Practice question

Teratogen vulnerability peaks during organogenesis spanning post-fertilization weeks 3 to 8, when gastrulation creates organ primordia and morphogenetic gradients like Sonic hedgehog, retinoic acid and Wnt pattern tissues. Exposure during this window disrupts folding, migration and differentiation causing major congenital malformations of heart, neural tube, limbs. Earlier exposure weeks 1-3 typically results in all-or-nothing loss due to pluripotent regulative capacity, later fetal period weeks 8-12 onward results in functional deficits or growth retardation. Therefore clinicians emphasize avoidance of alcohol, retinoids, certain drugs specifically during weeks 3-8 as critical period of structural patterning and embryonic susceptibility.