Final answer:
A pregnant woman should be concerned about hemolytic disease of the newborn if she is Rh-negative and the father is Rh-positive, primarily during her second or subsequent pregnancies, as the maternal antibodies formed during an earlier pregnancy can harm an Rh-positive fetus.
Step-by-step explanation:
Hemolytic Disease of the Newborn and the Rh Factor
A pregnant woman needs to be concerned about her fetus developing hemolytic disease of the newborn (HDN) only if she is Rh-negative (Rh-) and the father is Rh-positive (Rh+), particularly in her second or subsequent pregnancies. During the first pregnancy with an Rh+ fetus, sensitization may occur when fetal blood cells enter the mother's bloodstream, prompting her immune system to produce anti-Rh antibodies. However, it is usually during a second pregnancy with an Rh+ fetus when these previously formed maternal anti-Rh antibodies can cross the placenta, potentially leading to HDN by causing agglutination and destruction of the fetal red blood cells. This risk can be mitigated with the administration of Rho(D) immune globulin during the first pregnancy.
Hemolytic disease is more probable in second or subsequent pregnancies because the mother's immune system has already been sensitized and has produced antibodies during the first pregnancy. Hence, if an Rh- woman is pregnant, and especially if the father is Rh+, it is critical for her to receive proper prenatal care to monitor and prevent HDN.