Final answer:
Transient newborn hypothyroidism is most directly caused by 1) maternal iodine deficiency, which disrupts fetal thyroid hormone production necessary for brain development and growth. Other listed options, such as congenital hypothyroidism, thyroid hormone resistance, and thyroid hormone excess, aren't directly related to transient forms associated with maternal nutritional status.
Step-by-step explanation:
The cause of transient hypothyroidism in newborns most directly associated with the options provided is maternal iodine deficiency. This form of hypothyroidism, if related to iodine deficiency, presents because the developing fetus requires adequate iodine for the production of thyroid hormones crucial for brain maturation and growth development. Disturbances in cognitive abilities and even physical growth can result if the fetus does not receive enough thyroid hormones while in utero, due to the mother's iodine deficiency.
Newborn hypothyroidism can also result from congenital issues (present at birth) that are unrelated to maternal iodine intake, such as developmental abnormalities of the thyroid or genetic disorders affecting hormone production. However, among the options listed, maternal iodine deficiency is a main contributing factor for transient hypothyroidism in newborns. It's important to note that Hashimoto's thyroiditis is a different condition that usually affects adults and is characterized by the immune system attacking the thyroid gland, leading to hypothyroidism. The answer is option 1.