Читать книгу Genetic Disorders and the Fetus - Группа авторов - Страница 130

For most laboratories today, reports are completed in 6–14 days with a mean of 7–11 days to the final report, and the rate of culture failure is below 1 percent, depending somewhat on the timing of the amniocentesis,⁶⁶⁰ and in many laboratories averages closer to 0.1–0.2 percent (van Dyke, unpublished data). There are multiple reasons for cell culture problems and outright failure.⁶⁶¹ With the increased experience of the obstetrician and the universal use of high‐resolution ultrasound, maternal urine is now rarely received as an AF sample. Anecdotal evidence of some labs suggests that the risk of culture failure is higher in cases of fetal aneuploidy. In one published retrospective study, 56 (0.7 percent) of 7,872 AF samples did not grow.⁶⁶² Twenty‐four of these were judged technically inadequate and 10 were from women whose fetuses had died. Of the remaining 32 cases, 4 had proven (determined by repeat amniocentesis) and 4 had possible (extrapolated from fetal phenotype) aneuploidy. This 25 percent rate of growth failure associated with proven or likely chromosomal aberrations was not confirmed in a similar study comprising 6,369 cases and a growth failure rate of 1.2 percent.⁶⁶³ A study of 14,615 cases identified a higher incidence of culture failure in advanced pregnancies with abnormal ultrasound findings but no association with aneuploidy.⁶⁶⁴ In addition to a baseline level of less than 1 percent unexplained culture failure (the standard set by the American College of Medical Genetics is 2 percent),^{623, 624, 665} a number of known hazards can interfere with cell growth.