Substance + claimed effects

Rh incompatibility in pregnancy refers to the immunological mismatch between a pregnant person who lacks the RhD antigen on their red blood cells (RhD-negative) and a fetus who inherits RhD from the biological father (RhD-positive). When fetal red cells cross into maternal circulation — at delivery, with bleeding, with trauma, or after instrumented obstetric events — the mother can form anti-D IgG antibodies. Those antibodies cross the placenta in any subsequent RhD-positive pregnancy and destroy fetal red cells, producing hemolytic disease of the fetus and newborn (HDFN): fetal anemia, hydrops fetalis, stillbirth, neonatal hyperbilirubinemia, and kernicterus de Haas et al. 2015. The intervention covered here is the modern management package: a first-trimester antibody screen, paternal/fetal RhD typing where applicable, antenatal anti-D immune globulin (RhIG) at 28 weeks, postpartum RhIG within 72 hours of an RhD-positive birth, and additional RhIG after any sensitizing event (miscarriage, ectopic, amniocentesis, abdominal trauma, external cephalic version). Claimed consequences: near-elimination of new alloimmunization, prevention of fetal/newborn anemia and jaundice in current and future pregnancies, prevention of stillbirth and neonatal mortality from HDFN, and — for already-immunized pregnancies — monitoring via middle-cerebral-artery Doppler with intrauterine transfusion as rescue therapy ACOG 2017 Moise 2021.

Evidence by addressing question

Mechanism

The RhD antigen is a transmembrane protein on red blood cells encoded by the RHD gene; absence of a functional RHD gene produces the RhD-negative phenotype, present in roughly 15% of people of European ancestry, 3–8% of African ancestry, and under 1% of East Asian ancestry. When even small volumes of fetal RhD-positive blood enter maternal circulation — most often during the third stage of labor, but also during miscarriage, ectopic pregnancy, amniocentesis, chorionic villus sampling, external cephalic version, abdominal trauma, or any antepartum bleeding — the maternal immune system can mount a primary alloimmune response, producing low-titer IgM first and then high-titer IgG anti-D over weeks to months. In a subsequent pregnancy, that anti-D IgG readily crosses the placenta (active transport via the neonatal Fc receptor), binds RhD-positive fetal erythrocytes, and triggers extravascular hemolysis in the fetal spleen. The downstream cascade: fetal anemia, compensatory extramedullary erythropoiesis, hepatosplenomegaly, high-output cardiac failure, hydrops fetalis (skin edema, ascites, pleural and pericardial effusions), and stillbirth. After birth, hemolysis continues from circulating maternal antibody; the unconjugated bilirubin load overwhelms the neonate's still-immature glucuronidation, producing severe jaundice and, untreated, kernicterus (bilirubin deposition in basal ganglia and brainstem, producing permanent cerebral palsy, deafness, and movement disorders) de Haas et al. 2015 Moise 2021.

Anti-D immune globulin works by passive antibody-mediated immune suppression. Administered exogenous polyclonal anti-D IgG binds fetal RhD-positive cells in maternal circulation, marking them for rapid clearance in the maternal spleen before resident antigen-presenting cells can prime a primary T-cell-dependent B-cell response against RhD. The molecular details of why passive IgG suppresses an active alloresponse to the same antigen — antigen masking, epitope blocking, FcγRIIB-mediated B-cell inhibition, central deletion of D-specific clones — are still debated, but the empirical effect is unambiguous: pre-emptive saturation of fetal D-positive cells in maternal circulation prevents the durable memory response that would otherwise threaten every later RhD-positive pregnancy Bowman 1988 de Haas et al. 2015.

Evidence

The efficacy of anti-D prophylaxis is one of the more decisive results in 20th-century obstetrics. Before any prophylaxis, the alloimmunization rate among RhD-negative women delivering an RhD-positive ABO-compatible infant was roughly 13–16% within six months of delivery Bowman 1988 ACOG 2017. The seminal clinical trials of Freda, Gorman, and Pollack in the 1960s — culminating in FDA licensure of RhoGAM in 1968 — demonstrated that a single intramuscular dose of anti-D IgG given within 72 hours of delivery cut the postpartum sensitization rate to roughly 1–2%, an order-of-magnitude reduction Pollack et al. 1968. Adding routine antepartum prophylaxis at 28 weeks (introduced in the early 1980s) further drove the residual rate to roughly 0.1–0.2% — and most of the remaining failures trace to silent third-trimester fetomaternal hemorrhage or missed doses, not to ineffective drug ACOG 2017 Crowther et al. 2013. The 2013 Cochrane review of anti-D prophylaxis in pregnancy (two trials, ~4500 women) confirmed a statistically significant reduction in alloimmunization at delivery and at 12 months postpartum, with a number needed to treat in the dozens for direct prevention but cascading benefit across every subsequent pregnancy the woman has Crowther et al. 2013.

