Rh factor

The Rhesus blood group system (Rh blood group system) [which includes the Rh factor] is one of the 35 existing human blood group systems, and is considered as the 2nd most important blood group system.

Each individual’s blood is one of 4 major blood types A, B, AB, and O. Blood types are determined by the types of antigens [which trigger the response from the immune system] found on the surface of the red blood cells.


At the present time, the Rh blood group system comprises of 50 blood – group antigens such as the most immunogenic antigens D, C, c, and E. By which, the widely used terms Rh factor [which comprise of negative and positive] only refer to the D antigen only.

The Rhesus factor

The Rhesus factor (widely known as Rh factor), or the D antigen of the Rh blood group, system is an inherited protein carried by red blood cells (RBCs).

This type of immunogenic antigen determines the possibility of Hemolytic disease of the fetus and newborn (HDN, HDFN) [erythroblastosis fetalis in medical terms].

The Rhesus blood type is named after a rhesus macaque (a type of monkey) which was discovered in 1937 by Alexander S. Wiener and Karl Landsteiner.

Pregnancy week by week

The importance of the discovery was later realized in 1940 by Philip Levine and Rufus Stetson. The discovered serum was produced via immunization of animals using red blood cells.

In 1942, medical practitioners and scientists started to use Rh factor for antigens and anti – Rh for antibodies. The usage was established in 1963 using what they now call the Rh factor.

The Rh factor test

Every mother – to – be must take the Rh factor test, it is considered as one of the 1st and most essential test she will have during the journey. With that being said, below are the step – by – step procedure on how this outpatient procedure is performed:

  1. A medical practitioner will let a mother – to – be sit or lie in a comfortable position.
  2. Then a blood sample is taken.

The Rh factor test is only done once during gestation. This type of blood test is also harmless for both the mother and the baby. As a matter of fact, the innovation of screening and blood tests lessen the cases of Rh fetal diseases.

The Rh factor test results

The Rh factor test is recommended to take during a mother – to – be’s prenatal visit. As part of the pre – natal care, she will have blood tests to find out her blood type. In some cases, the father [might] need to take this test as well.

With that being said, an individual will also be able to know if he is:

Rh negative

Rh negative is the lack of Rh antigen, although being in this blood group does not equate to being ill and does not affect one’s health. However, this is what individuals need to expect if he belongs in this blood group:

  • Rh negative mothers [might] need to take another blood test and an antibody screen during the 1st trimester and repeated in the 28th week of pregnancy. In line with this, an antibody screen is a similar to Rh factor test which also determines if an Rh negative person has already developed Rh antibodies
  • Rh negative parents cannot reproduce an Rh positive offspring. This in turn will not mobilize the mother’s immune system to see the fetus as a foreign organism

Rh positive

Rh positive is when the blood has an ample amount of antigens, and having this does not affect an individual’s well – being. It is the most common blood type and about 85% of the population belongs in this blood group.

Here are the things to expect if a person is Rh positive:

  • Rh incompatibility is not a concern. This is because either the fetus is Rh positive or negative, there are no foreign antigens on the fetus’s red blood cells to cause the mother’s immune system to counteract

Rh sensitized

Sensitization refers to the fetus’s blood mixing up with the mother’s blood. This in turn triggers the mother’s body to respond as if it were allergic to the fetus.

Rh sensitized refers to a woman who has produced protein with Rh antibodies. These antibodies are not a problem in the current pregnancy. However, it will be a great concern in the future pregnancy.

An Rh sensitized mother will undergo the following medical procedures:

  • Diagnostic testing for maternal – fetal medicine
  • Neonatal blood transfusion to replace the sickly blood cells with fresh and healthy ones

Severe Rh sensitized

For severe Rh sensitized cases, enlisted below are the medical procedures that should be performed:

  • Labor induction
  • Intrauterine fetal blood transfusion for Rh disease

Rh incompatibility

Rh incompatibility refers to parents with opposing Rh factors such as the following situations below:

Mother is Rh negative and the father is Rh positive

If the mother is Rh negative while the father has the opposite Rh factor, the fetus will likely inherit the Rh factor of the father. Unfortunately, complications arise if the fetus has the Rh factor and the mother does not.

Rh negative mother carrying an Rh positive baby

If an Rh negative mother carries an Rh positive baby, the mother will produce proteins with Rh antibodies to damage the fetus’s red blood cells (Rh incompatible pregnancy).

