P72.1: Transitory neonatal hyperthyroidism

The thyroid gland is a small organ in the neck below the larynx. It is made up of two sides that lie to the right and left of the trachea. The two sides are connected to each other by a bridge of thyroid gland tissue. The thyroid gland needs iodine to produce important messenger substances for the body. These messenger substances influence the heartbeat, digestion, and body temperature, among other things.

When the thyroid gland is hyperactive, too many thyroid gland messengers are produced. A hyperactive thyroid gland in a baby can be due to a disorder of the mother’s thyroid gland. With this thyroid gland disorder, the mother’s body produces antibodies that attack thyroid gland tissue. These antibodies cause more thyroid gland messengers to be produced than required. The mother’s antibodies can get into the child before birth, via the placenta. As a result, the child’s thyroid gland also produces too many thyroid gland messengers. The mother may also be receiving thyroid gland medication. This thyroid gland medication can also get into the child via the placenta, and affect the thyroid gland function.

The hyperactive thyroid gland can also cause health problems or damage while in the womb. For example, it can negatively affect the child’s growth. The head may be smaller than that of other children of the same age. Damage in the womb might prevent certain mental abilities from being able to develop properly later.

After the birth, the mother’s antibodies remain in the child’s blood for a certain time. But over time they get broken down. After the birth the hyperactive thyroid gland can temporarily cause other health problems. The baby may have a weak suck or palpitations, for example. The child may also grow slowly or suffer vomiting and diarrhea. The thyroid gland may also be enlarged.