12.3 HDFN Treatment and Prevention
Key Takeaways
- IUT red cells are usually group O, antigen-negative for the maternal antibody, irradiated, CMV-safe, HbS-negative, packed to a high hematocrit, and crossmatched against maternal plasma.
- After birth, phototherapy isomerizes bilirubin, IVIG slows further hemolysis, and exchange transfusion removes bilirubin plus coated cells plus residual antibody.
- RhIG is Rh immune globulin — use the generic name, not WinRho or Rhophylac as if they were a different class. Routine U.S. doses are 300 µg at 28 weeks and again within 72 hours postpartum if the infant is D-pos.
- One 300 µg vial covers 30 mL whole blood (15 mL RBC). Additional vials = (KB% × maternal blood volume) / 30, then round up and add 1. MICRhoGAM 50 µg is an early-pregnancy dose in some protocols, not the term dose.
- After antenatal RhIG the screen can show passive anti-D and the mother can type as weak D from circulating fetal cells — do not call her D-pos and do not withhold postpartum RhIG.
12.3 HDFN Treatment and Prevention
Quick Answer: Intrauterine transfusion (IUT) uses group O, antigen-negative, irradiated, CMV-safe, HbS-negative red cells, packed to a high hematocrit, and crossmatched against maternal plasma. After birth: phototherapy, IVIG, and exchange transfusion (removes bilirubin and coated cells). RhIG is Rh immune globulin (not a brand name). Give 300 µg at 28 weeks and again within 72 hours postpartum if the infant is D-pos; give extra vials after a large FMH. One 300 µg vial covers 30 mL whole blood / 15 mL RBC. Vials = (KB% × maternal blood volume) / 30, round up, add 1. After RhIG, a mother may look weak D — do not call her D-pos. MICRhoGAM 50 µg is an early-pregnancy dose in some protocols, not the term dose.
III.B.3 finishes with what you issue and what you inject. The exam loves unit attributes and RhIG math. Brand names are a distraction. Calculate the bleed, irradiate the IUT, and never withhold postpartum RhIG just because the 28-week dose made the screen positive.
Intrauterine transfusion
When MCA-PSV is ≥1.5 MoM, the fetus is hydropic, or PUBS shows a critically low hematocrit, the fetus needs red cells before birth. Access is usually the umbilical vein.
The unit is built for a tiny, immunocompromised, CMV-naive recipient who must not receive a large volume:
- ABO/Rh: usually group O, D-neg (or D type compatible with mother and fetus), and negative for the antigen the mother has antibody against. If she has anti-K, the unit is K-neg even if you are also matching D.
- Crossmatch against maternal plasma (or an adsorbed maternal sample). The fetus is swimming in her IgG. Do not crossmatch to the father.
- Hematocrit high — typically about 75–85% — so you deliver oxygen-carrying cells without volume-overloading the fetus. Additive supernatant is removed or minimized.
- Irradiated — required. The fetus cannot reject donor lymphocytes. TA-GVHD is the nightmare.
- CMV-safe — leukoreduced (CMV-reduced-risk) and/or CMV-seronegative, per institutional policy. Both is common for IUT.
- HbS-negative — a hypoxic fetus must not receive AS trait cells that can sickle.
- Relatively fresh (often ≤5–7 days) for 2,3-DPG and lower supernatant potassium.
- Antigen-matched beyond the implicated antibody when feasible (at least K-neg for a female fetus) so you do not create a new alloantibody during the IUT series.
IUT treats anemia. It does not treat bilirubin — the placenta is still doing that. After several IUTs the infant may type as the donor (group O, DAT weaker) because most circulating cells are transfused. That is expected, not a typing error.
Phototherapy, IVIG, and exchange
Once the cord is cut, bilirubin is your problem.
Phototherapy uses blue light (~460–490 nm) to convert unconjugated bilirubin to water-soluble isomers (lumirubin) that can be excreted without conjugation. It is first-line for neonatal hyperbilirubinemia, including ABO HDFN.
IVIG (typically 0.5–1 g/kg) occupies Fc receptors and reduces further extravascular hemolysis. It is used when bilirubin is rising through phototherapy and you are trying to avoid exchange. It does not remove bilirubin already in plasma.
Exchange transfusion is the definitive wash-out:
- Removes unconjugated bilirubin.
- Removes IgG-coated red cells.
- Removes residual maternal antibody.
- Replaces with antigen-negative cells that will survive.
A double-volume exchange replaces most of the infant’s red-cell mass. The product is usually reconstituted whole blood: antigen-negative, group-O or ABO-compatible with both mother and infant red cells plus AB or group-compatible plasma, hematocrit ~45–60%, irradiated, CMV-safe, HbS-neg, crossmatched to maternal plasma, relatively fresh. Aliquot from a fresh irradiated red-cell unit; do not grab yesterday’s unirradiated O-neg off the trauma shelf and call it an exchange unit.
RhIG: what it is and when it goes in
Rh immune globulin is concentrated anti-D IgG. U.S. products are polyclonal (from immunized D-neg donors). Some countries have monoclonal anti-D. On the exam, write Rh immune globulin (RhIG). RhoGAM, MICRhoGAM, HyperRHO, Rhophylac, and WinRho SDF are brand names for the same class. WinRho is also labeled for D-pos ITP — that is a different indication and can hemolyze D+ patients. Do not import ITP dosing into an HDFN stem.
RhIG prevents immunization. It does not treat HDFN that is already underway, and it does nothing if the woman already has immune anti-D. If the antibody is immune, skip RhIG and manage the fetus.
