Yes, Rh negative is a recessive trait. You are Rh negative only when both copies of the gene you inherited lack the Rh factor, so one working copy from either parent is enough to make you Rh positive.1The Tech Interactive. Beyond A, B, O: Why is our blood type positive or negative? Being Rh negative usually isn’t a sign that anything is wrong in your body. It mostly matters for blood transfusions and pregnancy. And because the negative version can hide for generations behind a positive one, two Rh-positive parents are sometimes surprised by an Rh-negative baby.
What The Plus Or Minus In Your Blood Type Means
The Rh factor (RhD) is a protein called D that sits on the surface of red blood cells. The plus or minus after your A, B, AB or O type says whether you have it.2PubMed Central. Karl Landsteiner: A Versatile Blood Scientist Several Rh proteins exist, but D is the one most likely to provoke the immune system, so in everyday use “Rh factor” means D.3PubMed Central. Karl Landsteiner: A Versatile Blood Scientist The name comes from rhesus monkeys, whose blood was used when the factor was first found in 1940.4PubMed Central. Karl Landsteiner: A Versatile Blood Scientist
The D protein is made by a gene called RHD on chromosome 1, next to a very similar gene that makes other Rh proteins.5PubMed. Gene organization and rearrangements at the human Rhesus blood group locus revealed by fiber-FISH analysis In most Rh-negative people, the RHD gene isn’t damaged. It is entirely missing from the chromosome.6PubMed Central. Molecular genetics and clinical applications for RH
On a blood type label, the Rh part is added to the ABO part. O negative means type O blood with no D protein, and A positive means type A with D present. The two systems are inherited separately, so knowing one tells you nothing about the other. Your lab report or donor card may write the result as “RhD negative,” “Rh-” or “D negative.” All mean the same thing.
Typing is a yes-or-no test. A drop of blood is mixed with an anti-D reagent, and the lab watches whether the red cells clump together. Clumping means D is present and the result is positive. No clumping means negative.
Why Rh Negative Is Recessive
Everyone inherits two copies of the RHD gene, one from each parent.7The Tech Interactive. Beyond A, B, O: Why is our blood type positive or negative? A dominant trait like Rh positive shows up with just one working copy, while a recessive trait needs two.8The Tech Interactive. Beyond A, B, O: Why is our blood type positive or negative? So an Rh-negative person has two copies that are deleted or don’t work.9The Tech Interactive. Beyond A, B, O: Why is our blood type positive or negative?
An Rh-positive person, on the other hand, can have two working copies or one working copy and one negative copy. Someone with one hidden negative copy is a carrier: they can pass that copy to their children without ever showing it. In people of European descent, roughly 40% of these gene copies are the deleted negative version,10PubMed. RHD gene deletion occurred in the Rhesus box so many Rh-positive people of European descent are carriers without knowing it.
Geneticists write a working copy as D and a missing one as d. People who are DD or Dd both test Rh positive, and only dd people test Rh negative. A standard blood type test can’t tell DD from Dd, since both show the protein.
The missing copy can pass through several generations of positive people unnoticed. It shows up only when a child receives a negative copy from both parents.
That also explains why a parent’s type may not match what they pass on. A parent hands each child only one of their two copies, chosen by chance, so a Dd parent passes on either D or d. That’s how a positive parent can have a negative child, and why siblings can differ from one another.
Your Baby’s Rh Type Based On Both Parents
- Two Rh-negative parents (dd and dd): nearly all children will be Rh negative.
- Rh-negative parent and DD positive parent: every child will be Rh positive.
- Rh-negative parent and Dd positive parent: each child has a 1 in 2 chance of being Rh negative.
- Two Dd positive parents: each child has a 1 in 4 chance of being Rh negative.
- DD positive parent and any other positive parent: every child will be Rh positive.
Each parent contributes one copy by chance, like two separate coin flips, one from each side. A Dd parent has an equal chance of passing D or d, which is where the 1 in 2 and 1 in 4 odds come from. A negative parent always passes d, so the child’s type depends on what the other parent passes.
The odds reset with every pregnancy. Two carrier parents could have several positive children and then a negative one. A 1 in 4 chance doesn’t guarantee one negative child in every four; a family of four could have none or several. The percentages also apply only if both parents’ hidden genes are actually known.
Most positive parents only know they are “positive,” not whether they’re DD or Dd. An Rh-negative child or grandparent in the family hints that a positive parent is a carrier. If it matters for your plans, a positive partner’s exact genes can be tested, so ask your doctor before assuming.
Why Rh Type Matters In Pregnancy
If an Rh-negative mother’s body is exposed to the red cells of an Rh-positive baby, which carry the father’s D protein, she can make antibodies against them.11PubMed. Hemolytic Disease of the Fetus and Newborn: Modern Practice and Future Investigations A transfusion of Rh-positive blood can cause the same reaction.12PubMed. Hemolytic Disease of the Fetus and Newborn: Modern Practice and Future Investigations Once her body has made these antibodies, a later Rh-positive baby can have its red cells attacked, a condition called hemolytic disease of the fetus and newborn.13PubMed. Hemolytic Disease of the Fetus and Newborn: Modern Practice and Future Investigations
The first baby is usually safe. Sensitization takes time, and the main exposure to the baby’s blood usually comes late, at delivery. By then the pregnancy is over, so her immune system has little chance to harm that baby. The antibodies she makes afterward stay in her body, ready the next time she carries an Rh-positive baby. When mother and baby also have mismatched ABO types, her body is somewhat less likely to become sensitized.14PubMed Central. EFFECT OF ABO INCOMPATIBILITY ON PREGNANCY-INDUCED RH ISOIMMUNIZATION.
