Which of the following influences the likelihood that a teratogen will cause a birth defect?

A) Timing of exposure
B) Dose
C) Duration
D) All of these

All of these factors play a role in the likelihood of a teratogen causing a birth defect. The timing of exposure, dose, and duration can all impact the degree of risk for a developing fetus. For example, exposure to certain teratogens during critical periods of embryonic development may be more harmful than exposure at other times. Likewise, higher doses or longer durations of exposure can increase the risk of birth defects as well.