THE DISAPPEARANCE OF FETAL AND DONOR RED-BLOOD-CELLS IN ALLOIMMUNIZEDPREGNANCIES - A REAPPRAISAL

Objective To determine the proportional reduction per day in the numbe r of fetal and donor red blood cells from the fetal circulation after intrauterine intravascular transfusions. Design A retrospective study of 302 transfusions in 101 fetuses. Setting The Department of Obstetri cs and Gynaecology of the University Medical Centre Leiden, The Nether lands. Methods We measured the haematocrit in fetal samples both befor e and after repeated intravascular intrauterine transfusion in fetuses with alloimmune disease. The percentage of fetal erythrocytes was det ermined in Kleihauer-Betke stained smears. The decline of fetal, donor and mixed red blood cells was calculated by dividing the proportional decrease of the haematocrit values by the number of days between tran sfusions, also after correction for changes in fetoplacental volumes. Results (given as mean [SD]) are derived from the proportional changes of haematocrit per day. Results The interval between the first and se cond transfusion (15.5 days [SD 5.2]) was shorter than between subsequ ent transfusions (means ranging from 21.4 to 21.9 days; P less than or equal to 0.0001). The decline per day of mixed, and of donor red bloo d cells, calculated without corrections for volume changes did not dif fer from those corrected for volume changes resulting from the transfu sion and from fetal growth (correction factor 1.1 [SD 0.4]). Since the coefficient of variance is smaller for the uncorrected decline values , this type of calculation is preferable for clinical purposes. The di sappearance of fetal erythrocytes after the first transfusion (6.1%/da y [SD 2.9]) was faster than that of mixed fetal and donor red blood ce lls (3.2%/day [SD 1.2]; P < 0.0001) and of donor cells alone (1.4%/day [SD 1.6]; P < 0.0001). The decline of the mixed red blood cell popula tion became the same as that of the donor cells (2.2%/day [SD 0.8]) af ter the second transfusion. This decline of donor cells was higher tha n after the first transfusion (1.4%/day [SD 1.6]; P < 0.05). After the first transfusion the fetal erythrocytes disappeared faster after tra nsplacental puncture of the umbilical cord (6.6%/day [SD 2.8]) than af ter transamniotic punctures (5.4%/day [SD 2.7]; P = 0.05). The mixed r ed blood cell also decreased faster (3.5%/day [SD 1.3] versus 2.8%/day [SD 0.9]; P < 0.01). Conclusion The fast disappearance of fetal eryth rocytes, especially after transplacental punctures, shows that the int erval between the first and second transfusion needs to be shorter tha n that for intervals between subsequent transfusions. The number of do nor erythrocytes declines by approximately 2% per day.