Rh Factor: Complete Guide
Understanding Rh positive and negative blood types, inheritance patterns, and medical importance.
Rh Positive (+)
Has the Rh factor (D antigen) on red blood cells. About 85% of people are Rh positive.
- •Can receive Rh+ or Rh- blood (if ABO compatible)
- •Most common across all ethnicities
- •Inherited as a dominant trait
Rh Negative (-)
Lacks the Rh factor (D antigen). About 15% of people are Rh negative.
- •Can only receive Rh- blood (if ABO compatible)
- •More common in Caucasian populations
- •Inherited as a recessive trait
What is the Rh Factor?
The Rh factor is a protein (specifically the D antigen) that can be present on the surface of red blood cells. If you have this protein, you're Rh positive. If you don't have it, you're Rh negative.
The name "Rh" comes from rhesus monkeys, where the protein was first discovered in scientific research. Along with ABO blood types, the Rh factor is one of the most important blood type classifications used in medicine.
How Rh Factor is Inherited
The Rh factor follows simple genetic inheritance patterns:
- ✓Rh Positive is Dominant: You only need one Rh+ gene from either parent to be Rh positive
- ✗Rh Negative is Recessive: You need two Rh- genes (one from each parent) to be Rh negative
Inheritance Examples:
Both parents Rh positive:
Child can be Rh+ or Rh- (if both parents carry hidden Rh- gene)
One parent Rh+, one parent Rh-:
Child is usually Rh+, but can be Rh- depending on parents' genes
Both parents Rh negative:
Child will always be Rh negative (100%)
Rh Factor in Pregnancy
Rh incompatibility can cause complications during pregnancy when an Rh negative mother carries an Rh positive baby.
⚠️ What Happens During Rh Incompatibility:
- Rh- mother becomes pregnant with Rh+ baby (inherited from Rh+ father)
- During pregnancy or delivery, baby's blood can mix with mother's blood
- Mother's immune system sees baby's Rh+ cells as foreign and creates antibodies
- In future pregnancies, these antibodies can attack Rh+ babies' red blood cells
- This can cause hemolytic disease of the newborn (HDN), a serious condition
RhoGAM: The Solution
Modern medicine has solved this problem with RhoGAM (Rh immune globulin) injections:
- 💉Given to Rh- mothers at 28 weeks of pregnancy and within 72 hours after delivery
- 💉Prevents mother's immune system from creating antibodies against Rh+ blood
- 💉Also given after miscarriage, abortion, or any event where blood mixing might occur
- 💉Must be given with each pregnancy to remain effective
RhoGAM has made Rh incompatibility complications rare in modern healthcare settings where prenatal care is available.
Rh Factor and Blood Transfusions
The Rh factor is critical for safe blood transfusions:
✓ Safe Transfusions
- Rh+ patients: Can receive Rh+ or Rh- blood
- Rh- patients: Should only receive Rh- blood
✗ Dangerous Transfusion
- Rh- patient receives Rh+ blood: Can cause immune reaction
- Body produces antibodies against Rh factor
- Future transfusions become increasingly risky
Frequently Asked Questions
Can two Rh positive parents have an Rh negative child?
Yes! If both parents are Rh positive but carry a hidden Rh negative gene (genotype +/-), they have a 25% chance of having an Rh negative child who inherits both recessive genes.
Why is O negative called the universal donor?
O negative blood lacks A, B, and Rh antigens, so it can be given to anyone in emergencies without causing immune reactions. The "negative" part is crucial - O positive cannot be given to Rh negative patients.
Do I need RhoGAM if I'm Rh positive?
No. RhoGAM is only needed for Rh negative mothers who might be carrying or have carried an Rh positive baby. If you're Rh positive, there's no risk of Rh incompatibility.
Is being Rh negative rare?
It depends on ethnicity. About 15% of Caucasians are Rh negative, but only 4-7% of African Americans and less than 1% of Asians. Globally, about 85% of people are Rh positive.
Does Rh factor affect my health otherwise?
No. The Rh factor itself doesn't affect your daily health or medical conditions. It only matters for blood transfusions and pregnancy situations involving Rh incompatibility.
Learn More
Medical Disclaimer: This information is provided for educational purposes only. Always consult with healthcare professionals for medical advice regarding pregnancy, blood transfusions, and Rh incompatibility management. If you're pregnant and Rh negative, discuss RhoGAM with your obstetrician.