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Rh Factor and Pregnancy


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The Rh factor is a characteristic of the blood. One reason to have a blood test early in pregnancy is to check your blood type and see if your blood has the Rh factor. Blood types are named with letters and either “positive” or “negative.” For example, some blood types are AB positive and others are O negative. The “positive” or “negative” refers to the Rh factor. If a person has the Rh factor, he or she is Rh positive. People who do not have it are Rh negative.

Most of the time, the Rh factor has no effect on a person’s health. Sometimes, though, it can harm a developing baby.

Women who are Rh positive do not have problems with the Rh factor in pregnancy.

If you are an Rh negative woman and are pregnant, it is vital that a doctor, nurse, or midwife watch your pregnancy closely. If your developing baby is also Rh negative, there is no danger. But if your baby is Rh positive, he or she may have health problems.

Blood cells from an Rh positive baby can enter the Rh negative mother’s bloodstream. The mother’s body responds to these cells by making antibodies. Antibodies are made by the body to protect it from disease and other “foreign” substances. The mother’s antibodies can attack and damage the baby’s blood cells. This can cause the baby to have anemia or jaundice (yellow color of skin). In severe cases, the antibodies may cause stillbirth.

Since it takes some time for these antibodies to form, Rh factor is rarely a problem for a woman’s first baby. Without treatment, however, her future babies are at high risk.

The RhoGAM vaccine can prevent this problem. The vaccine prevents the mother’s body from producing antibodies to Rh positive blood cells. It also protects any baby that she may have in the future. This is why prenatal care is so important.

A woman with Rh negative blood must receive the RhoGAM vaccine during her first pregnancy to prevent future problems. Once a woman has produced antibodies, the vaccine will not work.

Under the doctor’s supervision, the vaccine is given around the 28th week of pregnancy. The vaccine also is given within 72 hours:

  • After any vaginal bleeding during pregnancy
  • After the prenatal tests chorionic (ko-ree-ON-ic) villus sampling and amniocentesis (AM-nee-o-sen-TEE-siss)
  • After a miscarriage or stillbirth
  • After the baby’s birth

The vaccine may prevent the woman’s body from producing antibodies to Rh  positive blood cells, and may protect any baby that she may have in the future.

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