Outcome data after the prophylaxis era are equally striking. Where anti-D coverage is universal — most high-income countries since the late 1970s — Rh disease has gone from a major obstetric killer (one of the top causes of neonatal death in mid-20th-century cohorts) to a clinical rarity. Where coverage is patchy or absent — much of South Asia, sub-Saharan Africa, parts of Eastern Europe — Rh disease still causes an estimated 160,000 perinatal deaths and 100,000 cases of disability annually, with regional kernicterus rates of 25–38 per 100,000 livebirths Bhutani et al. 2013 Pegoraro et al. 2020. About half of women worldwide who need RhIG do not receive it.

For already-immunized pregnancies, the monitoring and rescue stack has its own decisive trial base. Mari et al.'s 2000 NEJM study established that middle-cerebral-artery peak systolic velocity (MCA-PSV) above 1.5 multiples of the median (MoM) detects moderate-to-severe fetal anemia with sensitivity approaching 100%, replacing serial amniocentesis as the standard for surveillance Mari et al. 2000. Intrauterine intravascular transfusion — pioneered by Liley in 1963 using intraperitoneal injection guided by paper-clip landmarks on plain X-ray — now achieves fetal survival rates of ~90% overall and ~95% in non-hydropic fetuses, with procedure-related loss rates around 1–2% per transfusion in experienced centers Liley 1963 Zwiers et al. 2017.

Protocol

Standard of care in high-income obstetric systems, distilled from ACOG 2017 and parallel guidelines (RCOG, NICE, SOGC, FIGO):

• First prenatal visit: ABO and RhD typing on the pregnant person, plus an antibody screen (indirect Coombs / indirect antiglobulin test). If RhD-negative and screen-negative, the patient is a candidate for prophylaxis.
• Paternal RhD typing when feasible: if the biological father is RhD-negative, no prophylaxis is needed (fetus is necessarily RhD-negative). If RhD-positive heterozygous (genotype Dd), the fetus has a 50/50 chance of being RhD-positive.
• Cell-free fetal DNA (cffDNA) RhD genotyping on a maternal blood sample, available routinely in many European programs (Denmark, the Netherlands, Finland, parts of the UK and France) since the early 2010s. About 35–40% of RhD-negative pregnancies carry an RhD-negative fetus; targeted prophylaxis avoids unnecessary RhIG exposure for those pregnancies Finning et al. 2008 Tiblad et al. 2013.
• Antenatal RhIG: a single 300 μg (1500 IU) intramuscular dose at 28 weeks (alternative European regimen: 100–125 μg at 28 and 34 weeks). Repeat antibody screen first to confirm the patient is not already immunized.
• Postpartum RhIG: within 72 hours of delivery if the newborn is RhD-positive (or RhD-unknown). All RhD-negative women with RhD-positive infants are screened for excessive fetomaternal hemorrhage (rosette test, then Kleihauer-Betke or flow cytometry if positive); dose is increased by ~10 μg per mL of fetal whole blood beyond the standard 30 mL coverage the 300 μg dose covers.
• Sensitizing-event RhIG: after miscarriage, ectopic, induced abortion, chorionic villus sampling, amniocentesis, cordocentesis, external cephalic version, antepartum bleeding, abdominal trauma, or any procedure with bleeding risk. Mini-dose (50–150 μg) suffices in the first trimester; 300 μg from the second trimester onward.
• If already alloimmunized: serial antibody titers, paternal/fetal RhD genotyping, MCA-PSV Doppler every 1–2 weeks from ~18 weeks onward, with intrauterine transfusion when MCA-PSV exceeds 1.5 MoM or hydrops appears. Referral to a maternal–fetal medicine center is the standard.

