What is Rh Incompatibility?
Rhesus (Rh) incompatibility is a condition that happens when a mother and her unborn child have two different blood types- Rh-positive and Rh-negative. This can cause some health issues. For example, when a mother who is Rh-negative gets exposed to an Rh-positive baby’s blood, her body may start to develop Rh sensitization. This means her body creates anti-D antibodies which will try to attack the Rh-positive blood cells.
We can classify people as Rh-positive if they have an Rh D antigen in their red blood cells, or as Rh-negative if they don’t. This can lead to problems if a mother who is Rh-negative develops these antibodies and they bind to and potentially destroy Rh-positive blood cells.
If a mother who is Rh-negative is carrying a baby who is Rh-positive, it may result in a condition known as Hemolytic disease of the neonate (HDN). This is a range of problems that can occur in a newborn baby. The issues can range from mild anemia, which is a condition where there aren’t enough healthy red blood cells to deliver adequate oxygen to the body’s tissues, to severe hydrops fetalis, a serious condition in which an excessive amount of fluid builds up in two or more body areas of a fetus or newborn.
What Causes Rh Incompatibility?
As we discussed, a mother with Rh-negative blood can develop a reaction or “sensitization” to an Rh-positive baby she’s carrying. This reaction can also happen if she comes into contact with Rh-positive blood in another way. However, if her first contact with the Rh D antigen (a marker found in Rh-positive blood) happens during her first pregnancy, it usually doesn’t harm that pregnancy. This is because the baby is usually born before the mother’s body can make anti-D antibodies (proteins that fight off Rh D). But once a mother has had this reaction, future babies are at risk if they are Rh-positive. This can lead to a condition called Hemolytic Disease of the Newborn (HDN), which is caused by blood type incompatibility between the mother and baby.
Risk Factors and Frequency for Rh Incompatibility
Rh incompatibility is related to the prevalence of Rh-negative blood types, which differs among various groups of people. It’s more common in people of North American or European descent, compared to those from African or Asian backgrounds. The occurrence of Rh disease is notable worldwide, leading to high rates of mortality or brain damage in untreated cases. Nonetheless, in developed countries, the prevalence is lower due to better maternal and newborn healthcare.
- Rh-negative blood types are more commonly found in Caucasians (15% to 17%) than in Africans (4% to 8%) or Asians (0.1% to 0.3%).
- Rh disease occurs in an estimated 276 out of every 100,000 live births across the globe.
- About 50% of untreated Rh disease cases result in death or brain damage.
- On the other hand, developed countries have lower rates — 2.5 out of every 100,000 live births — due to better perinatal-neonatal care.
Signs and Symptoms of Rh Incompatibility
Rh-negative mothers who are sensitized to the D antigen might have been exposed to it through a number of ways. This exposure could be from Rh-positive blood from the baby or from non-baby sources. A detailed history can help identify potential occasions when the exposure may have occurred. For the mother, Rh incompatibility usually does not cause any noticeable symptoms. However, the effects on an Rh-positive baby can be serious. The baby can experience symptoms like lethargy, pallor, yellowing of skin and eyes, fast heartbeat, rapid breathing, and low blood pressure. In severe cases, the baby might develop a life-threatening condition called Hydrops fetalis. This condition involves severe anemia and fluid buildup in at least two parts of the body, and it has an estimated mortality rate of over 50%.
Exposure to the baby’s Rh-positive blood can come from:
- Delivery (either vaginal or Cesarean section)
- Threatened miscarriage or miscarriage
- Bleeding during pregnancy from conditions like placenta previa, abruptio placentae, vasa previa, or uterine rupture
- Trauma
- External cephalic version
- Invasive procedures (such as chorionic villus sampling or amniocentesis)
- Ectopic pregnancy
- Molar pregnancy
Non-baby exposure to Rh-positive blood can come from:
- Transfusion
- Bone marrow transplantation
- Needle-stick injury
Testing for Rh Incompatibility
Rh incompatibility is a condition that returns to your Rh status, a type of protein found on the surface of your red blood cells. The testing for this is particularly important during pregnancy. Doctors in the United States are encouraged to assess Rh blood type and any related antibodies in all pregnant women during their first prenatal visit.
