Pregnancy can reveal a thyroid problem that was previously hidden  

Pregnancy places substantially greater demands on the maternal thyroid. The resulting fatigue, constipation, low motivation, poor concentration and sleepiness are easily dismissed as normal features of pregnancy.

After delivery, immune-system rebound can trigger postpartum thyroiditis or aggravate previously quiet Hashimoto’s thyroiditis, producing symptoms that overlap almost perfectly with postpartum depression (PPD).

We need to get stricter when looking at the thyroid in pregnancy 

Hypothyroidism is commonly missed in the general population. Using TSH as the only screen is inadequate [1]. You need to consider the symptoms and not just rely on tests.

Symptoms matter (maybe as much as labs): Hypothyroid symptoms can include low body temperature and feeling cold when others do not, fatigue, lack of motivation, poor memory, loss of interest in sex, dry or scaly skin, high cholesterol, muscle cramps at rest, constipation, cysts and fibroids, unexplained sadness or crying, menstrual-related mood swings, difficulty losing weight, puffiness under the eyes, ankle swelling, depression and frequent colds.

Support the thyroid, even if it is “borderline”  

Even borderline high TSH levels are linked to a higher risk of miscarriage, gestational hypertension, and lower infant neurocognitive scores [2]. While it may be extreme to take a drug for these “borderline” levels, you can still improve thyroid function.

  • A TSH of 2.5 is not necessarily a reason to prescribe a drug. It is a reason to pay attention. The British Thyroid Foundation recommends paying attention to TSH over 2.5 in pregnancy and in women wanting to get pregnant [3]. In the presence of hypothyroid symptoms, a TSH above 2.5 should signal you to take action [2]. Note: some practitioners will act if the TSH is 2.0 and symptoms are present.
  • Safely, naturally support the thyroid: Researchers found that 94.1% of pregnant women treated with a combination of Myo-Inositol and selenium successfully maintained normal thyroid hormone levels (euthyroidism) throughout their pregnancy, compared to only 68.7% in the untreated control group [4,5]. Myo inositol is safe, even at very high (2g/day) doses. Too much selenium can be toxic and you should take less than 100 mcg/day (200 mcg/day can be safe, but there may be selenium in the prenatal vitamin).

Iodine, Maternal Thyroid, and PPD  

When you think of the thyroid, you think of iodine. Hypothyroidism and PPD are linked, so what about iodine supplementation? Recently, a lot of focus has been placed on high doses of iodine as a therapy for hypothyroidism, fibroids, PCOS and a variety of other health issues. The argument for the therapy is that we consume toxic halides, like fluoride, chlorine, bromine, which displace iodine and create extreme deficiencies. Taking a high dose of iodine can be dangerous:

  • Wolff–Chaikoff effect: A sudden large iodine dose can temporarily suppress thyroid-hormone production. Most people adapt, but susceptible individuals may remain hypothyroid.
  • Jod–Basedow effect: Excess iodine can trigger hyperthyroidism, particularly in people with autonomous thyroid nodules, multinodular goiter or previously unrecognized thyroid disease.

Stopping the iodine will usually stop the Wolff-Chaikoff effect, but the Jod-Basedow effect is usually permanent. The RDA for iodine is 150 mcg/day. The WHO recommends 250 mcg/day (150 mcg supplement plus 100 mcg from the diet). Anything over 1.1 mg/day is possibly dangerous and is discouraged. Some practitioners use high doses (12 mg/day or more), but the thyroid must be thoroughly examined and nodules ruled out. Do not randomly take a lot of iodine because of something you read.

Iodine and PPD: Studies have linked low iodine consumption to PPD. For women not using supplements, a low habitual iodine intake from food (under 100–150 mcg/day) was significantly associated with a higher risk of elevated emotional distress and depression scores both during pregnancy and at six months postpartum [6,7].  Some practitioners may recommend a slight increase in iodine supplementation, like 250 mcg/day.

T4-T3 Conversion and Reverse T3 (rT3)

Dr. Harry Eidenier wrote extensively about “normal” lab values and how they may show physiological need. “Normal” is not necessarily healthy according to Dr. Eidenier. He had some interesting things to say about T3 and T4 levels.

T3 is more active than T4. According to Dr. Eidenier, if the T3 is below the middle of the reference range and the T4 is above the middle of the reference range, it is a conversion problem. T4 is converted by the body to the more active form, T3. In the presence of symptoms, this needs to be addressed. To aid conversion:

  • Selenium is necessary for T4-T3 conversion.
  • Insulin resistance can interfere with conversion. The effect is bidirectional. Poor thyroid function increases insulin resistance as well [10,11].
  • Stress can interfere with conversion [8].
  • Good liver function is necessary for conversion [12]. Phosphatidylcholine is a safe way to support liver function (see below).
  • Magnesium is one supplement that helps address both stress and insulin resistance. B vitamins may also be useful here.

rT3: Reverse T3: During illness, inflammation, severe stress or calorie restriction, the body may reduce the activation of T4 to T3 while increasing the production or slowing the clearance of reverse T3. Reverse T3 is metabolically inactive and may provide additional evidence that thyroid-hormone metabolism has shifted away from active T3. Some clinicians find the test useful when symptoms and conventional laboratory results do not agree [9].

