Clinical Scenario: 26 yo F G1P0 at 33 weeks pregnancy presents via ambulance after a MVC. She was a seatbelted driver with airbags deployed, no intrusion into her compartment. She’s complaining of abdominal pain. On exam, she has a seatbelt sign and very mild vaginal bleeding. While placing your orders, you wonder if there are any lab tests that you should order specifically in a pregnant trauma patient. You also wonder if you should go ahead and order her RhIG while you’re on the computer…
Question: Who do you give RhIG to? How much do you give? How much time do you have from injury to give it? What labs do you order?
Rho(D) immune globulin (RhIG, aka Rhogam) is given to Rh negative females for concerns of isoimmunization during fetomaternal hemorrhage (there’s a break in placental barrier and fetal Rh positive blood enters maternal circulation). As little as 0.01-0.03mL of fetal blood can cause isoimmunization.
A type and screen is needed initially to determine the Rh status of the patient. A Rh negative female should receive an initial prophylactic RhIG dose of 300mcg IM within 72 hours of injury. This dose protects against 30mL of fetal blood. However, depending on the amount of fetomaternal hemorrhage, the patient may need more RhIG. To determine this, a Kleihauer Betke test should be ordered to quantify the degree of fetomaternal hemorrhage (A blood sample from the female is drawn and placed in an acid-elution assay and stained. The fetal RBCs are left on the smear as rose pink while the maternal cells turn “ghost-like”). The percent fetal cells is resulted and the additional number of vials of RhIG needed can be further calculated (check out this link for an example). The Kleihauer Betke test has a threshold of 5mL to be positive, so even if it is negative, it does not mean there was no fetomaternal hemorrhage. **Do not underdose RhIG**
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