This test may also need to be repeated between the 24th and 28th weeks of pregnancy, especially if you are an Rh-negative mother and your partner’s Rh type is not known or is Rh-positive. After you’ve given birth, it’ll be necessary to do the test again.
Depending on your test results, different courses of action may be taken:
If you’re Rh-positive, there’s no worry about Rh incompatibility regardless of the Rh status of your baby.
However, if you’re Rh-negative, further tests known as an antibody screen would be done to check for a condition known as alloimmunization – a reaction of your immune system if your baby is Rh-positive.
If you’re an Rh-negative mother and the antibody screen comes back positive, then a more specific test, called a Coombs test, would be necessary. This helps to guide how your pregnancy will be managed and monitored.
If you’re an Rh-negative mother and the result of your antibody test is negative, your partner’s Rh type could be checked. If they are also Rh-negative, then there’s no risk of Rh incompatibility and its associated problems. However, if your partner is Rh-positive, this increases the possibility of Rh incompatibility.
If your partner’s Rh type can’t be determined or they’re Rh-positive and you’re Rh-negative, then further testing would be needed to check if your baby’s blood has somehow mixed with yours – a condition called fetomaternal hemorrhage.
A screening test called a rosette test can be done to check for this. If the test comes back positive, then separate tests called the Kleihauer-Betke (KB) test or flow cytometry would be done to confirm the results and guide next steps.
In cases where you’re an Rh-negative mother that has previously been affected by Rh incompatibility, different ways would be used to monitor your baby during pregnancy. These include checking the speed of blood flow in your baby’s middle cerebral artery every 1-2 weeks starting from 24 weeks of pregnancy to directly assessing fetal blood counts (specifically hematocrit) through a procedure called cordocentesis if the blood flow speed is high. Tests to check the baby’s wellbeing (antenatal testing) would also be started from the 32nd week of your pregnancy.
Treatment Options for Rh Incompatibility
One of the main ways doctors manage Rh incompatibility, a condition where the mother’s immune system can potentially damage the child’s blood cells during pregnancy, is by preventing the mother from becoming sensitized. In simpler terms, they aim to stop her immune system from attacking the baby’s blood cells. They do this using Rh D immunoglobulin (RhIg), which is basically a medication made of anti-Rh D antibodies.
These antibodies specifically target and neutralize Rh-positive blood cells from the baby that may have entered the mother’s circulation, preventing her immune system from becoming sensitized.
RhIg has significantly reduced the occurrence of what’s known as alloimmunization, from 16% to less than 1%. Alloimmunization is when the mother’s immune system develops a defense against the Rh-positive cells of the baby, which can lead to complications.
In addition, RhIg use has also lowered the occurrence of Hemolytic Disease of the Newborn (HDN) to less than 1%. HDN is a condition where the mother’s immune system destroys the baby’s red blood cells resulting in severe anemia and jaundice in the baby.
So, if there’s a chance a mother could have Rh incompatibility during pregnancy, doctors will typically give prophylactic (preventive) RhIg to Rh-negative women who haven’t yet become sensitized at around 28 weeks into the pregnancy. If it’s then discovered after birth that the baby is Rh-positive, these same women are given another dose of RhIg within 72 hours of delivery.
The American College of Obstetricians and Gynecologists recommends all Rh-negative women who give birth to Rh-positive infants should have a screening test and if needed, another test to find out how many doses of the RhIg they need.
The same prevention strategy can be used for Rh-negative mothers who have had certain risky events during their pregnancy that might have let fetal blood enter their own circulation, a situation known as fetomaternal hemorrhage. The number of doses required differs depending on the situation and the stage of the pregnancy.
What else can Rh Incompatibility be?
When a physician is assessing a case of Rh incompatibility, various other medical conditions may appear similar and thus need to be ruled out. These include:
- Abo incompatibility
- Autoimmune hemolytic anemia
- Alpha thalassemia
- Chronic fetomaternal hemorrhage
- Erythroblastosis fetalis
- Hydrops fetalis
- Hereditary enzyme deficiencies
- Microangiopathic hemolytic anemia
- Spherocytosis
- Twin-twin transfusion
It’s important for the doctor to consider and rule out these conditions to reach an accurate diagnosis.
