In Greek mythology, Queen Niobe’s pride led to her children’s death, and her endless grief turned her into stone. The human body, too, can be undone by its own devotion: A mother’s immune system may one day harden against her child. A simple genetic mismatch can trigger a dangerous immune response when a pregnant parent with Rh-negative blood carries a baby whose blood is Rh-positive. This condition, known as Rh incompatibility, remains one of the most preventable causes of fetal and newborn mortality worldwide.

The Rh factor is a small protein found on the surface of red blood cells. If you have the protein, you’re Rh-positive; if you don’t, you’re Rh-negative. When even a trace of Rh-positive blood from a fetus enters the circulation of an Rh-negative parent during pregnancy, her immune system may recognize those Rh-tagged red blood cells as foreign and begin producing antibodies against them. This process, called Rh sensitization, could happen during childbirth, miscarriage or a medical procedure. It rarely causes harm during a first pregnancy but can lead to devastating complications in later ones.

In a subsequent pregnancy, the mother still has these antibodies from earlier. If they cross the placenta, they can attack and destroy the red blood cells of an Rh-positive fetus or newborn baby. The baby can develop severe anemia, jaundice, heart failure or may even die.

Fortunately, modern medicine has made prevention of possible tragedy simple and highly effective. Every pregnant person’s blood type is tested early in their prenatal care. Someone who is Rh-negative will receive an injection of Rh immunoglobulin (called anti-D or RhoGAM). This medication clears fetal Rh-positive cells from the parent’s bloodstream before the immune system reacts to them. If the baby is Rh-positive, the parent will get an injection around the 28th week of pregnancy and again within 72 hours after birth. The treatment prevents the mother’s body from reacting to Rh-positive blood and protects future pregnancies.

Knowledge turns tragedy into prevention. Knowing your blood type, going to regular prenatal visits and receiving anti-D when needed are simple but life-saving acts. With modern care, what once was a story of grief has become one of protection.