Читать книгу Protocols for High-Risk Pregnancies - Группа авторов - Страница 44

Prenatal diagnostic testing can be performed on fetal tissue collected by first‐trimester CVS or second‐trimester amniocentesis. CVS is typically performed between 10 and 14 weeks of gestation, although a later placental biopsy is also possible and may be required under some clinical circumstances. Two approaches are commonly used to access the placenta under sonographic guidance; with the transabdominal approach, a 20 gauge spinal needle traverses the maternal abdominal and uterine walls, while with the transcervical approach, a plastic cannula or biopsy forceps traverses the vagina and cervix. Both transabdominal and transcervical CVS are associated with an overall pregnancy loss rate of approximately 1 in 455 or 0.22%; this is not statistically different from the risk associated with amniocentesis. CVS performed prior to 10 weeks of gestation has been associated with a risk of fetal limb reduction defects and is not recommended; this risk is not increased with later procedures (10 weeks and later).

Genetic amniocentesis is most commonly performed between 15 and 20 weeks of gestation, although can also be performed later. Sonographically directed placement of a 22 gauge spinal needle into the amniotic cavity is a very safe procedure, with a reported loss rate of 1 in 900 pregnancies, or 0.11%. Recent data indicate that when compared to patients with the same risk profile, the loss rate of CVS and amniocentesis is negligible.

Fetal tissue obtained with CVS or amniocentesis can be cultured for karyotype analysis, or DNA can be extracted from chorionic villi, amniotic fluid, or cultured fetal cells for chromosomal microarray analysis (CMA) or other specialized genetic testing. When indicated, fluorescence in situ hybridization can be done on interphase cells for rapid aneuploidy testing or on metaphase cells for identification of microdeletions or duplications.