Definition

Rh factor is a protein that may be found on the surface of red blood cells. If you carry this protein, your blood is Rh positive. If you don’t carry this protein, your blood is Rh negative.

Sometimes a mother with Rh-negative blood is pregnant with a baby that has Rh-positive blood. This can cause a problem if the baby’s blood enters the mother’s blood flow. The Rh-positive blood from the baby will make the mother’s body create antibodies. This is called isoimmunization. The antibodies will attack any Rh-positive blood cells. This will not cause a problem for the mother. However, the antibodies can pass to the developing baby and destroy some of the baby’s blood cells.

Fortunately, Rh incompatibility is often prevented with an immunization. If the condition is not prevented, the baby may need care.

Causes

A baby’s Rh status is determined from the mother and father. If the mother is Rh negative and the father is Rh positive, the baby has at least a 50% chance of being Rh positive. However, Rh isoimmunization will only happen if the baby’s Rh-positive blood enters the mother’s blood flow. In most pregnancies, the mother’s and baby’s blood will not mix. The baby’s blood may come into contact with the mother’s blood flow during:

• Miscarriage
• Induced abortion
• Ectopic pregnancy
• Trauma during pregnancy
• Amniocentesis or other invasive testing procedures related to pregnancy—rare

The mix in blood happens most often at the end of pregnancy. This means it is rarely a problem in a woman’s first pregnancy. The mother’s antibodies could affect a future pregnancy with a baby with Rh-positive blood even if the blood is not mixed.

A woman can also become sensitized to Rh-positive blood if she receives an incompatible blood transfusion.

Risk Factors

Factors that put you at risk for Rh incompatibility include being an Rh-negative pregnant woman who:

• Had a prior pregnancy with a baby that was Rh positive
• Had a prior blood transfusion or amniocentesis
• Did not receive Rh immunization prophylaxis during a prior pregnancy with an Rh-positive baby

Symptoms

Symptoms and complications will only affect the baby. The complications occur when standard preventive measures are not taken. The symptoms can vary from mild to severe.

Symptoms that can develop in the baby include:

• Swelling of the body, which may be associated with heart failure or respiratory problems.
• Jaundice
• Anemia

A complication of untreated jaundice is kernicterus, a syndrome which can affect the baby’s nervous system. Contact your doctor right away if your baby:

• Has a yellow or orange appearance to the skin
• Does not sleep
• Is hard to wake up
• Is not breastfeeding or has difficulty sucking from a bottle
• Is restless or fussy

Call for emergency medical help if your baby has:

• High pitched crying or crying that won’t stop
• A bowed body
• A stiff, limp, or floppy body
• Strange eye movements

Diagnosis

You cannot detect Rh incompatibility on your own. A blood test can determine whether you are Rh positive or Rh negative. The blood test will also look for Rh antibodies or monitor the levels of antibodies through pregnancy. If the antibody levels are high, an amniocentesis can determine if the fetus is ill.

It is important to have a blood test at the beginning of pregnancy.

Treatment

Rh incompatibility is almost completely preventable using immunization. The best treatment is prevention.

If Rh incompatibility does occur, then the baby may need treatment based on symptoms such as:

Prevention

If a mother is at risk for Rh incompatibility, then an injection of Rho immune globulin will be given at week 28 of the pregnancy. A second injection will be given within 72 hours after delivery. These injections will block the mother’s body from developing antibodies. Women at risk may also be given these injections after a miscarriage, induced abortion, or ectopic pregnancy. These injections will protect the current pregnancy and future pregnancies.

Routine prenatal care should help identify, manage, and treat any complications of Rh incompatibility.

American Pregnancy Association http://www.americanpregnancy.org/

Women’s Health Matters http://www.womenshealthmatters.ca

Jaundice and kernicterus. Centers for Disease Control and Prevention website. Available at:
http://www.cdc.gov/ncbddd/jaundice/facts.html
Updated June 27, 2013. Accessed March 18, 2014.

Rh factor. American Pregnancy Association website. Available at:
http://americanpregnancy.org/pregnancy-complications/rh-factor
Updated April 2006. Accessed March 18, 2014.