Early amniocentesis is associated with signiicantly higher rates of procedure-related complications than other fetal procedures. hese include development of talipes equinovarus (clubfoot), amnionic luid leakage, and fetal loss (Canadian Early and MidTrimester Amniocentesis Trial, 1998; Philip, 2004). Given these risks, the American College of Obstetricians and Gynecologists (20 16b) recommends that early amniocentesis not be performed.
Biopsy of chorionic villi is typically performed between 10 and 13 weeks' gestation. As with amniocentesis, the specimen is generally sent for karyotyping or CMA. The primary advantage of villus biopsy is that results are available earlier in pregnancy, permitting more time for decision-making and safer pregnancy termination, if desired. Very few analyses speciically require either amnionic luid or placental tissue.
Chorionic villi may be obtained transcervically or transabdominally, using aseptic technique. Both approaches are considered equally safe and efective (American College of Obstetricians and Gynecologists, 2016b). Transcervical CVS is performed using a specifically designed catheter made from lexible polyethylene that contains a blunt-tipped, malleable stylet. Transabdominal sampling is performed using an 18-or 20-gauge spinal needle. With either technique, transabdominal sonography is used to guide the catheter or needle into the early placentachorion rondosum, followed by aspiration of villi into a syringe containing tissue culture media (Fig. 14-5).
FIGURE 14-5 A. Transcervical chorionic villus sampling. B. Catheter entering the placenta is marked and labeled. (Reproduced with permission from Mastrobattista JM, Espinoza J: Invasive prenatal diagnostic procedures. In Yeomans ER, Hoffman BL, Gilstrap LC III, et al (eds): Cunningham and Gilstrap's Operative Obstetrics, 3rd ed. New York, McGraw-Hili Education, 201o7.)
Relative contraindications include vaginal bleeding or spotting, active genital tract infection, extreme uterine ante-or retrolexion, or body habitus precluding adequate visualization. If the patient ish D-negative and unsensitized, anti-D immune globulin is administered following the procedure.
he overal loss rate following CVS is higher than that following midtrimester amniocentesis. This is because of background spontaneous losses, that is, losses that would have occurred between the first and second trimester in the absence of a fetal procedure. he procedurerelated fetal loss rate is comparable with that of amniocentesis. Caughey and colleagues (2006) found that the overall loss rate following CVS was approximately 2 percent compared with less than 1 percent following amniocentesis. However, the adjusted procedure-related loss rate approximated 1 per 400 for either procedure. The indication for CVS will also afect the loss rate. For example, fetuses with increased NT thickness have a greater likelihood of demise. Finally, there is a learning curve associated with safe performance of CVS (Silver, 1990; Wijnberger, 2003).
An early problem with CVS was its association with limbreduction dects and oro mandibular limb hypogenesis, shown in Figre 14-6 (Firth, 1991, 1994; Hsieh, 1995). hese were subsequently found to be associated with procedures performed at 7 weeks' gestation (Holmes, 1993). When performed at : 10 weeks' gestation, the incidence of limb defects does not exceed the background population rate of about 1 per 1000 (Evans, 2005; Kuliev, 1996).