Testing for fetal maternal hemorrhage using a post-partum blood sample collected 1-2 hours versus 12-24 hours after delivery

A transfusion medicine physician in Seattle reports that she recently sent a letter to obstetricians stating that in regards to postnatal testing of Rh negative mothers, a post-partum sample to detect fetal-maternal bleeding should be collected from the patient within 1-2 hours post-partum, as recommended in the Practice guidelines for prenatal and perinatal immunohematology, revisited. Editors' note: The exact wording of the recommendation in the aforementioned practice guideline is as follows "... a maternal sample should be obtained approximately 1 hour after delivery and tested for evidence of an FMH in excess of 30 mL of fetal blood." The Seattle colleague continues saying that many of the obstetricians have responded to her letter with feedback that it is an unrealistic expectation to collect the requested blood sample so soon after delivery. She wonders if anyone can tell her why a sample drawn 12-24 hours post-partum would not be sufficient for the purpose of detecting fetal red cells in the maternal circulation.

The following responses have been received.

ADDENDA Nov. 2, 2008

1. Dr. Melanie Kennedy, Director of Transfusion Medicine at Ohio State University Medical Center (attribution used with permission) comments in response to the inquiry from the physician in Seattle about the 1 hour postpartem sample for fetal screen. According to Dr. Kennedy, the recommendation to collect a post-partum sample for determination of the volume of fetal-maternal bleed within about one hour was to avoid underestimating the true volume of bleeding, since a major ABO incompatibility between mother and infant may cause rapid clearance of incompatible fetal cells in the maternal circulation and falsely low estimates of fetal-maternal hemorrhage. In addition, a 1-hour wait allows adequate mixing of the fetal cells with the mother's. The 1-hour recommendation first appeared in the 12th edition (1996) of the AABB Technical Manual without a reference. The recommendation was also made by Judd: Practice guidelines for prenatal and perinatal immunohematology, revisited. Transfusion 2001;41:1445-1452 without citation.
   
   
2. According to John Judd, Emeritus Professor of the Department of Pathology at the University of Michigan (attribution used with permission), the testing of a recently delivered mother to detect and quantify a fetal-maternal bleed is largely an administrative issue. According to Professor Judd, the AABB SSCC group that drafted the original guidelines back in the early 1990's felt that there should be a stipulated time when the sample was drawn (so that the testing did not get forgotten) and 1 hour post delivery was selected arbitrarily. Since the timing was arbitrary, Professor Judd feels confident that a delay of 12-24 hours to collect the sample would be safe, if a 1-2 hour timing is impractical.

ADDENDA Nov. 3, 2008

3. A medical technologist in Indiana reports that his reading of the kit used at his institution for detection of fetal maternal bleeding says that it is best to wait at least one hour after delivery to collect a maternal sample Researching the citations, he was unable to find a source for this, nor did he find any published study comparing alloimmunization rates when a maternal sample was collected 1-2 hrs vs 12-24 hrs after the birth of the baby. He can think of two possibile answers for this recommendation. First, in the ABO-incompatible mother, fetal cells are cleared more quickly, possibly leading to a false-negative fetal-maternal bleed screen. From available evidence, he is not convinced yet that these quickly-destroyed fetal cells will cause higher rates of alloimmunization if they are not detected. Second, articles dealing with inadvertent exposure of Rh positive red cells in the Rh negative individual suggest giving RhIg as soon as possible after the exposure. Taking birth as the exposure, testing ASAP (with the extention that RhIg will be given ASAP also) will reduce the chance that the mother's immune system will respond to the D antigen before the RhIg is injected. Finally, he vaguely remembers that the 72-hr rule for giving post-partum RhIg was an arbitrary decision. He is not aware of any published study suggesting that alloimmunizatuion to the D-antigen is decreased if RhIg is given within a shorter timeframe. After discussions with their OB department and understanding that their small facility has only one night tech, they decided to continue their current practice of drawing the fetal-maternal screen sample with the next morning's CBC and to issue RhIg (if indicated) later that day. Cord blood is tested STAT to determine the Rh type, and RhIg is almost always injected within 36 hrs of delivery.

ADDENDA Nov. 11, 2008

4. After reading the responses from Dr. Kennedy and Professor Judd, a colleague in Indiana is surprised that the recommendation of when to collect a post-partum maternal sample for detection of fetal maternal bleeding is so arbitrary. She hopes that data will be forthcoming to prove that it is truly important to collect the maternal sample within 1-2 hours after a baby's birth, or to show that it makes no difference if there is a delay of up to 24 hours to collect the post-partum maternal blood sample.

ADDENDA Nov. 23, 2008

5. Dr. J. Lawrence Naiman, retired pediatric hematologist and co-editor of Oski and Naiman's "Hematologic Problems of the Newborn" (WB Saunders, Philadelphia. 1966, 1972 & 1982), and Emeritus Clinical Professor of Pediatrics and Pathology at Stanford University School of Medicine (attribution used with permission), comments that in regard to the timing of RhIg administration, a citation from an OB GYN Forum, although not quite resolving the question of 1 vs 24 hours, offers another (less scientific) explanation. It pertains to the experiences of Dr Vince Freda and colleagues during their original studies of the efficacy of RhIg: "It seems that the original RhoGam studies were done in Rh negative prison volunteers at Sing Sing prison in New York (Freda was at Columbia University in Manhattan). They wanted to give the volunteers IV infusions of various quantities of Rh positive blood and then come back the next day and give them their primitive Rh immune globulin preparation. The warden, however, would not allow them to do that, apparently because of prison security considerations. Therefore, they reasoned, what would happen in a small hospital with a small blood bank that was not well staffed on the weekends and a patient delivered on Friday afternoon. Could they wait until Monday to do the work-up and give the Rh immune globulin to the patient. They asked the prison warden if it would be possible for them to come back in three days (72 hours) after the blood transfusion to see the prisoners, The warden said that would be OK."

ADDENDA Dec. 15, 2008

6. A colleague in Georgia reports that their labor and delivery (L&D) nurses screen for Rh Negative mothers delivering and order the Fetal Screen usually within an hour after delivery. The cord bloods are sent to Blood Bank after delivery; the techs review the label comments to get the mother’s blood type. If they see the mother is Rh Negative, then they will call L&D to order the Fetal Screen if one has not been ordered. The fetal screen sample is drawn >90% of the time between 1-4 hours post-delivery. The testing is done on first shift the next morning for inpatient routine deliveries, other shifts if indicated by circumstances surrounding Rh Immune Globulin orders. The system reportedly has worked well for many years because everyone helps check each other. They give around 250 doses of Rh Immune Globulin each year. Their personal comment is that there seems to be a lot more emphasis being placed on Rh Immune Globulin administration or fetal screening in articles and discussions that would lead one to believe that we have a tremendous problem. However, they do not recall seeing the statistics that bear this out. In their experience, they cannot recall any patients who h

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