Pregnancy and lactation create an enormous demand for choline. Choline and phosphatidylcholine are actively transferred to the placenta, fetus and breast milk, while estrogen increases the liver’s PEMT pathway to help meet the demand. Nevertheless, maternal stores can become depleted when dietary intake is inadequate. Because phosphatidylcholine is needed to maintain liver-cell membranes and package triglycerides into VLDL for export, deficiency can promote fat accumulation and impair liver function. Since the liver is also a major site of T4-to-T3 conversion, inadequate choline represents another possible link among pregnancy, fatty liver, insulin resistance and thyroid hypofunction [13-15].

Related Articles:

Postpartum Depression? Check the Thyroid

Bottom Line 

Pregnancy can expose limited thyroid reserve, and postpartum immune changes can aggravate Hashimoto’s disease or trigger postpartum thyroiditis. The resulting fatigue, poor concentration, loss of motivation, weight retention, sleep disturbance and depression can be almost indistinguishable from PPD. That does not mean every case of PPD is a thyroid problem. It means that thyroid function deserves a serious investigation rather than a quick glance at whether TSH falls inside the laboratory range.

Even with an arguably too high TSH cutoff, the Colorado Thyroid Disease Prevalence Study found previously unrecognized biochemical thyroid dysfunction in approximately one out of ten untreated participants. Imagine what we might uncover if borderline findings were evaluated alongside symptoms, free thyroid hormones, antibodies, nutritional status and metabolic health.

Thyroid dysfunction may be only one straw contributing to PPD. Insulin resistance, inflammation, altered stress physiology and an unhealthy microbiome may add others. The goal is not to force every woman into a single diagnosis; it is to identify and remove as many contributing straws as possible.

Selected References:

  1. British Medical Journal [BMJ 2000;320:1332-1334 (13 May)] Thyroid function tests—time for a reassessment
  2. Thyroid Res. 2018 May 21;11:5. The upper limit for TSH during pregnancy: why we should stop using fixed limits of 2.5 or 3.0 mU/l
  3. https://www.btf-thyroid.org/subclinical-hypothyroidism-in-conception-and-pregnancy
  4. Myo-inositol and selenium prevent subclinical hypothyroidism during pregnancy: an observational study IJMDAT 2018; 1 (2) : e164
  5. Front Endocrinol (Lausanne). 2022 Nov 16;13:1067029. Supplementation with myo-inositol and Selenium improves the clinical conditions and biochemical features of women with or at risk for subclinical hypothyroidism
  6. J Affect Disord. 2022 Dec 1:318:347-356. Mild-to-moderate iodine deficiency and symptoms of emotional distress and depression in pregnancy and six months postpartum – Results from a large pregnancy cohort
  7. Nutrients 2024, 16(11), 1771 Prenatal Iodine Intake and Maternal Pregnancy and Postpartum Depressive and Anhedonia Symptoms: Findings from a Multiethnic US Cohort
  8. Endokrynol Pol. 2026;77(3):127-133. The influence of stress and cortisol on thyroid dysfunction
  9. J Clin Invest. 2006 Oct 2;116(10):2571–2579. Deiodinases: implications of the local control of thyroid hormone action
  10. Journal of Thyroid Research 19 September 2011 Why Can Insulin Resistance Be a Natural Consequence of Thyroid Dysfunction?
  11. Endocr Rev. 2019 Jan 14;40(3):789–824. Thyroid Dysfunction and Diabetes Mellitus: Two Closely Associated Disorders
  12. 2023 Mar 24;15(3):e36618 Association of Thyroid Function and Severity of Illness in Liver Cirrhosis as Measured by Child-Pugh Score
  13. 2024 Jan 15;16(2):260. A Narrative Review on Maternal Choline Intake and Liver Function of the Fetus and the Infant; Implications for Research, Policy, and Practice
  14. 2019 Aug 7;11(8):1823. Choline: Exploring the Growing Science on Its Benefits for Moms and Babies
  15. BMJ Open Gastroenterol. 2020 Mar 26;7(1):e000368. Effectiveness of phosphatidylcholine as adjunctive therapy in improving liver function tests in patients with non-alcoholic fatty liver disease and metabolic comorbidities: real-life observational study from Russia