Contraindications

Anti-D immune globulin is exceptionally well-tolerated. Absolute contraindications are limited to documented anaphylactic reaction to previous human IgG products and to pre-existing alloimmunization to RhD (which makes prophylaxis pointless). Selective IgA deficiency with anti-IgA antibodies is a relative caution because trace IgA in the preparation can trigger reactions. Common side effects are limited to mild injection-site reaction, low-grade fever, occasional headache, and rare allergic rash. The product is plasma-derived, so theoretical concern about blood-borne pathogen transmission exists; modern viral inactivation has produced no documented HIV, HBV, HCV, or HEV transmissions in decades, and serological tracking of recipients shows pathogen marker rates indistinguishable from controls. Hemolysis from passive anti-D destroying the patient's own red cells is a theoretical risk reserved for the rare RhD-positive recipient (an irrelevant scenario in standard prophylaxis).

Misconceptions

Several persistent confusions deserve naming:

• "Rh incompatibility means I can't have children with an Rh-positive partner." False — Rh incompatibility is a fully managed condition in any modern obstetric system. The risk is to subsequent RhD-positive pregnancies if the first one sensitizes; prophylaxis prevents that sensitization, leaving family-building unconstrained.
• "It only matters from the second pregnancy onward, so I can skip RhIG in the first." Half-true and dangerous. The first pregnancy is when sensitization happens — the disease is in the second. Skip RhIG in the first pregnancy and the second pregnancy may be the catastrophe.
• "Anti-D is the same as the antibody I'd make myself." Structurally yes, functionally opposite. Endogenous anti-D from active sensitization is durable, memory-encoded, and harmful. Exogenous anti-D administered passively clears within ~12 weeks, never produces memory, and prevents the active response from forming in the first place.
• "ABO incompatibility is the same problem." Different mechanism, much milder clinical course. Naturally occurring anti-A and anti-B are predominantly IgM and cross the placenta poorly; ABO HDFN is usually limited to mild neonatal jaundice without antenatal anemia, and requires no antenatal prophylaxis.
• "If I'm Rh-negative and my partner is Rh-negative, I still need the shots." No — if paternity is certain, the fetus is necessarily RhD-negative and prophylaxis adds nothing.

Stakes

The pre-prophylaxis trajectory is the reference point. A first sensitizing event might produce no neonatal disease at all; the second RhD-positive pregnancy can produce moderate hemolysis; each subsequent affected pregnancy tends to be worse than the last, because maternal anti-D titer climbs with each exposure. Without intervention, severe HDFN classically presents as hydrops fetalis with intrauterine death from the late second trimester onward, or, if the fetus survives to birth, profound neonatal anemia and bilirubin encephalopathy producing permanent cerebral palsy, deafness, choreoathetosis, and gaze palsy. In settings without prophylaxis, around 14% of affected fetuses are stillborn, and approximately half of live-born affected infants die or sustain brain injury Pegoraro et al. 2020. Once a woman is sensitized, the immunity is lifelong: every subsequent RhD-positive pregnancy is high-risk, and the option to have more children is constrained by what intrauterine-transfusion-capable maternal-fetal-medicine centers can offer.

Payoff

For the universally-screened, universally-prophylaxed pregnancy: nothing happens, which is the point. The pregnant person receives two injections (28 weeks and postpartum if applicable) and the baby is born with normal hemoglobin and bilirubin. The pregnancy after that — and the one after that, however many a family chooses — proceeds without an immunological cliff. For the small remainder who are already immunized at entry, MCA-PSV monitoring detects fetal anemia early, intrauterine transfusion restores fetal hematocrit when needed, and ~90% of affected fetuses now survive in expert centers, most without long-term sequelae Zwiers et al. 2017. The cumulative population-level payoff over five decades of universal prophylaxis: Rh disease shifted from being a major cause of perinatal mortality to a footnote in obstetric morbidity in any country with a functional antenatal program.

Practicalities

In high-income systems, RhIG is supplied through obstetric clinics and labor-and-delivery units; the patient does not source it, only consents to it. Cost in the US ranges from roughly $100–250 per dose (insurance-covered in any standard prenatal plan); cost in NHS-style systems is absorbed into antenatal care; cost in cash-pay obstetric markets in low-income settings is the binding constraint and the reason coverage rates lag. The injection is intramuscular (usually deltoid); discomfort is on the order of a routine vaccine. Cell-free fetal DNA RhD genotyping costs roughly $200–600 in US markets and is reimbursed by some insurers; in Danish and Dutch national programs it is integrated into the antenatal panel at no patient cost.

