The impact of teratogens on fetal development largely depends on the stage of pregnancy during which the exposure occurs. The embryonic period (weeks 3-8) is particularly vulnerable, as this is when organogenesis occurs, and the foundational structures of the body are forming. Teratogens can disrupt this process, leading to structural anomalies. During the fetal period (week 9 to birth), the risk is more associated with functional deficits and growth impairments.
