What is Rh Incompatibility?

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  • Written By: wiseGEEK Writer
  • Edited By: O. Wallace
  • Last Modified Date: 13 October 2019
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Rh incompatibility results when a pregnant mother with a negative blood type is carrying a child with a positive blood type. This can be a serious risk of health to the unborn child, since the mother’s body may react to the child’s blood type by producing antibodies against it. Rh incompatibility only occurs when the mother is negative blood type and the child positive. A woman with a positive blood type who has a baby with a negative blood type is not at risk for this condition.

In most cases, having a first child where incompatibility exists hazards no risk to the infant. It is usually the second child with the incompatibility that is at greatest risk. Normally, a woman is treated in her first pregnancy where Rh incompatibility exists, by immunizing her against developing positive blood type antibodies. Usually a woman receives one gamma globulin shot at the 28th week of pregnancy and another within three days after giving birth. This tends to prevent Rh incompatibility in future pregnancies.


A woman does not need to carry a baby to term in order to develop incompatibility in future pregnancies. If a woman is pregnant and miscarries, she is usually given the same “vaccine” in order not to risk the health of future children. Sometimes, a woman may not know the history of previous children and whether she might have carried a baby that produced Rh incompatibility. If she has a negative blood type and has had a previous pregnancy with a father whose blood type is not known, the best method of determining the potential presence of the condition is testing the child’s blood type. If the child has a positive blood type, it can be assumed the woman will develop Rh incompatibility with other children, if her partner has a positive blood type.

When incompatibility is not addressed, which may be a problem for women who don’t receive prenatal care, the effects on the newborn can be very grave. A child with incompatible blood can be born with brain damage, jaundice, and in more severe cases, born in heart failure. Further, some children die at birth or shortly thereafter when Rh incompatibility is not detected.

When women receive prenatal care, they are almost always blood type tested in order to determine if there is a risk of Rh incompatibility. It used to be standard practice in the US to require a blood test prior to marriage in order to be prepared for babies that might be at risk for this condition. Few states still make this requirement, but if you are planning on getting pregnant, married or not, you should definitely be sure to have both your and your partner’s blood tested. Again, if the mother has positive blood, there is no need to test the father.


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Post 2

Is an O positve girl compatible with an O negative boy? In case of a married couple, will it affect pregnancy in any manner?

Post 1

what if the father is Rh negative and the mother is Rh positve?

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