What is the Rhesus Factor?

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The Rhesus factor, also known as the Rh factor, gets its name from experiments conducted in 1937 by scientists Karl Landsteiner and Alexander S. Weiner. These revolutionary case studies involved rabbits which, when injected with the Rhesus monkey's red blood cells, produced an antibody present in the red blood cells of many humans--the Rhesus factor. The Rhesus factor is an antigen, or more specifically a protein, that exists on the surface of red blood cells.

There are four general categories of blood: A, B, O, and AB. But each blood type is further labeled as positive or negative which is a reference to the Rhesus factor of the blood. People with the Rhesus factor, that is, people with the antigen present in their blood, are Rh-positive. So if a person has a blood type of A and has the Rhesus factor, she is A-positive, or A+. More than 85% of people are Rh-positive. People without the Rhesus factor, that is, people that don't have the antigen in their blood, are Rh-negative.

A person's Rh type is basically significant only with respect to pregnancies. Specifically, a Rh-positive child born to an Rh-negative woman runs the risk of developing Rh disease. Only Rh-negative women risk having children with the Rhesus factor disease; Rh-positive women do not. So, for a Rh-negative woman to have a Rh-positive child, the father must have been Rh-positive. A Rh-positive man has a 50% chance of passing on his Rh-positive blood type to the child.

If the mother is Rh-negative and the child is Rh-positive, and the child's blood enters the woman's bloodstream during the pregnancy, labor, or delivery, the woman's immune system may respond by producing antibodies to fight off the child's antigens which are foreign to the woman's system. That is, the woman's body may naturally produce antibodies which attack the baby's blood, causing the baby's red blood cells to break down. The result of this incompatibility will not affect the health of the mother but it can affect the child's health. Potential health problems include jaundice, anemia, brain or heart damage, and in severe cases Rh disease can be fatal.

The Rhesus factor is less likely to affect the first-born child because the woman's system will have had less time and is therefore less likely to produce the antibodies to fight off the antigens in the child's Rh-positive blood. If the woman has become sensitized, that is, her immune system responded by producing antibodies, those antibodies will be present in her system for the rest of her life. Therefore, disparate Rhesus factor types between a woman and her child can increase the potential for Rh disease in each subsequent pregnancy.

Preventative measures to protect against the Rhesus factor disease and their devastating effects are available. Women should be tested early in their first pregnancies to determine whether they are Rh-negative and whether they are sensitized. Sensitization may not only occur through normal pregnancies, but at any time a woman and her child's blood mix, including miscarriages, ectopic pregnancies, and blood transfusions.

If a woman is Rh-negative, and has not yet been sensitized, she will likely be given an injection of a blood product known as Rh immunoglobulin (Rhlg) at about seven months into the pregnancy. This should prevent sensitization for the rest of the pregnancy. The Rhlg shot seeks to destroy any antigens present in the bloodstream before the mother is able to create antibodies. Additionally, it is generally recommended that the newborn be tested for his or her Rhesus blood type. If the child is positive, the mother is often given another Rhlg shot shortly after birth to prevent her from becoming sensitized. Rhlg injections only last for a given pregnancy. Subsequent pregnancies will likely require separate Rhlg injections.

If the woman is Rh-negative and has been sensitized, the Rhlg injection will not help. Close monitoring of the baby should be conducted to ensure that Rh disease is not developing. Blood transfusions to replace the diseased blood with healthy blood may be given during or after delivery depending on the circumstances.

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Discuss this Article

i'm rh negative & my husband rh positive. our first baby died; a newborn. it was rh positive. it died of a lung hemorrhage. kindly inform me if the rh factor could be a danger for the next baby. precautions recommended.
- avie
Is it possible for a couple, both of whom are Rh+ to have Rh- child?

Thanks

- premahuja
I have B negative bld grp and very soon going to marry. She has A positive bld grp. Plz tell me will there b any complication in our child?
- satishpgoyal
What if the woman is rh+ and the man rh-, what is the result of their children?

- anon25317
I am O+. After I delivered my third baby, I was told that my body produced antibodies (anti-c)! Which was odd. How is that possible?
- anon22904
Hi can anyone help? if my wife is rh o- and i am ab + is it possible to father a child with a- blood

thanks m ...

- markc
is it possible to change my blood type from ab+ to ab-? if so, how?
- danielfarina
Can a RH-negative father and a RH-positive mother bear children without complications?
- anon16055
I am A+, my husbands blood switches between + & -. When my son was born they had to test his blood many times and finally determined that he is a positive donor but a negative receiver. What causes this? Is it likely to cause him any problems?
- Kris3065
My daughter is 0- and her husband is +. She had a miscarriage about a year ago and didn't know that she should have been checked for antibodies. She is now pregnant and everything looks good, but the doctor does not want to see her until her 8 to 10 week check-up. Should she insist on being seen earlier and what are the chances that she became sensitive? Her miscarriage was @ 4 to 6 weeks.
- momma303
There are numerous factors in calculating blood types and unfortunately we can't provide that service here on wiseGEEK. But, if you input "blood type calculator" into your search engine, several easy-to-use choices come up!
- olivia
Here are the possibilities:

If one parent is Rh positive and the other is Rh negative, the child could be either Rh positive or Rh negative. The only way to know is to test the child's blood type.

If both parents are Rh negative, the child will necessarily be Rh negative.

If both parents are Rh positive, the child could be either Rh positive or Rh negative. This is because people have two alleles going to their Rhesus factor. Rh positive people can have two Rh positive alleles, or one positive and one negative while still being classified as positive. If at least one of the positive parents has a negative allele then that negative factor can be passed on to the child. A Rh negative person, on the other hand, necessarily has two Rh negative alleles.

- malena
Can a mother with O- blood and a father with A positive have an O+ child? in school I was told this is not possible- is this true?
- justd2006
Can two O+ parents have an O- child?
- Shayna
can a woman with A1 positive marry a man with O negative? will she face any problems with during the pregnancy???
- renukrs
can a lady who is O negative and shorteye sighted marry a man who is o positive and also short sighted.

what is/are the possible effect on their children?

is it advicale for them to get married?

- anon1382
Yep, that is certainly possible. If the father's blood type is AO+- (which would appear as an A+), he could give the O- to his child, who would also receive an O- from the mother. The only way to have an O- blood type is OO--.
- Dayton
If the mother is O- and the father is A+, is it possible to have a child with O-?
- anon1337
Interestingly enough, that IS possible. Essentially, one parent would have to be AO+- (which would appear as A+), and the other BO+- (which would appear as B+). The child could receive an O and an - from each parent.

Genetics at work!

- Dayton
If one person has A positive blood and the other has B positive blood, is it possible for their children to have O negative blood.
- schu

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