Why are vitamin A derivatives and very high intakes of preformed vitamin A discouraged in people planning pregnancy?

Because these compounds are teratogenic and, being fat-soluble, can accumulate in tissues and persist long enough to cause fetal toxicity if conception occurs during or soon after exposure.

Because preformed vitamin A increases the risk of causing folate deficiency, which indirectly leads to teratogenicity in the second trimester only.

Because vitamin A derivatives are water-soluble and are rapidly excreted, they pose no risk to the fetus but are discouraged simply for cost reasons.

Because vitamin A reduces milk supply postpartum and therefore must be limited only during lactation rather than preconception or pregnancy.