Routine U.S. schedule for a D-neg woman without immune anti-D:
- Antepartum: 300 µg at 26–28 weeks (commonly spoken as 28 weeks).
- Postpartum: another 300 µg within 72 hours if the infant is D-pos or weak D+. If the 72-hour window is missed, still give it as soon as you realize.
- If the infant is D-neg (and not weak D), no postpartum dose.
Additional doses after potentially sensitizing events: amniocentesis, CVS, cordocentesis, external version, abdominal trauma, antepartum bleeding, ectopic, miscarriage, abortion, stillbirth, molar pregnancy. Before 12 weeks, some protocols use 50 µg (MICRhoGAM / mini-dose) because the fetal red-cell mass is tiny. After 12 weeks, and for all routine 28-week and term doses, use 300 µg. Mini-dose is not a term postpartum dose.
One 300 µg (1,500 IU) vial covers 30 mL of D+ whole blood, which is about 15 mL of packed red cells. A 50 µg mini-dose covers about 2.5 mL whole blood. A negative rosette means you are inside that 30 mL envelope. A positive rosette means you must measure.
Worked RhIG calculation
Formula this chapter uses:
- Fetal whole-blood volume (mL) = (KB% / 100) × maternal blood volume
- Vials of 300 µg = fetal whole-blood volume / 30
- Round up to the next whole vial, then add 1 extra vial.
Maternal blood volume is taken as 5,000 mL unless the stem gives you a weight-based volume. The 50-shortcut is the same math: KB% × 50 = mL fetal whole blood when volume is 5,000 mL, because 1% of 5,000 mL is 50 mL.
Example 1. Kleihauer–Betke = 1.8%. Volume not stated, so use 5,000 mL.
- Fetal whole blood = 0.018 × 5,000 = 90 mL
- 90 / 30 = 3.0 vials to cover the measured bleed
- Already a whole number: still add 1 → issue 4 vials of 300 µg RhIG
Example 2. KB = 2.4%.
- 0.024 × 5,000 = 120 mL
- 120 / 30 = 4.0 → add 1 → 5 vials
Example 3, with a remainder. KB = 1.3%.
- 0.013 × 5,000 = 65 mL
- 65 / 30 = 2.17 → round up to 3, add 1 → 4 vials
Some AABB-style stems use a decimal rule instead of always rounding up: if the calculated value’s first decimal is <5, keep the whole number then add 1; if ≥5, go up one whole number then add 1. For 2.17 that rule yields 2 + 1 = 3 — one vial fewer than “always round up, then add 1.” If the stem cites AABB Technical Manual rounding, use the decimal rule. If the stem says round up and add one, do exactly that. Write the arithmetic so you can see which instruction you followed.
Give the extra vials IM or IV per product label (Rhophylac and WinRho can be IV; traditional RhoGAM is IM). When the calculated IM volume is huge, IV products are kinder. The drug is still Rh immune globulin.
Passive anti-D is not immune anti-D, and she is not D-pos
After the 28-week dose, the postpartum screen will often show anti-D. That is passive RhIG. It is usually a low titer (≤4, sometimes 8) and it does not rise. Still give the postpartum dose if the infant is D-pos. Passive anti-D is not a reason to withhold RhIG and not a reason to start MCA-PSV.
Immune anti-D appears without recent RhIG, or the titer is high or rising weeks after a dose should have faded. That woman needs HDFN management, not another vial.
Antepartum or delivery sample can type as weak D or mixed-field D+ after a large FMH (D+ fetal cells in a D-neg mother) and, with some IV RhIG situations, serologic noise. Do not relabel the mother D-positive. She remains a D-neg candidate for RhIG. Quantify the bleed and dose her. Calling her D-pos is how you skip RhIG on the exact patient who needs the most vials.
| Product / fact | Teaching number | Use it for |
|---|---|---|
| Standard U.S. RhIG vial | 300 µg (1,500 IU) | 28 weeks, postpartum, most FMH events after 12 weeks |
| Coverage of one 300 µg vial | 30 mL whole blood / 15 mL RBC | One vial if rosette negative |
| Mini-dose (MICRhoGAM) | 50 µg | Some early-pregnancy protocols only |
| Mini-dose coverage | ~2.5 mL whole blood | Not a term postpartum dose |
| Calculation | (KB% × maternal BV) / 30, round up, +1 | Positive rosette / known large FMH |
| Names on the exam | Rh immune globulin | WinRho, Rhophylac, RhoGAM are brands, not a different class |
Exam traps
- Issuing an IUT that is not irradiated, or that is HbS-untested, or that is crossmatched to the father.
- Withholding postpartum RhIG because the antibody screen is positive after the 28-week dose.
- Using 50 µg for a term delivery.
- Forgetting to add the extra vial after you divide by 30.
- Calling the mother D-pos because delivery typing looks weakly D+.
- Giving RhIG to a woman who already has immune anti-D.
- Treating WinRho / Rhophylac as a different drug class. They are Rh immune globulin.
Which red-cell unit is appropriate for intrauterine transfusion to a fetus whose mother has anti-D?
A Kleihauer–Betke is 1.8% in a D-neg postpartum patient. Maternal blood volume is not stated. Using (KB% × 5,000 mL) / 30, then rounding up and adding 1, how many 300 µg RhIG vials do you issue?
A D-neg woman received 300 µg of RhIG at 28 weeks. At delivery the infant is D-pos, the maternal screen shows anti-D, and the mother’s D type now looks weakly positive. What is the correct action?