The Principles of Clinical Cytogenetics - Extra Materials - Springer

272 Linda Marie Randolph
Table 4
The Incidence Of De Novo Balanced Structural Rearrangements
in 337,357 Genetic Amniocenteses
De novo rearrangement No. of cases Percentage
Reciprocal translocation 176 0.047
Robertsonian translocation 42 0.011
Inversion 33 0.009
Supernumerary small marker chromosome 162 0.040
Satellited marker 77 0.020
Nonsatellited marker 85 0.023
Total 413 0.109
Source: Data from ref. 36.
three studies of stillbirths and neonatal deaths, of those in which chromosome analysis was performed,
52 of 823 (6.3%) studied had a chromosome abnormality. Of these 823, 59 macerated stillbirths
were studied, of which 7 (11.9%) had a chromosome abnormality. Of 215 nonmacerated
stillborns, 9 (4.2%) were chromosomally abnormal, and of 549 neonatal deaths, 33 (6.0%) had a
chromosome abnormality (30). Given the value it provides families in terms of understanding more
about their losses and in providing recurrence risks, it is recommended that consideration of chromosome
analysis be given in all such cases (see Table 7).
PRENATAL CYTOGENETIC DIAGNOSIS
Genetic Amniocentesis
With increased public awareness, number of practitioners, laboratory capacity, proportion of
women older than 35 having babies, and use of maternal serum screening, the utilization rate of
amniocentesis has grown. It was estimated that in 1974, 3000 women underwent genetic amniocentesis
(40), and the number now is in the millions. The increased utilization has extended to women of
lower socioeconomic status who previously did not have access to or finances for the procedure (41).
With improvements in laboratory procedures, including sterile technique, plasticware, enriched cell
culture media, and automated harvesting and imaging systems, the turnaround time for reporting
results of an amniocentesis has dropped dramatically, from several weeks in the 1970s and 1980s to
less than 1 week in some laboratories today. The cost of the laboratory test has dropped as well due to
increased efficiency and competition. Thus, prenatal diagnosis by amniocentesis has become and
probably will remain, by far, the most common mode of prenatal diagnosis until such time as a
reliable, cost-effective noninvasive procedure is developed.
The accuracy of amniocentesis for the detection of recognized chromosome abnormalities is
greater than 99%. Diagnostic accuracy has been enhanced by the recent use of fluorescence in situ
hybridization (FISH) and chromosome-specific probes. These are of particular value in marker chromosome,
translocation, and deletion cases, when microscopic findings require further study for clarification
(42–49) (see Chapter 17).
Conventional Amniocentesis—15–24 Weeks of Gestation
Mid-trimester, defined here as the 15th through the 24th week of gestation, is, by far, the most
common time period for performing the amniocentesis procedure. Culture of amniotic fluid cells is optimal
in this time period (50,51), both from the perspective of rapidity of cell growth (and therefore sample
turnaround time) and because the culture failure rate is less than 0.5% in experienced laboratories.
The risks associated with mid-trimester amniocentesis include leakage of fluid, cramping, bleeding,
infection, and miscarriage. The risk of miscarriage following mid-trimester amniocentesis is