Читать книгу Protocols for High-Risk Pregnancies - Группа авторов - Страница 98

Fetal blood sampling can be done in the outpatient setting and requires minimal preparation, especially in a previable pregnancy. As shown in Figure 9.1, a sterile field, a 22 gauge needle, heparinized syringes, and ultrasound guidance are typically all that is required for diagnostic cordocentesis. Color Doppler can help to identify umbilical cord vessels at their insertion into the placenta. Accessing the fetal umbilical vein at its placental insertion is preferred; this is the most stable point and the least likely to allow the needle to dislodge. When this approach is technically difficult, the second choice should be the intrahepatic part of the umbilical vein. Alternatively, a free loop of cord can be used, which will prove more challenging and is also associated with a higher procedural loss rate. Placement into the lumen of the umbilical vein is immediately confirmed by observing either backflow of blood or turbulent flow in the cord when a saline flush is utilized and further documented by assessing putative fetal versus known maternal red blood cell (RBC) mean corpuscular volume (MCV) values. Fetal samples are drawn into heparinized syringes and sent for testing. Some streaming is expected from the cord once the needle is withdrawn.

Figure 9.1 A typical procedure tray set‐up for cordocentesis, with 22 gauge spinal needles of varying lengths, 10 cc and 20 cc syringes to collect amniotic fluid samples, if needed, and heparinized syringes to collect a fetal blood sample. Sterile gel and ultrasound transducer probe cover are also shown in the image.