Both the male and female reproductive systems play a role in pregnancy. Problems with these systems can affect fertility and the ability to have children. Something that affects reproductive health is called a reproductive hazard. Examples include:

• Radiation
• Metals such as lead and mercury
• Chemicals such as pesticides
• Cigarettes
• Some viruses
• Alcohol

For men, a reproductive hazard can affect the sperm. For a woman, a reproductive hazard can cause different effects during pregnancy, depending on when she is exposed. During the first 3 months of pregnancy, it might cause a birth defect or a miscarriage. During the last 6 months of pregnancy, it could slow the growth of the fetus, affect the development of its brain, or cause premature labor.