Human Papillomavirus, or HPV, is a viral pathogen that most commonly spreads through sexual contact. HPV strains 6 and 11 normally cause genital warts, while HPV strains 16 and 18 commonly cause cervical cancer, which causes cancerous cells to spread in the cervix. Physicians can detect those HPV strains, using a Pap smear, which is a diagnostic test that collects cells from the female cervix.

Rh factor is a protein found on the outside of Rh-positive red blood cells. Rh incompatibility during pregnancy occurs when an Rh-negative mother is pregnant with an Rh-positive fetus. During delivery, the fetus' Rh-positive blood is introduced into the mother’s body. The Rh-negative mother’s body begins to produce antibodies that attack and kill Rh-positive blood cells. Since the crossover of blood normally occurs during delivery, an Rh-negative woman’s first pregnancy is normally not affected. However, the woman’s antibodies may attack a second Rh-positive fetus as those antibodies can cross into the bloodstream and destroy fetal Rh-positive blood cells.