Final answer:
Finasteride can be transmitted through semen and has the potential to cause birth defects in the fetus, particularly affecting male genital development, thus it is advised not to be used by those trying to conceive.
Step-by-step explanation:
Finasteride, primarily used for the treatment of male pattern hair loss, should not be used when trying to conceive as it can be transmitted through the semen and may harm the fetus. Ingestion of finasteride by pregnant women can potentially cause birth defects, particularly to the male fetus, often affecting the development of genitalia. It is important to note that while finasteride may not affect sperm count or obstruct reproductive tubes, its presence in semen can pose risks to fetal development.