Rh status and the pregnant trauma patient

Reading Time: 4 minutes
Shona Jain
Shona Jain

MS2 Rutgers New Jersey Medical School, NJ

Kavita Jain
Kavita Jain

PG4 Department of Obstetrics and Gynecology, Mercer University, Macon, GA

Rh doesn’t just stand for Restoration Hardware…

The Pre-brief

A 27-year-old female arrives in your ED after a motor vehicle collision. She was the restrained driver in a head on collision. She states she is 13 weeks pregnant and this is her first pregnancy. She denies loss of consciousness and is complaining of abdominal pain. You ask her about her Rh status and she looks back at you like you have 3 heads. 

Does she have?

A) a traumatic brain injury and cannot answer questions

B) she is G1P0 and has not been educated on this yet. 

C) you actually have 3 heads since it was just halloween and you forget to take your costume off.

What is Rh-D alloimmunization? ← the technical term for the phenomenon

Rh-D is one of more than 30 antigens that can be present on the surface of red blood cells. Another familiar group of red blood cell antigens include the ABO family. 

The rh-D antigen is especially significant in pregnancy. Alloimmunization occurs when the immune system attacks foreign antigens that are distinct from antigens on individual’s cells. Specifically mixing of maternal and fetal blood (maternal-fetal hemorrhage) in any trimester can cause maternal formation of antibodies against fetal rh-D.

What does it do and why is it a problem if you’re pregnant?

The significance of Rh  alloimmunization comes into play when Rh+ and Rh-  blood mix. This happens most often in pregnancy. If a mother is Rh- and is carrying an Rh+ fetus, and the mother has pre-existing Anti Rh antibodies, there is potential for the mother’s anti-Rh antibodies to attack the fetus’s red blood cells. This immune attack is one of the few causes of hemolytic disease of the newborn, and can be fatal to the fetus. The fetus can present at birth with kernicterus, jaundice, or in severe cases, hydrops fetalis. The patient population that experiences hemolytic disease of the newborn are Rh- mother’s who have been pregnant before with an Rh+ fetus. During pregnancy, or most commonly during delivery, the blood of the mother and fetus come in contact; another common cause of maternal-fetal hemorrhage is trauma.

How do you address it? 

The way to allow an Rh- mother to have a viable pregnancy with a Rh+ fetus is to administer RhoGAM. RhoGAM is an intramuscular injection of anti-D immune globulin. A dose of 300 micrograms can prevent alloimmunization after exposure to up to 30 mL of fetal blood. The mode of action is not completely understood, but it is thought that the administration of the passive antibodies prevents the mother’s immune system from creating them, and thus there is not an attack on the fetus’s Rh+ red blood cells. RhoGAM is given to pregnant Rh- women in a number of situations that involve the mixing of maternal and fetal blood. Some instances are listed as follows:

  • Maternal or fetal bleeding during pregnancy (trauma) –>maternal fetal hemorrhage
  • 72 hours following delivery of an Rh+ baby
  • During routine prenatal Rh immunization at 26-28 weeks of pregnancy if fetus is Rh+
  • Ectopic pregnancy
  • Actual or threatened pregnancy loss at any stage
  • If father’s Rh status is not known and this is maternal bleeding

There is conflicting evidence as to the recommendation of when to administer Rhogam to non trauma pregnant patients. (Some guidelines say significant maternal bleeding before 12 weeks of gestation requires RhoGAM, while other sources say to wait until after 12 weeks of gestation to administer RhoGAM. There is no official guideline at this time).  Consistently, evidence supports administration of RhoGaM for all Rh- trauma patients.

Risk/adverse reaction of RhoGaM:

RhoGaM is ultimately a blood product manufactured from pooled plasma selected for high titers of IgG antibodies to D-positive erythrocytes. There are actually very few risks of administration. 

Possible reactions to administration include hypersensitivity reaction, anaphylaxis, injection site reactions. There is a very rare chance that could get an infection such as HIV or hepatitis, although there are no actual reports of this. 

*RhoGAM should not be administered to a patient who is Rh positive. This will yield the same results as administering someone the wrong blood type. 

Kleihauer Betke Test

The Kleihauer Betke Test (KB) test measures the percentage of fetal red blood cells in the maternal circulation from recent fetal-maternal hemorrhage.    Any result other than 0 is considered positive with a threshold of 5mL. It can also be used to predict the risk of preterm labor after maternal trauma and should therefore not be limited to only Rh- patients. 

Kleihauer test, showing fetal red blood cells in rose-pink color, while adult red blood cells are only seen as "ghosts". Source: Wikimedia Commons

Fun Fact: The reason blood type O has its name is because originally, the scientist wrote zero to signify the lack of surface antigens on the blood type. It was read incorrectly as “O,” and thus blood type O was born.

The Debrief

  • Give rhogam to any/all Rh negative pregnant trauma patients
  • Updating tetanus is safe in pregnant patients – should be administered at 28 weeks in every pregnancy
  • The KB test can be utilized in all pregnant trauma patients


  1. Jain V, Chari R, Maslovitz S, Farine D, Bujold E, et al. Guidelines for the management of a pregnant trauma patient. Maternal Fetal Medicine Committee. J Obstet Gynaecol Can 2015;37:553-74. (Level III)
  2. Practice Bulletin No. 181: Prevention of Rh D Alloimmunization. Obstet Gynecol. 2017;130(2):e57-e70. doi:10.1097/AOG.0000000000002232.
  3. Muench MV, Baschat AA, Reddy UM, Mighty HE, Weiner CP, Scalea TM, Harman CR. Kleihauer-betke testing is important in all cases of maternal trauma. J Trauma. 2004 Nov;57(5):1094-8. doi: 10.1097/01.ta.0000096654.37009.b7. PMID: 15580038.
  4. Pollack W, Ascar WQ, Crispen JF, O’Connor RR, Ho TY. Studies on Rh prophylaxis. II Rh immune prophylaxis after transfusion with Rh- positive blood. Transfusions 1971; 11:340-44.
  5. KLEIHAUER E, BRAUN H, BETKE K. [Demonstration of fetal hemoglobin in erythrocytes of a blood smear]. Klin Wochenschr. 1957 Jun 15;35(12):637-8.
  6. Pelikan DM, Mesker WE, Scherjon SA, Kanhai HH, Tanke HJ. Improvement of the Kleihauer-Betke test by automated detection of fetal erythrocytes in maternal blood. Cytometry B Clin Cytom. 2003 Jul;54(1):1-9.
  7. http://www.rhogam.com/index.php. Updated: April, 2019. Accessed: November 8, 2020. 
  8. Farhud DD, Zarif Yeganeh M. A brief history of human blood groups. Iran J Public Health. 2013;42(1):1-6.


More Posts

Related Posts

Would love your thoughts, please comment.x