Thyroid hormones and nausea during pregnancy

Nausea and vomiting during pregnancy (also known as morning sickness) are common — occurring in 8 in 10 pregnant people (1). Sickness usually improves and stops around weeks 16 to 20 (1).

For about 3 in 100 pregnant people, nausea and vomiting are very severe — this is known as hyperemesis gravidarum (HG). HG can cause problems with keeping food and drink down, some people require hospital treatment (1).

Symptoms of hyperemesis gravidarum (1):

  • Severe nausea and vomiting (lasting longer than 20 weeks)
  • Fatigue
  • Thirst
  • Dark yellow urine
  • Weight loss
  • Low blood pressure

The connection between hyperemesis gravidarum and thyroid health (2–5)

Thyroid hormone levels change during pregnancy in order to support embryo growth. But there are also differences in thyroid hormone levels between pregnant people with mild or no nausea, and those with extreme nausea.

Thyroid hormone reverse T3 (rT3) is higher than usual in people with HG. This might be to help prevent weight loss caused by nausea and vomiting.

In some cases free T3 and free T4 might be higher than usual in HG patients, while TSH is slightly decreased. These changes in thyroid hormones are caused by human chorionic gonadotropin (hCG) — a hormone produced in early pregnancy that activates the thyroid gland in early pregnancy and can cause vomiting.

How we write: our information is based on the results of peer reviewed studies using the National Library of Medicine platform. It is written by scientists and reviewed by external experts. If you believe we might have overseen crucial scientific information, please contact us at

Disclaimer: This information is not intended to mitigate, prevent, treat, cure or diagnose any disease or condition. If you want to change your treatment, lifestyle, your diet, include supplements in your diet or have concerns about your health, please consult your doctor before trying new approaches.


  1. Jennings LK, et al. Hyperemesis Gravidarum, 2020
  2. Asakura H, et al. Severity of hyperemesis gravidarum correlates with serum levels of reverse T3, 2000
  3. Juras N, et al. Increased serum reverse triiodothyronine in patients with hyperemesis gravidarum, 1983
  4. Swaminathan R, et al. Thyroid function in hyperemesis gravidarum, 1989
  5. Appierto U, et al. Nausea, vomiting and thyroid function before and after induced abortion in normal pregnancy, 1996

Photo: Unsplash; Design: VLM Health



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