Audience

Direct relevance: anyone who is RhD-negative and is, may become, or could become pregnant. Indirect relevance: any partner of an RhD-negative person planning a pregnancy (paternal RhD status determines whether the fetus is at risk); any family member supporting such a pregnancy. Population-prevalence patterns: RhD-negative status is most common in people of European ancestry (~15%), less common in African (~3–8%) and South Asian populations, and rare (under 1%) in East Asian populations — which influences both the absolute size of the at-risk population by region and the realistic priorities of national antenatal programs.

Alternatives

For prophylaxis: no clinically equivalent alternative to anti-D IgG exists. Recombinant monoclonal anti-D has been developed and tested but has not displaced polyclonal plasma-derived product, which remains standard de Haas et al. 2015. For monitoring an alloimmunized pregnancy, MCA-PSV Doppler has largely replaced serial amniocentesis (delta-OD₄₅₀ bilirubin measurement) for the same indication — less invasive, more sensitive Mari et al. 2000. For rescue therapy when fetal anemia is present, intrauterine transfusion is the only effective option; IVIG and maternal plasmapheresis have been trialed adjunctively in early-onset severe disease but do not replace transfusion.

Failure modes

Residual failures of universal prophylaxis trace to a small number of recurring causes ACOG 2017 Tiblad et al. 2013:

• Missed antenatal dose — patient lost to follow-up, late prenatal care, or forgotten 28-week appointment.
• Missed postpartum dose — discharge before the 72-hour window expires without the shot, especially in disrupted care settings.
• Missed sensitizing event — bleeding, trauma, or a procedure not recognized as warranting RhIG, especially in emergency departments unfamiliar with the protocol.
• Underdosing — a large fetomaternal hemorrhage at delivery not detected by rosette test, so the standard 300 μg dose was insufficient to neutralize the fetal red cell load.
• Silent third-trimester sensitization — small fetomaternal hemorrhages before 28 weeks that escape detection and the antenatal dose; this is the residual baseline ~0.1–0.2% the program cannot fully close.

History

Karl Landsteiner and Alexander Wiener identified the Rh antigen in 1939; Philip Levine described the immunological basis of erythroblastosis fetalis the following year. For two decades the disease was a leading cause of perinatal mortality in Rh-negative women on their second-or-later pregnancy. William Liley performed the first intrauterine transfusion in Auckland in 1963 — intraperitoneal injection of compatible donor blood, guided by paper clips taped to the mother's abdomen as X-ray landmarks; survival rates were poor but the proof of principle was decisive Liley 1963. Vincent Freda, John Gorman, and William Pollack at Columbia and Ortho Diagnostics tested passive anti-D IgG as a prophylactic in the 1960s; the pivotal Sing Sing Prison trial in Rh-negative male volunteers (intentionally challenged with RhD-positive cells and then given anti-D) established efficacy. RhoGAM received FDA approval in 1968 for postpartum administration; ACOG endorsed routine antenatal prophylaxis at 28 weeks in 1981 Pollack et al. 1968 Bowman 1988.

Out-of-scope

Closely-related topics worth their own future entries: other red-cell alloimmunization syndromes (anti-Kell, anti-c, anti-E — same monitoring playbook, different antigens, no analogous prophylaxis available); ABO HDFN (different mechanism, milder course, no antenatal management); neonatal phototherapy and exchange transfusion for severe neonatal hyperbilirubinemia (downstream rescue, not prevention); routine prenatal care more broadly (antibody screen is one panel among many); fetal–maternal hemorrhage in trauma (overlaps with the sensitizing-event protocol but is a broader obstetric topic).

The credibility range

Optimist case

Anti-D prophylaxis is among the highest-impact, lowest-cost preventive interventions in all of medicine. The pre-1968 baseline alloimmunization rate (~13–16% of at-risk pregnancies) crashed to ~0.1–0.2% with the full antenatal + postpartum protocol, an order-of-magnitude reduction that has held across millions of pregnancies and five decades of post-market surveillance ACOG 2017 Bowman 1988. The evidence is multi-trial, replicated across continents, mechanism-coherent, guideline-aligned across every major obstetric body (ACOG, RCOG, NICE, SOGC, FIGO, WHO), and saves an estimated 160,000+ perinatal lives per year of remaining unmet need where coverage gaps still exist Bhutani et al. 2013. The intervention itself is a single intramuscular shot with a side-effect profile lighter than that of a routine vaccine. The monitoring stack for the residual alloimmunized minority — MCA-PSV Doppler, intrauterine transfusion in MFM centers — pushes survival in affected pregnancies above 90%. There is essentially no skeptic case against the core protocol within mainstream obstetrics.

