One of the first tests performed at the beginning of a pregnancy is blood-type. This basic test determines your blood type and Rh factor. People with different blood types have proteins specific to that blood type on the surfaces of their red blood cells.

There are four blood types (A, B, AB, and O). Each of the four blood types is additionally classified according to the presence of another protein on the surface of red blood cells that indicates your Rh factor. If you carry this protein, you are Rh positive. If you don't carry the protein, you are Rh negative.

Most people—about 85%—are Rh positive. But if a woman who is Rh negative and a man who is Rh positive conceive a baby, there is the potential for incompatibility. The baby growing inside the Rh-negative mother may have Rh-positive blood, inherited from the father. Statistically, at least 50% of the children born to an Rh-negative mother and Rh-positive father will be Rh positive.

Causes

Rh incompatibility occurs when a woman is Rh negative, but her fetus has inherited Rh-positive blood from the father. It rarely occurs in a woman's first pregnancy. She only becomes sensitized to the fetus's Rh-positive blood once she comes in contact with it. This is usually not until very late in pregnancy or during childbirth. This can also occur during a miscarriage or if the fetus is aborted. In rare cases, it can happen during an amniocentesis or other invasive procedures related to pregnancy.

A woman can also become sensitized to Rh-positive blood if she receives an incompatible blood transfusion. In most cases of Rh incompatibility, there are not disease manifestations. If maternal antibodies develop against Rh-positive proteins, then these antibodies could affect a current or future fetus during pregnancy. This is called Rh isoimmunization.

Risk Factors

A risk factor is something that increases your chance of getting a disease or condition. Risk factors include:

• Being a pregnant woman with Rh-negative blood who had a prior pregnancy with a fetus that was Rh positive

• Being a pregnant woman who had a prior blood transfusion or amniocentesis

• Being a pregnant woman with Rh-negative blood who did not receive Rh immunization during a prior pregnancy

Symptoms

Symptoms and complications only affect the fetus and/or newborn. They occur when standard preventive measures are not taken and can vary from mild to very serious. The mother's health is not affected.

Symptoms of the newborn baby include:

• Anemia

• Swelling of the body, which may be associated with:

• • Heart failure

• • Respiratory problems

• This condition is also referred to a hydrops fetalis.

• Kernicterus (a neurological syndrome), which can occurs in stages:

• • Early:

• • • High bilirubin level (greater than 18 mg/cc)

• • • Extreme jaundice

• • • Absent moro (startle) reflex

• • • Poor suck

• • • Lethargy

• • Intermediate:

• • • High-pitched cry

• • • Arched back with neck hyperextended backwards (opisthotonos)

• • • Bulging fontanel (soft spot)

• • • Seizures

• • Late:

• • • High-pitched hearing loss

• • • Mental retardation

• • • Muscle rigidity

• • • Speech difficulties

• • • Seizures

• • • Movement disorder

Diagnosis

There aren't any physical symptoms that would allow you to detect on your own if you are Rh incompatible with any given pregnancy. If you are pregnant, it is standard procedure for your healthcare provider to order a blood test that will determine whether you are Rh positive or Rh negative. If the blood test indicates that you have developed Rh antibodies, your blood will be monitored regularly to assess the level of antibodies it contains. If the levels are high, an amniocentesis would be recommended to determine the degree of impact on the fetus.

Treatment

Since Rh incompatibility is almost completely preventable with the use of immunization (immune globulin injection of RhoGAM), prevention remains the best treatment.

Prevention

Rh incompatibility is almost completely preventable. Rh-negative mothers should be followed closely by their obstetricians during pregnancy. If the father of the infant is Rh-positive, the mother is given a mid-term injection of RhoGAM and a second injection within a few days of delivery. These injections prevent the development of antibodies against Rh-positive blood. This effectively prevents the condition. Routine prenatal care should help identify, manage, and treat any complications of Rh incompatibility.

RESOURCES:

American College of Obstetricians and Gynecologists
http://www.acog.org

March of Dimes Birth Defects Foundation
http://www.modimes.org

References:

March of Dimes Birth Defects Foundation website. Available at: http://www.modimes.org.

Medline Plus website. Available at: http://www.nlm.nih.gov/medlineplus/ency/article/001600.htm#Prevention.

The Merck Manual of Medical Information—Home Edition. Simon and Schuster, Inc.; 2000.

US National Library of Medicine website. Available at: http://www.nlm.nih.gov/.