Which reproductive toxin is known to cause birth defects without noticeable harm to the parent?

The term that describes a substance capable of causing birth defects without causing noticeable harm to the parent is a teratogen. Teratogens can affect the development of an embryo or fetus, leading to malformations or developmental issues. Importantly, teratogens can produce these effects even if the parent does not exhibit any symptoms of toxicity or other adverse health effects from the exposure.

In contrast, while mutagens are agents that cause changes or mutations in genetic material, they do not specifically refer to the effects on fetal development or the occurrence of birth defects. Sterilants are substances that kill or render microorganisms inactive, which is unrelated to the effects on reproduction or fetal development. Carcinogens are agents that can cause cancer, but they do not specifically entail the risks of causing birth defects. Thus, the specific characteristics of teratogens align precisely with the question about causing birth defects while leaving the parent unharmed.