The correct answer is Rh^(+) male marries Rh^(-) woman. Explanation & Key Takeaways: • When a male and female both are not either positive or negative for Rh factor, it's called Rh incompatibility. • If a woman who is Rh-negative and a man who is Rh positive conceive a baby, Rh incompatibility usually isn't a problem if it's the mother's first pregnancy. • That's because the baby's blood does not normally enter the mother's circulatory system during the pregnancy. • Rh antibodies may be harmful to the mother's second or later pregnancies. • If she is ever carrying another Rh-positive child, her Rh antibodies will recognize the Rh proteins on the surface of the baby's blood cells as foreign proteins. Her antibodies will pass into the baby's bloodstream and attack those cells. • This can make the baby's red blood cells swell and rupture. • This is known as hemolytic or Rh disease of the newborn. • It can make a baby's blood count very low. • This situation can be fatal to the second fetus. • Hence the correct answer is 'Rh-positive male marries Rh-negative woman'. Important Notes: • What is Rh Factor • An Rh factor is a protein found on some red blood cells (RBCs). • Not everyone carries this protein, though most do. • People who carry such protein are Rh-positive. • People who don't carry the protein are Rh-negative.