or intrauterine growth restriction. Aneuploidy soft markers These are structural features found on ultrasound scan which in themselves are not a problem, but which may be pointers to chromosomal problems.
Examples include choroid plexus cysts, mild renal pelvic dilatation, an echogenic focus Fig. If isolated, the risk of chromosomal problems is low, but if more than one is found, or if there are any other structural defects, the risk is very much higher.
Congenital heart disease This is the commonest congenital malformation in children and affects about live births. The four-chamber view of the heart can be used as a screening test Fig.
In addition, viewing the aorta and pulmonary artery increases Fetal abnormality Fig. The aorta [a] overrides the interventricular septum s. This may be occipital or frontal. Isolated meningoceles carry a good prognosis, whereas those with microcephaly secondary to brain herniation carry a very poor prognosis.
Spina bifida Fig. In a meningocele, dura and arachnoid mater bulge through the defect, whereas in a myelomeningocele, the central canal of the cord is exposed. Those with myelomeningoceles usually have abnormal lower limb neurology and many have hydrocephalus. In addition to immobility and mental retardation, there may be problems with urinary tract infection UTI , bladder dysfunction, bowel dysfunction, and social and sexual isolation.
There is good evidence that the overall incidence has fallen over the past 15 years independently of any screening programmes. Daily folic acid taken from before conception reduces the recurrence risk of neural tube defects in those who have had a previously affected child. There is an increased incidence of recurrence in subsequent pregnancies. At 18 weeks most of the major connections can be seen, but high-risk pregnancies e. This may contain both intestines and liver.
There is also an association with ectopia vesicae and ectopia cardia midline bladder and cardiac hernias. If the exomphalos is isolated i. The sac rarely ruptures at vaginal delivery. Gastroschisis Fig. Small bowel without a peritoneal covering protrudes and floats free in the peritoneal fluid.
Gut dilatation may be associated with bowel obstruction or ischaemia but is not directly linked to prognosis. These babies are usually small for dates and require very close surveillance. Neural tube defects The neural tube is formed from the closing of the neural folds, with both anterior and posterior neuropores closed by 6 weeks' gestation Fig.
Failure of closure of the anterior neuropore results in anencephaly or an encephalocele, and failure of posterior closure in spina bifida. The skull vault and cerebral cortex are absent The infant is either stillborn or, if liveborn, will usually die shortly after birth although some may survive for several days.
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