Why can too much vitamin A during pregnancy cause birth defects?

Vitamin A, in the form of retinoic acid, plays a critical role in the regulation of embryonic development and growth. Because of this essential function, the presence of excessive amounts of vitamin A or its derivatives—such as the acne medication isotretinoin—during pregnancy can disrupt these delicate developmental processes, leading to birth defects.1

Unlike water-soluble vitamins, vitamin A is fat-soluble and is stored in the liver rather than being eliminated in the urine. This storage capacity means that high intakes can lead to a toxic condition known as hypervitaminosis A. While the body requires vitamin A for proper functioning, maintaining appropriate levels is vital, especially during pregnancy, to avoid the risks associated with toxicity.1