During postpartum thyroiditis, you might experience two phases. The inflammation and release of thyroid hormone might first cause mild signs and symptoms similar to those of an overactive thyroid (hyperthyroidism), including:

• Anxiety
• Irritability
• Rapid heartbeat or palpitations
• Unexplained weight loss
• Increased sensitivity to heat
• Fatigue
• Tremor
• Insomnia

These signs and symptoms typically occur one to four months after delivery and last one to three months.

Later, as thyroid cells become impaired, mild signs and symptoms of underactive thyroid (hypothyroidism) might develop, including:

• Lack of energy
• Increased sensitivity to cold
• Constipation
• Dry skin
• Weight gain
• Depression

These signs and symptoms typically begin four to six weeks after the symptoms of hyperthyroidism resolve and can last six to 12 months.

Keep in mind, however, that some women who have postpartum thyroiditis develop symptoms of only hyperthyroidism or only hypothyroidism.

The exact cause of postpartum thyroiditis isn't clear. However, women who develop postpartum thyroiditis often have high concentrations of anti-thyroid antibodies in early pregnancy and after childbirth. As a result, it's believed that women who develop postpartum thyroiditis likely have an underlying autoimmune thyroid condition that flares after childbirth due to fluctuations in immune function. This underlying condition appears to be very similar to Hashimoto's thyroiditis, in which the immune system attacks the thyroid gland.

You might be at increased risk of postpartum thyroiditis if you have:

• An autoimmune disorder, such as type 1 diabetes
• A history of postpartum thyroiditis
• High concentrations of anti-thyroid antibodies
• A history of previous thyroid problems
• A family history of thyroid problems

While further research is needed, some studies have also shown a link between postpartum thyroiditis and postpartum depression. As a result, if you have postpartum depression your doctor will likely check to see how your thyroid is functioning.

For most women who develop postpartum thyroiditis, thyroid function eventually returns to normal — typically within 12 to 18 months of the start of symptoms. However, some women who experience postpartum thyroiditis don't recover from the hypothyroid phase. As a result, they develop hypothyroidism, a condition in which the thyroid gland doesn't produce enough of certain important hormones.