Skeptic case

The closest things to legitimate skepticism are not about whether RhIG works — that question is settled — but about three adjacent issues. First, overuse and resource waste: in standard practice without cell-free fetal DNA genotyping, ~35–40% of RhD-negative women receive prophylaxis their pregnancy didn't need (the fetus is RhD-negative), consuming a finite plasma-derived product at scale Finning et al. 2008. Second, RhIG in early miscarriage: ACOG's 2024 Clinical Practice Update reflects an emerging consensus that pregnancy loss under 12 weeks is unlikely to cause sensitization and may not warrant RhIG, narrowing one historical indication. Third, plasma-derived-product theoretical risks: the product is human plasma derivative and carries the floor-level theoretical risk of any blood product; this is a real consideration in vaccine-hesitant patient populations, though the actual track record is reassuring. None of these unsettle the core recommendation; they refine its edges.

Author's call

This is one of the few entries in the catalogue where the evidence-rating ceiling is fully earned. The intervention is the textbook example of a primary prevention strategy that altered the natural history of a disease at population scale. The article should be unambiguous about that — no hedging, no "studies suggest" — and should treat the reader's job as ensuring the protocol is actually delivered (clinic asks for antibody screen, schedules the 28-week shot, delivers the postpartum shot, covers sensitizing events). The complication arc — what to do if the patient is already immunized — gets a paragraph; for the unimmunized RhD-negative reader, the article is short and decisive.

Stakeholder + incentive map

• Patient advocacy and global health bodies (WHO, FIGO, ICM): push for universal coverage in low-income settings where Rh disease still kills; aligned with the optimist case.
• Obstetric professional bodies (ACOG, RCOG, NICE, SOGC): set and refine the protocol; aligned and conservative — slow to update when new evidence (cffDNA targeting, narrower early-loss indication) accumulates but eventually consolidates around it.
• Plasma-derived-product manufacturers (Kedrion, Grifols, CSL Behring): commercial incentive to maintain the broad-prophylaxis indication that drives demand; modest interest in targeted-prophylaxis programs that would shrink that demand.
• Diagnostic companies offering cffDNA RhD typing: commercial incentive to expand targeted prophylaxis; aligned with European national programs that have adopted it.
• Vaccine-hesitant communities: occasional resistance to "another injection in pregnancy," sometimes generalized from concerns about other plasma-derived or vaccine products; not a mainstream position but a clinically real source of declined RhIG.
• Low-income-country health systems: structural under-coverage driven by cost, supply, and antenatal-care reach, not by skepticism. The unfinished half of the prophylaxis revolution.

Population variability

Population-level RhD-negativity rates determine who is at risk and shape national program priorities. RhD-negative prevalence: ~15% in European-ancestry populations (highest in Basque and Cantabrian regions, ~30%), 3–8% in African-ancestry populations, ~5% in South Asian populations, and under 1% in East Asian populations. Within an at-risk RhD-negative woman: the magnitude of fetomaternal hemorrhage at any sensitizing event is the binding variable — most exposures are small (<0.5 mL fetal blood) and well-covered by standard prophylaxis, while rare large hemorrhages (placental abruption, abdominal trauma, manual placental extraction) can exceed the protective dose and require KB-test-guided supplementation. Already-sensitized pregnancies vary widely in severity depending on antibody titer trajectory, fetal RhD status (a heterozygous father gives 50/50 odds the current fetus is RhD-negative and unaffected), and gestational age at antibody emergence. Obese patients have slightly higher rates of prophylaxis failure, possibly from IM injection depot variability.

Knowledge gaps

Open questions in the field: (1) the precise lower gestational-age threshold below which a sensitizing event genuinely does not require RhIG — the 2024 ACOG update narrows the indication for <12-week losses but the dataset is observational; (2) whether universal targeted prophylaxis via cffDNA RhD typing should replace empirical antepartum RhIG in all high-income systems, a cost-effectiveness question that the European national programs have largely answered "yes" and the US has not yet adopted at scale; (3) optimal management of the rarer non-D alloimmunizations (anti-Kell in particular, which causes severe HDFN by suppressing fetal erythropoiesis rather than purely by hemolysis, and for which no prophylaxis exists); (4) the long-term immunological safety profile of repeated antenatal RhIG exposure across multiple pregnancies, which is empirically clean over five decades but has no mechanistic guarantee of continued safety as products and donor pools evolve; (5) closing the global coverage gap in low-income settings, which is operational and economic rather than scientific.