Mixing of blood is most likely at birth, but it can also happen after miscarriage, abortion, ectopic pregnancy, bleeding in pregnancy, a blow to the belly, and some prenatal procedures. Tell your care team about any of these, since they are moments for preventive treatment.
In the affected baby, red cells break down faster than they’re made, causing anemia. Newborns can develop jaundice, a yellowing from the breakdown products. Severe cases need close monitoring and sometimes transfusions before or after birth.
If the baby is Rh negative like her, there is no mismatch and no risk of this kind. If the father is Rh negative too, the baby will almost always be negative, which is why his type matters here.
How The Anti-D Shot Protects Future Babies
Rh-negative pregnant women are offered an anti-D shot (Rh immune globulin, often sold as RhoGAM), made of ready-made antibodies against D. It clears the baby’s Rh-positive cells from her blood before her own immune system can learn to react to them.15PubMed. Mechanisms of anti-D action in the prevention of hemolytic disease of the fetus and newborn That makes it preventive: it doesn’t help once she has already made her own antibodies. The anti-D shot is commonly given around 28 weeks, after birth if the baby is positive, and after events like bleeding. If the baby turns out to be Rh negative, the after-birth dose is generally not needed.
A blood test on the mother from about 9 weeks of pregnancy can read the baby’s RHD genes from DNA in her blood.16PubMed Central. Clinical Validation of a Prenatal Cell-Free DNA Screening Test for Fetal RHD in a Large U.S. Cohort That lets shots be limited to women actually carrying an Rh-positive baby.17PubMed Central. Clinical Performance of Cell-Free DNA for Fetal RhD Detection in RhD-Negative Pregnant Individuals in the United States These tests are built to detect the common nonworking RHD versions, which helps avoid wrong results.18PubMed. The use of free DNA for fetal RHD genotyping in the Rh negative pregnant patient-the time has come
It is a single injection, usually into a muscle in the arm or buttock. Soreness at the site is the most common side effect. You’ll have antibody screening blood tests along the way to check whether you have made antibodies of your own.
At your prenatal visit, ask whether your clinic offers the fetal RhD blood test and whether insurance covers it. Ask when your shot is scheduled and what to do if you bleed between visits. If the father is known to be Rh negative, ask whether that changes your plan.
How Common Rh Negative Is Around The World
About 15% of people of European descent are Rh negative, matching the 85% positive found in 1940. The Basque population has the world’s highest rate, roughly 30 to 35% Rh negative.19bioRxiv. A Quantitative Model for RhD-Negative Allele Frequency Peaks in Ibero-Berber Populations via Synergistic Selection Some Berber groups in North Africa run about 15 to 20%.20bioRxiv. A Quantitative Model for RhD-Negative Allele Frequency Peaks in Ibero-Berber Populations via Synergistic Selection At the other end, in one Ethiopian region, 91% of people tested were Rh positive.21International Journal of Scientific Reports. Distribution of ABO and Rh (D) allele frequency among the populations of Yilmana Denssa and Mecha, Ethiopia In many East Asian populations Rh negative is under 1%. In people of African descent, a nonworking RHD gene rather than a missing one is relatively common.22PubMed Central. Molecular genetics and clinical applications for RH Rates are group averages, so any individual of any ancestry can be either type.
For blood donation, O-negative blood is given in emergencies when a patient’s type is unknown. Shortages of it happen often, so Rh-negative donors are especially needed.
Weak D And Other Unusual Rh Results
Some people make a D protein that is reduced or altered, so standard tests give weak or confusing results.23PubMed Central. Serological weak D phenotypes: A review and guidance for interpreting the RhD blood type using the RHD genotype Labs now use gene tests to sort these into types such as weak D and partial D.24PubMed Central. Serological weak D phenotypes: A review and guidance for interpreting the RhD blood type using the RHD genotype In weak D, the D protein is present but in smaller amounts than usual, so a standard test may barely detect it. In partial D, some parts of the protein are missing, so the immune system may see it as partly foreign. The two can call for different handling in transfusion and pregnancy, and depending on the type, a person may be treated as positive for some purposes and negative for others.
Results can change between labs because different labs use different reagents and methods, and these vary in how well they pick up weak versions of D. One lab may call you positive while another calls you negative. A gene test settles the matter by reading the RHD gene itself instead of relying on how strongly the cells react.
If your report says weak D, ask whether a gene test was done to confirm the exact variant. Ask whether you should get the anti-D shot in pregnancy, and how your type should be listed for transfusions so records stay consistent.
Very rarely, a person lacks all Rh proteins, called Rh-null, which causes a mild ongoing anemia.25Blood. Hematological Observations on the Anemia Associated with Blood Type Rhnull Rh-null red cells have abnormal shape and leak salts, so they break down early.26PubMed. RH blood group system and molecular basis of Rh-deficiency
Does Being Rh Negative Affect Your Health
In one online survey, Rh-negative people reported certain health problems more often and others less often than Rh-positive people.27PubMed Central. Worse Health Status and Higher Incidence of Health Disorders in Rhesus Negative Subjects In pregnant women at term, Rh-negative status didn’t clearly raise COVID-19 infection risk.28PubMed Central. SARS-CoV-2 Infection Susceptibility of Pregnant Patients at Term Regarding ABO and Rh Blood Groups: A Cohort Study So outside pregnancy and transfusion, Rh negative alone isn’t a reason for extra screening or worry.
Your type is on prenatal records, donor cards, or past hospital lab results. Donating blood often gets your type reported back to you for free. Keep the result with your medical records in case of an emergency or pregnancy.