Rh-Negative Pregnancy & Alloimmunization
Rh (Rhesus) alloimmunization occurs when an Rh-negative mother is exposed to Rh-positive fetal red blood cells, triggering the development of anti-D antibodies. These antibodies can cross the placenta in subsequent pregnancies, causing Hemolytic Disease of the Fetus and Newborn (HDFN).
Key Management Concepts
- Screening: Blood group and antibody screen are performed at the first antenatal visit. If the mother is Rh-negative and sensitized (antibody positive), the pregnancy is monitored as high-risk.
- Prophylaxis: Anti-D immunoglobulin is administered to non-sensitized Rh-negative women to prevent the development of anti-D antibodies.
Indications for Anti-D Prophylaxis
| Timing | Indication |
|---|---|
| Routine | Prophylactic dose at 28 weeks of gestation (and sometimes at 34 weeks). |
| Sensitizing Event | Post-miscarriage, ectopic pregnancy, termination, amniocentesis, trauma, or APH. |
| Post-Delivery | Within 72 hours of delivery, if the infant is confirmed Rh-positive. |
High-Yield Exam Pearl:
- Kleihauer-Betke Test: Used after a significant sensitizing event (like major abdominal trauma) to quantify the volume of fetomaternal hemorrhage and determine if additional doses of Anti-D are required.
- Hydrops Fetalis: The most severe manifestation of untreated HDFN, characterized by fetal anemia, edema, ascites, and pericardial/pleural effusions.