A pregnant woman needs to be concerned about her fetus developing hemolytic disease of the newborn only if the woman is Rh and the father is Rh .

A pregnant woman needs to be concerned about her fetus developing hemolytic disease of the newborn only if the woman is Rh negative and the father is Rh positive.

Here are the steps:

1. The Rh factor is a type of protein on the surface of red blood cells. Most people are Rh positive. Those who do not have the Rh factor are Rh negative.

2. If you're Rh negative and the baby's father is Rh positive, the baby may inherit the father's Rh-positive blood type.

3. Your Rh-negative blood could develop antibodies to the Rh-positive blood. This is known as Rh sensitization and it can occur when an Rh-negative woman is pregnant with an Rh-positive baby and the baby's blood enters the mother's bloodstream.

4. If Rh sensitization occurs, the mother's body will produce antibodies that can destroy the baby's red blood cells. This can lead to hemolytic disease of the newborn, which can cause serious illness, brain damage, or even death in a newborn.

5. However, Rh sensitization is preventable with a medicine called Rh immunoglobulin, which can prevent the mother's body from producing Rh antibodies. This medicine is typically given during the 28th week of pregnancy and within 72 hours after birth if the baby is Rh positive.

6. Therefore, it's important for all pregnant women to have a blood test to determine their Rh factor. If the mother is Rh negative and the father is Rh positive, the doctor will likely recommend treatment with Rh immunoglobulin to prevent Rh sensitization.