Protocols for High-Risk Pregnancies. Группа авторов
and fetal tumors, but because these indications are so rare, none of them has sufficient data to show that fetal transfusion leads to improved outcomes.
Procedure‐related risks
Over the last 15 years, reported survival rates for intrauterine fetal transfusion for red cell alloimmunization have improved to over 90% in expert hands. Survival rates for parvovirus infection are lower, in the 70–80% range, likely related to late diagnosis in many cases. In the largest series to date of fetal intravascular transfusion, procedure‐related complications have decreased over time, from 9.8% to 3.3% per fetus. The two most common complications of fetal transfusion in this series were fetal demise and fetal distress leading to emergency cesarean delivery. Fetal distress may occur due to cord trauma or volume overload related to the procedure itself. Delayed complications include chorioamnionitis, premature rupture of membranes, and preterm labor but these are extremely rare. Needling of a free loop of cord, inadvertent arterial puncture, and failure to use fetal paralysis are all associated with higher rates of procedural complications. Nonetheless, procedure‐related fetal demise decreased over time in this large series of 1678 transfusions, from 1.6% to 0.6% per procedure. Associated risk factors for fetal loss include presence of fetal hydrops, early gestational age at first transfusion, and limited operator experience.
Long‐term effects
There is evidence to suggest long‐lasting effects of fetal anemia seen in survivors of fetal blood transfusion. Studies done in these patients and in their nonanemic siblings show that the subjects who underwent transfusion were born at earlier gestation, and as adults have smaller left ventricular volumes, increased left ventricular wall thickness, and decreased myocardial perfusion at rest. This is important information that shows that cardiovascular development is altered in fetuses who survive anemia, which may have implications for adult cardiovascular health. Reassuringly, neurodevelopmental outcomes appear to be good, and at least one large study of over 1284 fetal transfusions performed in 451 fetuses in a 20‐year period showed that over 95% of the survivors had normal neurodevelopment.
Technique
Fetal blood sampling
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.
Fetal blood transfusion
Though diagnostic cordocentesis may be done in the outpatient setting, most fetal transfusions are performed in or near an operating room, particularly if a fetus is viable and a failed procedure might prompt delivery. The patient would be evaluated preoperatively by the obstetric anesthesia providers, as well as the NICU team, depending on gestational age. Anesthesia options for the mother range from regional block to sedation and local anesthetic. The NICU team will want to discuss with the patient the neonatal management of anemia in a newborn. Steroids for fetal lung maturation should also be considered preprocedurally depending on gestational age, though they are not used routinely in some major centers.
It is a critical part of preparation for fetal blood transfusion to communicate with your blood bank/transfusion services, so they are aware of the request for a specially prepared unit. These units require a maternal “type and cross” for ½ to 1 unit of O negative, washed, leukoreduced, irradiated, cytomegalovirus (CMV)‐negative packed red blood cells (PRBC), with a hematocrit (Hct) of at least 75%. If there is suspicion of fetal thrombocytopenia (for instance, in cases of parvovirus) you may also need to order an aliquot of platelets for fetal transfusion.
Preoperative testing of the mother should include complete blood count (CBC). You will need the maternal MCV to compare to the fetal MCV to ensure you have sampled the fetal blood, since fetal RBCs are larger than maternal RBCs. Labs to be drawn at the time of fetal blood sampling (fetal Hgb/Hct, MCV, blood type/Rh, and platelets) should be preordered in the medical record so results are processed in the most expeditious manner, since total transfusion volume will depend on those initial results.
In anticipation of the fetal transfusion, you will want to make all calculations for transfusion volume ahead of time based on most recent estimated fetal weight. The original formula described by Rodeck and colleagues in 1984 is:
Estimated fetal blood volume varies with gestational age but a good rule of thumb is 100 mL per kg. A helpful webpage for quicker calculations is www.perinatology.com/protocols/rhc.htm. As an example, assuming a Hct of 75% for the transfusion unit, and a 1600 g fetus with a starting Hct of 20% and an end Hct goal of 35%, you will need to transfuse 35 mL of blood. You will want to have worked out the possibilities for several starting hematocrits and chart them on a table so you don’t have to do math in your head while holding a needle inside the cord of a fetus!
Generally, you might suspect a low Hct hematocrit based on sonographic findings (hydrops, for example) or other signs of fetal compromise. The goal at the first transfusion in such cases is to reach a closing Hct of 30–35%. Overtransfusion might put the fetus at risk of heart failure. The compromised fetus might need follow‐up transfusion within a week of the initial one with a goal of closing Hct 40–45%. Thereafter transfusions are scheduled depending on the diagnosis and severity of disease.
The preferred route of fetal transfusion is intravascular, via the umbilical vein. On occasion, related to fetal position or posterior placenta, it might be technically impossible to access the umbilical vein at the cord, making it necessary to access the intrahepatic portion of the umbilical vein. In the very premature or hydropic fetus, intraperitoneal transfusion may also be performed by injecting donor blood directly into the fetal peritoneal cavity, where blood would be absorbed through lymphatics. Absorption of the transfused blood may not be optimal in these situations.
A typical set‐up for fetal transfusion is shown in Figure 9.2. Your OR table should be readied with prepared syringes with paralytics and sedative for the fetus. The appropriate