Why do some women experience thyroid problems after giving birth?
After delivery, the immune system sometimes overshoots and damages the thyroid, leading to temporary hormonal disturbances in approximately 5% of women. If you have thyroid antibodies or have previously experienced postpartum thyroiditis, discuss monitoring of your thyroid function with your doctor.
During pregnancy, the body suppresses the immune system to prevent it from attacking the baby. After delivery, that brake is released and the immune system can rebound. In some women, this rebound is directed at the thyroid: white blood cells damage thyroid tissue, causing thyroid cells to leak hormone. This phenomenon is called postpartum thyroiditis and affects approximately 5% of all women in the first year after delivery.
The condition often unfolds in phases. First, the leaking hormone causes a temporarily overactive thyroid: you may feel agitated, warm or restless. Once the hormone supply is depleted, a period of an underactive thyroid follows: fatigue, feeling cold and low mood are commonly reported complaints. In most women the thyroid recovers on its own after this, but some are left with a permanently underactive thyroid.
Women who already have antibodies against the thyroid enzyme TPO (the enzyme that helps produce thyroid hormone) before or during pregnancy are at greater risk of postpartum thyroiditis. Those antibodies are also the hallmark of Hashimoto's thyroiditis, the most common autoimmune disease of the thyroid, which is in any case more prevalent in women. If you already have those antibodies in your blood, the likelihood of symptoms after delivery is therefore considerably higher.
If you have had postpartum thyroiditis before, the risk of it recurring in a subsequent pregnancy is increased. The risk of permanent hypothyroidism in the long term is also greater. Regular monitoring of thyroid function is then advisable. A less well-known pitfall is a high iodine intake, for example through certain X-ray contrast agents or supplements: women with a history of postpartum thyroiditis appear to be more sensitive to this.
Finally, in a small group of women with severe psychiatric symptoms after delivery, an autoimmune thyroid inflammation is sometimes the underlying or contributing cause. This applies to a minority, but it underlines why thyroid testing can be worthwhile when notable psychological symptoms arise after delivery.
All claims are based on PMID 30844908, 34983968, 34913664, 24434360, 38044176, 11396709, 28290237 and 27609245. These consist largely of observational studies and clinical guidelines; there is no large RCT evidence for the causality of the immune mechanisms, but the associations are consistent and the pathophysiology is well described.