Crossmatching Maternal and Fetal Blood in Sheep

Abstract

We investigated the incidence of ex vivo incompatibility between ovine maternal RBC and fetal plasma. Time-mated singleton pregnant ewes (n = 8) underwent cesarean delivery of the fetus; at the time of delivery, paired maternal and fetal blood samples were collected and subsequently separated for storage as packed RBC and fresh frozen plasma. Gel column crossmatching was performed 3 to 4 wk later. All fetus-dam crossmatches were considered major crossmatches, combining fetal (recipient) plasma with dam (donor) RBC. The plasma of 8 fetuses was cross-matched with RBC from 5 dams; all autologous controls were negative, and all but one crossmatch (1 of 40, 2.5%) were considered compatible. In addition, the plasma of 3 dams was crossmatched with RBC from 5 dams; all autologous controls were negative; however, significant incompatibility was noted. In total, 4 of 13 (30.8%) dam-dam crossmatches were considered incompatible. The results of this initial study suggest that when a single animal receives multiple blood-product transfusions, the risk of an immunologic transfusion reaction can be reduced by ensuring that the blood products are obtained from a single donor, performing a crossmatch prior to transfusion, and the use of synthetic products to increase the oxygen carrying capacity of fetal blood.

Maternal-fetal Blood Major Crossmatching in Merino Sheep

“…A score of 1+ was given if RBCs were seen in the bottom half of the gel, 2+ if RBCs were seen throughout the entire gel, 3+ if RBCs were seen in the top half of the gel, and 4+ if all RBCs were evident in a tight disc at the top of the gel. Consistent with literature in dogs 2 and with our previous study, 7 crossmatches were interpreted as compatible or negative, if less than or equal to 1+, and incompatible or positive if greater than or equal to 2+. Compatibility reactions were evaluated by a single experienced investigator (CRS).…”

“…The incidence of incompatibility reactions between dams in this study was low as compared with previous studies, which reported a frequency of incompatibility from 16% to 30.8%. 4,7,10 The size and structure of these studies varied, with 12 male Merino sheep in a prospective study, 10 58 small ruminants in a retrospective clinical case series 4 and 8 Merino ewes in the most recent prospective study. 7 This variation in sample size, breed of sheep and methodology complicates meaningful comparison the results.…”

“…Preliminary investigation of ex vivo incompatibility between ovine maternal red blood cells (RBCs) and fetal plasma was performed and reported an incidence of dam-dam and maternal (dam)-fetal incompatibility as 30.8% and 2.5% respectively. 7 The motivation for the preliminary investigation was the need for blood transfusions to preterm lambs housed in the context of an 'artificial placenta' or ex vivo uterine environment (EVE). 5,6,8,11 This EVE is a sheep model of an artificial version of extracorporeal support for a human fetus.…”

“…The preliminary investigation had various limitations: a relatively small sample size; concern that the duration of storage of samples before cross matching may have overestimated the frequency of incompatibility reactions; and the collection of samples from only naïve fetuses, prior to any transfusions being administered. 7 The current study addresses these limitations, providing additional data to inform the decision-making process for administration of blood and blood products to preterm fetuses in the EVE model.…”

“…All gel column crossmatches were performed according to the manufacturer's instructions ("Gel", BioRad ID-Cards, NaCl, Enzyme Test and Cold Agglutinins DiaMed GmbH, Cressier, Switzerland) as described previously. 7 Briefly, 10 uL of packed RBCs from each donor was added to a tube with 1 mL of low ionic strength solution (LISS, ID-Diluent 2, DiaMed), and mixed gently, to prepare a 1% RBC suspension. For each donor-recipient combination, 50 μL of the 1% donor RBC suspension and 25 μL of recipient plasma were added on top of the gel in successive card microtubes (6 microtubes per card) and incubated at 37 °C for 15 min in an incubator (Thermoline Scientific Refrigerated Incubator, Smithfield, New South Wales).…”