Final answer:
The categories of risk of harm to the fetus or nursing mothers include exposure to teratogens, such as alcohol, drugs, smoking, and infections. The duration, timing, and degree of transfer from maternal to fetal circulation are also important factors. Pregnant women should avoid toxins and prioritize proper nutrition.
Step-by-step explanation:
There are several categories of risk of harm to the fetus or nursing mothers. One category includes exposure to teratogens, which are environmental agents that cause damage to the developing embryo or fetus. Examples of teratogens include alcohol, drugs, smoking, and infections like rubella. Another category of risk is the duration and timing of exposure to teratogens, as well as the degree of transfer from maternal to fetal circulation. It is important for pregnant women to avoid toxins and ensure proper nutrition for normal fetal growth and development.