Vaginal spotting is not uncommon following transcervical sampling, but it is self-limited and not associated with pregnancy loss. The incidence of infection is less than 0.5 percent (American College of Obstetricians and Gynecologists, 20 16c).
A limitation of CVS is that chromosomal mosaicism is identified in up to 2 percent of specimens (Malvestiti, 2015). In most cases, the mosaicism reflects confined placental mosaicism rather than a true second cell line within the fetus. his is discussed in Chapter 13 (p. 263). Amniocentesis should be ofered, and if the result is normal, the mosaicism is usually presumed to be confined to the placenta. Conined placental mosaicism has been associated with growth-restricted newborns (Bafero, 2012).
his procedure is also called cordocentesis or percutaneous umbilical blood sampling (PUBS). It was initially described for fetal transfusion of red blood cells in the setting of anemia from alloimmunization, and fetal anemia assessment remains the most common indication (Chap. 16, p. 304). Fetal blood sampling is also performed for assessment and treatment of platelet alloimmunization and for fetal karyotype determination, particularly in cases of mosaicism identified following amniocentesis or CVS. Fetal blood karyotyping can be accomplished within 24 to 48 hours. Thus, it is significantly quicker than the 7-to 10-day turnaround time with amniocentesis or CVS. Although fetal blood can be analyzed for virtually any test performed on neonatal blood, improvements in tests available with amniocentesis and CVS have eliminated the need for fetal venipuncture in most cases (Society for Maternal-Fetal Medicine, 2013).
FIGURE 14-6 Oromandibular limb hypogenesis is characterized by transverse limb deficiency and absence or hypoplasia of the tongue or mandible. This is hypothesized to result from vascular disruption with subsequent loss of tissue. A. Sonogram obtained at 25 weeks' gestation demonstrates a fetal limb reduction defect involving the right hand.
B. Photograph of the right extremity of the same newborn. Chorionic villus sampling was not performed in this pregnancy. (Used with permission from Dr. Jamie Morgan.)
Under direct sonographic guidance, using aseptic technique, the operator introduces a 22-or 23-gauge spinal needle into the umbilical vein, and blood is slowly withdrawn into a heparinized syringe (Fig. 14-7). Adequate visualization of the needle is essential. 5 with amniocentesis, a longer needle may be required depending on patient habitus. Fetal blood sampling is often performed near the placental cord insertion site, where it may be easier to enter the cord if the placenta lies anteriorly. Alternatively, a free loop of cord may be punctured. Because fetal blood sampling requires more time than other fetal procedures, a local anesthetic may be administered. Prophylactic antibiotics are used at some centers, although no trils support this policy. Arterial puncture is avoided, because it may result in vasospasm and fetal bradycardia. ter the needle is removed, fetal cardiac motion is documented, and the site is observed for bleeding.
he procedure-related fetal loss rate following fetal blood sampling approximates 1.4 percent (Ghidini, 1993; Tongsong, 2001). The actual loss rate varies according to the procedure indication and the fetal status. Other complications may include cord vessel bleeding in 20 to 30 percent of cases, fetal-maternal bleeding in approximately 40 percent of cases in which the placenta is traversed, and fetal bradycardia in 5 to 10 percent (Boupaijit, 2012; Society for Maternal-Fetal Medicine,