Scope match to brief. The brief named antibody screening, anti-D immune globulin, fetal/newborn anemia and jaundice, current and future pregnancy risk, and monitoring + injections. All covered: mechanism handles the immune-memory story and HDFN naming, evidence covers the prophylaxis history and effect sizes, protocol covers the screen + injection schedule + sensitizing-event triggers, audience covers the already-sensitized branch with MCA Doppler and intrauterine transfusion, stakes covers anemia/jaundice/kernicterus and the current/future-pregnancy escalation.

Action type call. Chose know over do or respond. The injections are clinician-delivered; the reader's actionable behavior is awareness + advocacy (confirm the screen, confirm the 28-week dose, flag sensitizing events). Not do — the reader doesn't self-administer. Not respond — the protocol doesn't trigger on a symptom the reader perceives; it triggers on the diagnosis itself.

Audience scoping. Limited to female and primarily 18-39, matching the reproductive window. Could be argued to include 40-59 (later pregnancies do happen and the protocol is identical), but the volume is small enough that the narrower scoping is the honest call. Partners and family who'd want to know are not really an audience-scoping concern; that's served by general discoverability.

Mood scoring at 2 was the hardest call. The scoring framework's benefit dimensions don't have a slot for "fetal/newborn outcomes prevented" — all the heavy lifting an Rh prophylaxis entry does lands on the fetus, not the rated reader. The mood score captures the genuine relief an Rh-negative person gets from knowing the catastrophe trajectory is solved, but understates the entry's importance from a public-health perspective. The article carries the urgency through stakes and the dek rather than relying on the score to convey it.

Applicability at 2. RhD-negative women of reproductive age sum to roughly 4–8% of the global adult population depending on ancestry mix. The "decision audience" lift (partners, family, anyone who could one day be pregnant) is real but bounded — this isn't a universal-prenatal-care entry, it's a specific-population one. Resisted the urge to lift to 3.

Dream narrative written despite score < 40. Overall score computes to ~12 (high evidence + low burdens, but most benefit dimensions zero, applicability 2). Narrative warranted under the relief lever: the pre-1968 trajectory (worsening Rh-positive pregnancies, families losing children) is real and the modern protocol fully solves it. Dek and tagline lean on that relief; tagline does the work plainly without the narrative-driven crank that 40+ would license.

Related entries to wire when they exist:

• Routine prenatal care / first-visit blood panel — the parent entry this would link into.
• Other red-cell alloimmunization (anti-Kell, anti-c, anti-E) — different antigens, similar monitoring, no prophylaxis. Separate-entry candidate.
• ABO hemolytic disease of the newborn — distinct mechanism, milder course. Separate-entry candidate (and worth one for misconception management — readers commonly conflate them).
• Neonatal jaundice / phototherapy / exchange transfusion — downstream treatment surface.
• Sensitizing events in pregnancy (trauma, bleeding, amniocentesis) — could warrant its own protocol entry given the cross-cutting "tell the obstetric team inside 72 hours" pattern.

Deliberate exclusions:

• Detailed maternal-fetal medicine management of severe alloimmunization (intrauterine transfusion technique, IVIG adjuncts, plasmapheresis) — not the reader's decision space; covered at the level of "this exists and works" in the audience section.
• Cell-free fetal DNA RhD typing got a paragraph rather than a section — it's mostly a European program detail and the US reader's actionable move is to ask whether it's available, which the protocol section handles in one line.
• The 2024 ACOG clinical practice update on RhIG for pregnancy loss under 12 weeks — narrowing indication, but mid-flight in the field. Article uses the conservative all-trimester sensitizing-event framing; a revision can narrow that once SMFM and ACOG converge.
• No mention of recombinant monoclonal anti-D candidates — they exist but haven't displaced polyclonal; clutter without action value.

Rating difficulties: evidence at 5 is fully earned — multiple randomized trials, replicated across continents, 50+ years of post-market data, aligned across every major guideline body. One of the few entries where the ceiling is the honest call rather than a generous one.