In line with this, the mother’s antibodies will intrude the placenta and attack the fetus’s blood. This in turn breaks down the fetal red blood cells which results to the development of hemolytic anemia.

Hemolytic anemia is a life – threatening condition where a person lacks red blood cells.

If hemolytic anemia becomes severe, it may lead to serious illnesses, brain damage, and even stillbirth.

Preventative measures and treatment options

Dealing with either Rh negative or positive results has a lot of preventative measures and treatment options available. Enlisted below are the ways individuals can consider taking:

Blood test

A blood test basically provides an individual with his blood type (including the Rh factor).

Antibody screen

Antibody screen is another type of blood test. It is used to determine if an Rh negative mother has developed antibodies to an Rh positive blood.

Rh immunoglobulin injection

Rh – d immunoglobulin/ immune globulin (RhIg) injection is a blood product which prevents the sensitization of an Rh negative mother – to – be. Immune globulin prevents the body from producing Rh antibodies during gestation.

RhIg is used during the course of gestation and right after childbirth with the following situations:

Rh positive

  • For Rh positive newborns, the medical practitioner will give another dose of RhIg before and during the course of childbirth. This is to prevent the intrusion of antibodies to the Rh positive cells
  • For pregnancy and delivery of an Rh positive baby, repeated doses of RhIg is good for the given pregnancy

Rh negative

  • Rh negative mother has not been sensitized yet. The medical practitioner will give RhIg around the 28th week of pregnancy
  • Plus, they [rh negative mothers] can still receive RhIg even after they experienced miscarriage, ectopic pregnancy, induced abortion to hinder the development of antibodies that would intrude the future Rh positive baby
  • Rh negative newborns do not need [any] additional treatment

Mother is Rh negative and baby is Rh positive

In a situation where the mother is Rh negative and the baby is Rh positive, the mother needs to have a RhIg injection even after any of the following situations:

  • Miscarriage and/or self – induced miscarriage
  • Abortion
  • Ectopic pregnancy
  • Molar pregnancy
  • Amniocentesis
  • Chorionic Villus sampling (CVS)
  • Bleeding during pregnancy
  • Abdominal trauma during pregnancy
  • Breech presentation position
  • Fetal blood sampling (FBS)
  • Blood transfusion
  • Menstrual extraction

After tubal ligation

Tubal ligation (also called as tubectomy) refers to a surgical procedure which involves tying the fallopian tubes to prevent future pregnancies. A mother who underwent tubal ligation may still receive RhIg due to the following reasons:

  • To reverse sterilization in the future
  • A dwindling chance that sterilization may fail to prevent a future pregnancy
  • In case of needing future blood transfusions, RhIg will prevent the development of antibodies

Future pregnancy

If a woman gets pregnant again, she is required to take further RhIg injections.

Vaginal spotting during pregnancy

If a mother – to – be experiences vaginal spotting (also called as vaginal bleeding) while gestating, a medical practitioner will also recommend injecting Rh immune globulin.

Rh incompatibility treatment

Rh incompatibility treatment (RhoGAM) is performed to prevent the development of Rh antibodies to protect the fetus.

This type of treatment is done in couples with opposing Rh factors. This is because an Rh negative mother needs extra special care during the gestating period.

With that being said, RhoGAM is administered in the following ways:

For Rh negative

  • Rh negative individuals will be given RhoGAM via a vaccine – like injection into the muscle tissue of the arm or backside. The injection can cause a level of pain and can become sore for a couple of days. In line with this, RhoGAM can also be administered after any genetic testing such as chorionic villus sampling and amniocentesis
  • If the newborn is Rh negative, no further treatment is required.

For Rh positive

  • If a newborn is Rh positive, an additional dose is administered within 72 hours after child delivery if blood test

If left untreated, Rh incompatibility will lead to fetal Rh disease.


Amniocentesis is for Rh negative mothers who did not took RhoGAM treatment during her previous pregnancy, and test results show that she is already Rh sensitized.

This type of treatment is used to check the fetus’s blood type and antibody levels will be checked regularly.

Ultrasound test

If the antibody levels become seriously high, she must take an ultrasound test for fetal assessment purposes.

Rh negative blood transfusion

Transfusion of Rh negative blood is necessary if the fetus’s life is threatened because he is affected with hemolytic anemia and/or fetal Rh disease.

Rh negative blood transfusion is done after child delivery or sometimes while the baby is still inside the womb.