Amniocentesis

Nineteen women underwent amniocentesis for the determination of fetal sex. Several different X-llnked abnormalities constituted the Indications for this procedure, and these Included hemophilia A, hemophilia B, Duchenne muscular dystrophy, optic albinism, X-llnked mental retardation, the Lesch-Nyhan syndrome (due to dlflclency of hypoxanthlne-guanlne phosphorlbosyltransferase, and Fabry s disease (due to deficiency of an a-galact-osldase). Fourteen of the fetuses were male. Including one which turned out to be a set of twins, and most of the male pregnancies were terminated. The sex determination being carried out for Fabry s disease Is of particular Interest, since In this case It was desired to find out whether the fetus was a female. 

The monitoring of pregnancies for neural tube defects Is the most recent of the Indications for prenatal diagnosis In families In which one child has been affected, the risk of recurrence Is approximately 4% Of the 16 pregnancies In which amniocentesis was done to determine the level of a-fetoprotein, no affected fetuses were found ... 

In these 500 cases, there were 26 culture failures, an Incidence of about 5% Nine women of this group underwent a second aminocentesls, and successful cultures were obtained The other 17, or 3 4% of the total, did not obtain any results, either because of spontaneous abortions prior to the time a second amniocentesis could be performed (In four) or because the family elected not to proceed There were no Instances of severe or significant fetal Injury, although small linear "scars" were noted on four fetuses Three fetuses had abnormalities which were not related to the procedure Itself, Including spina bifida, osteogenesis Imperfecta, and congenital heart disease ... 

One set of undetected triplets also occurred. In addition to the twins already mentioned Ten abortions occurred following amniocentesis, three occurring within one week of the procedure and associated with fever, and seven not associated with fever and occurring between 18 and 50 days after amniocentesis Itself, the former group which comprises 0 4% of the total, must be considered a direct complication However, even this conclusion must be tempered by the fact that In the week prior to a scheduled amniocentesis, 20 women had spontaneous abortions ... 

Hoehn, H Bryant, E M. Karp, L E and Martin, 6. M "Cultivated Cells from Diagnostic Amniocentesis In Second Trimester Pregnancies I Clinical Morphology and Growth Potential". Pedlat Res., (1974),, 746-754. 

Nadler, H. L. and Gerbie, A. B. "Role of Amniocentesis in the Intrauterine Detection of Genetic Disorders". 

RDIg may be used after abortion, miscarriage, amniocentesis, or abdominal trauma. 

A man with sickle cell disease and his phenotypically normal wife request genetic testing because they are concerned about the risk for their unborn child. DNA samples from the man and the woman and from fetal cells obtained by amniocentesis are analyzed using the PCR to amplify exon 1 of the p-globin gene. 

A couple is expecting their first child and have consulted a genetic coun or because the woman had a brother who died of sickle cell anemia. There is also a history of disease in the man s family. Fetal cells are obtained by amniocentesis. Which test would best determine whether the fetus would be born with the disease ... 

Answer D. DNA-based test would have to be used on the ceils obtained from amniocentesis. They would not express the p-globin gene. 

The increased risk of trisomy with advanced maternal age motivates more than half of pregnant women in North America to undergo prenatal diagnosis (most commonly, amniocentesis or chorionic villus sampling, discussed in Oiapter 6). Down syndrome can also be screened by assaying maternal serum levels of a-fetoprotein, chorionic gonadotropin, and unconjugated estriol. This so-called triple screen can detect approximately 70% of fetuses with Down syndrome. 

A small sample of amniotic fluid (10-20 ml) is collected at approximately 16 weeks gestation. Fetal cells are present in the amniotic fluid and can be used to diagnose single-gene disorders, chromosome abnormalities, and some biochemical disorders. Elevated a-fetoprotein levels indicate a fetus with a neural tube defect. The risk of fetal demise because of amniocentesis is estimated to be approximately 1/200. 

Amniocentesis conducted between 15 and 21 weeks gestation yields cells capable of growth in culture. These can be easily used to extract DNA (or RNA) and subjected to analysis. This tissue is less subject to concern with maternal cell contamination than CVS, but it can still present diagnostic problems, such as confined placental mosaicism. The level of such problems can sometimes be assessed using... 

The specimen will be the basis for the analytic analysis. Is it RNA or DNA What is the origin of the tissue Amniocentesis Was it a spontaneous product of conception Were anatomic pathology slides or tissue blocks prepared Are cell lines involved Are these primary or immortalized Was a chorionic villus sampling procedure done Is the sample properly collected peripheral blood The answers to each of these questions should be noted, and considered part of the validation of a useful nucleic acid extraction method. A molecular diagnostics laboratory should adhere to the highest standards in providing services, and prior validation of applicable nucleic acid extraction procedures is a must to ensure high-quality service. 

P4. Pauker, S. R, and Pauker, S. G., The amniocentesis decision Ten years of decision analytic experience. Birth Defects Orig. Artie. Ser. 23(2), 151-169 (1987). 

Adults Prophylaxis after delivery, abortion, amniocentesis 300 meg IM within 72 hours. Massive transplacental haemorrhage 25 mcg/ml of foetal erythrocytes. 

If the patient is exposed to VPA or CBZ, the presence of neural tube defects should be evaluated (e.g., serum alpha protein, amniocentesis, ultrasound), especially if they are used together. 

Fibroblasts are typically grown from a small skin biopsy sample collected during an outpatient visit or as part of a planned surgical procedure following routine culturing techniques. Cell cultures may also be derived from umbilical cord or, for prenatal diagnostic purposes, from amniocytes obtained by amniocentesis. In our laboratory the analysis for each patient is performed in triplicate. 

Nadel, A.S.. et al. Absence of Needs for Amniocentesis in Patients with Elevated Levels of Maternal Serum Alpha-Fetoprotein and Normal Ultrasonographic Examinations, N. Eng. J. Med., 557 (August 30, 1990). 

---