FIGURE 14-7 Fetal blood sampling. A. Access to the umbilical vein varies depending on placental location and cord position. With an anterior placenta, the needle may traverse the placenta. Inset: With posterior placentation, the needle passes through amnionic fiuid before penetrating the umbilical vein. Alternatively, a free loop of cord may be accessed. B. Sonogram shows an anterior placenta with transplacental needle passage into the umbilical vein (U). (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, 201/.) 2013). Most complications are transitory, with complete recovery, but some result in fetal loss.
In one series of more than 2000 procedures comparing fetal blood sampling near the placental cord insertion site with puncture of a free loop, rates of procedure success, pregnancy loss, visible bleeding from the cord, and fetal bradycardia did not difer. Time to complete the procedure was signiicantly shorter if the cord was sampled at the placental insertion site than in a free 100p-5 versus 7 minutes. However, sampling at the insertion site had a higher rate of maternal blood contamination (T angshewinsirikul, 2011).
For couples undergoing in vitro fertilization (IVF), genetic testing performed on oocytes or embryos before implantation may provide valuable information regarding the chromosomal complement and single-gene disorders. There are two separate categories of testing-preimplantation genetic diagnosis (PGD) and preimplantation genetic screening (PGS)-each with diferent indications. Comprehensive genetic counseling is required before consideration of these procedures. There are three techniques that are used for both categories: 1.
Polar body anaysis is a technique used to infer whether a developing oocyte is afected by a maternally inherited genetic disorder. The irst and second polar bodies are normally extruded from the developing oocyte following meiosis I and II, and their sampling should not afect fetal development. However, two separate micromanipulation procedures are required, and genetic abnormalities of paternal origin are not detected. his technique has been used to diagnose 146 mendelian disorders, and the reported accuracy exceeds 99 percent (Kuliev, 2011).
2.
Blastomere biopsy is done at the 6-to 8-cell (cleavage) stage when an embryo is 3 days old. his allows both maternal and paternal genomes to be evaluated. One cell is typically removed through a hole made in the zona pellucida (Fig. 14-8). A limitation of using this technique for aneuploidy assessment is that because of mitotic nondisjunction, mosaicism of the blastomeres may not reflect the chromosomal complement of the developing embryo (American Society for Reproductive Medicine, 2008). In addition, the implantation rate of normal embryos is slightly lower following this technique.
FIGURE 14-8 Blastomere biopsy. After a blastomere is selected, it is then drawn into the pipette. (Reproduced with permission from Doody J: Treatment of the infertile couple. Hoffman BL, Schorge JO, Bradshaw KD, et al (eds): Williams Gynecology, 3rd ed. New York, McGraw-Hili Education, 2016.) 3. Trophectoderm biopsy involves removal of 5 to 7 cells from a 5-to 6-day blastocyst. An advantage is that because the trophectoderm cells give rise to the trophoblast-the placenta-no cells are removed from the developing embryo. Disadvantageously, because the procedure is performed later in development, if genetic analysis cannot be performed rapidly, then cryopreservation and embryo transfer during a later IVF cycle may be required.