What condition may cause a newborn to initially appear normal but later exhibit symptoms of hypothyroidism?

The correct answer relates to maternal hormone influence, which can significantly impact newborns, particularly in the case of thyroid hormones. During pregnancy, the mother’s thyroid hormones cross the placenta and help in the development of the fetus, especially during the first trimester. After birth, there can be a period where the newborn continues to experience the effects of maternal hormones.

In some instances, following delivery, the infant may initially appear healthy as they are still under the influence of maternal thyroid hormones. However, once these hormones diminish—usually within the first few days to weeks of life—the baby may start showing signs of hypothyroidism if there is an underlying issue, such as congenital hypothyroidism that was not detected immediately.

This mechanism is critical in understanding how maternal hormone levels can mask underlying metabolic conditions in newborns, thereby leading to an initial normal appearance followed by symptoms consistent with hypothyroidism as those hormonal effects wane. In contrast, inherited metabolic disorders, congenital viral infections, and maternal drug exposure typically present with more consistent or observable symptoms upon birth rather than a delay in manifestation.