Prenatal Rhogam is an injection that is recommended at 28 weeks gestation to all women who have an Rh negative blood type by the medical model.

What is Rh negative blood?

Each person’s blood is one of four major types: A, B, AB, or O. Blood types are determined by the types of antigens on the blood cells. Antigens are proteins on the surface of blood cells that can cause a response from the immune system. The Rh factor is a type of protein on the surface of red blood cells. Most people who have the Rh factor are Rh-positive. Those who do not have the Rh factor are Rh-negative.

If you are Rh-negative, you may develop antibodies to an Rh-positive baby. If a small amount of the baby’s blood mixes with your blood, which is rare during pregnancy, your body may respond as if it were allergic to the baby. Your body may make antibodies to the Rh antigens in the baby’s blood. This means you have become sensitized and your antibodies can cross the placenta and attack your baby’s blood. They break down the fetus’s red blood cells and produce anemia (the blood has a low number of red blood cells). This condition is called hemolytic disease or hemolytic anemia. It can become severe enough to cause serious illness, brain damage, or even death in the fetus or newborn.

Any pregnancy event with the potential for fetal-maternal blood mixing can sensitize the mother. The chances of mixing and sensitization are lower earlier in pregnancy, but there’s still a risk. Sensitization can occur if an Rh negative woman has had:

  • Undetected capillary separation of the placental bed due to increased blood volume (maximal blood volume expansion occurs at 28 weeks gestation)
  • A fall or car accident that causes trauma
  • An ectopic pregnancy
  • Chorionic villus sampling
  • Amniocentesis
  • A blood transfusion
  • A miscarriage


How am I tested for Rh negative blood or Rh sensitization?

Blood typing and sensitization testing are part of the routine Prenatal Lab Profile offered at the beginning of care.  Repeat sensitization testing is offered to Rh negative women at additional intervals throughout the pregnancy and immediate postpartum.

Is there treatment for Rh sensitization?

There is no easy treatment for Rh sensitization.  In a first pregnancy any sensitization will likely be small, it is future pregnancies where the increased amount of antibodies are most likely to cause damage to fetal blood cells.  There are treatments both for fetal blood damage both during pregnancy and immediately after birth, but they are not considered safe and effective enough to avoid intense sensitization prevention efforts.

How can I prevent Rh sensitization?

Most doctors recommend an injection of Rh antibodies (widely known by the trade name RhoGAM) at 28 weeks to head-off sensitization, as well as after birth. The exact mechanism by which this injection works is not known. RhoGAM doesn’t attack the fetus’s blood because there are different kinds of antibodies and the ones in RhoGAM are a type that won’t cross the placenta.

Prenatal Rhogam is considered controversial as it is unclear how much protection the injection provides.  The shot is recommended at 28 weeks due to increased blood volume creating undetected capillary separation of the placental bed that could lead to fetal-maternal blood mixing.  It is unclear, however, just how long this injection provides protection.  Prior to 2002, the Rhogam injection contained the preservative Thimerosal (mercury), which has been linked to certain types of autism in children.  Rhogam in now available without mercury, but it still contains preservatives that may have effects on the fetus or pregnant mother.

The trade name for the injection of mercury-free Rh antibodies is Rhophylac. Warnings and precautions listed in the package insert for this product are:

  • Allergic or hypersensitivity reactions, including anaphylactic shock
  • Exposure to viruses and other infectious agents that cannot be fully screened from this human blood product
  • Adverse reactions to the shot can include nausea, dizziness, headache, injection site pain, and malaise

The manufacturers also state that clinical trials have only been conducted on the efficacy (how well it works) and not on the safety of this product in pregnancy.

Are there other ways to prevent sensitization in pregnancy?

The best way to avoid sensitization caused from placental separation is to have established a healthy placental bed. The health of the uterine wall at the time of implantation and the continuing health of placental tissues during its formation in the first 12 weeks of pregnancy can help it withstand the pressures of increased blood volume later in the pregnancy.  This is primarily controlled through good nutrition in the childbearing cycle.

Drinking Red Raspberry Leaf tea is beneficial throughout the second half of pregnancy. It helps tone the uterus for labor. This will help keep blood loss at a minimum during and after birth. Drinking citrus juices and selecting vitamin C rich foods is believed to help keep the placenta strong and healthy.

Eliminating fluoridated water is also recommended as fluoride has been shown to interfere with collagen production. Collagen is what holds the placenta firmly attached to the uterus.

Information compiled from the following sources:

Rh Immune Globulin & Citrus Bioflavonoids: When to Use Them by Rebecca Lessard
American Pregnancy Association
Prenatal Rhogam:  Examining Reality by Kristen Hart

More information about Rhogam

RhoGAM Shot During Pregnancy