8 Significant Facts about Subclinical Hypothyroidism in Pregnancy|2023

What is subclinical hypothyroidism?

Subclinical hypothyroidism is described by a normal free thyroxine (T4) in the presence of an increased TSH (Thyroid-stimulating hormone).

Thyroxine or T4 is a type of thyroid hormone secreted by the thyroid gland into the bloodstream. Thyroxine plays a significant role in basal metabolism, digestive and heart function, bone health, brain development, and muscle control. While, thyroid stimulating hormone (TSH) is secreted from the pituitary gland (a pea size gland situated in the base of the brain), responsible to tell your thyroid how much thyroid hormone it requires to make. If the thyroid hormone values in the blood are too low, the pituitary gland creates a larger amount of TSH to inform the thyroid to work more.

Read more What is Subclinical Hypothyroidism and Hypothyroidism

Pregnancy in subclinical hypothyroidism 

may be associated with adverse outcomes: 

1. Does subclinical hypothyroidism affect pregnancy?

There is conflicting and inconsistent data available associated with subclinical hypothyroidism to adverse pregnancy results.   

Various Studies showed an association between subclinical hypothyroidism in pregnancy and preterm labor, hypertensive disorders, and impaired cognitive progression in infants. Though, more current studies have not repeated these associations.

2. What are the considerably higher limits of TSH in pregnancy with subclinical hypothyroidism?

In pregnancy, subclinical hypothyroidism occurrence is more frequent than overt hypothyroidism, ranging from 15% to 38% in iodine-sufficient areas. The higher limit of normal for TSH varies by trimester and it should be identified by the laboratory to reflect the local residents. If these data are not available, a higher limit of 0.4 mlU/L might be used.   

Read more Hyperthyroidism or Overactive thyroid

3. Is common screening for subclinical hypothyroidism should be done during pregnancy?

A common screening has not been shown to decline adverse outcomes when compared with targeted screening. This is highly recommended to women get their tests as soon as pregnancy is confirmed. 

4. What are the risk factors of subclinical hypothyroidism?

The following risk factors are associated with subclinical hypothyroidism

1.      Positive thyroid antibodies

1.      Geographic area with iodine deficiency

1.      Personal or family history of thyroid disease

1.       Type 1 diabetes and other autoimmune diseases

1.      Two or more previous pregnancies

1.      Head or neck radiation exposure

1.      Previous or current amiodarone or lithium use 

1.      History of preterm delivery, infertility, miscarriage

1.      Age older than 30

1.      Morbid obesity body mass index >4

 

5. Do pregnant women with subclinical 

Hypothyroidism and Thyroid peroxidase 

Antibodies need thyroid replacement therapy? 

50 % of the women with subclinical hypothyroidism have circulating thyroid peroxidase antibodies (TPOAb), which confirms the risks of adverse outcomes. The TPOAb-positive pregnant women with TSH of more than 2.5 mlU/L should be estimated.

The women who were positive for TPOAb should be treated with levothyroxine targeted to the lower half of the trimester-specific TSH range. The women who TPOAb- negative should be treated only if their TSH is higher than 10.0mlU/L. Levothyroxine should be taken separately from iron supplements or prenatal because interaction can affect absorption.  

6. Do the patients with hypothyroidism in pregnancy 

need postpartum treatment? 

Levothyroxine can typically be stopped postpartum, except for patients who were on thyroid replacement therapy pre-conception. 

Postpartum thyroiditis may occurs in about 5% of women, with a higher rate in those with TPOAb during pregnancy. The TSH and free thyroxine levels of women with subclinical hypothyroidism should be measured 6 weeks postpartum.  

If symptoms of hypo or hyperthyroidism are well-known, referral to a specialist should be considered.   

A new study shows women treated for subclinical hypothyroidism during pregnancy are less probable to experience pregnancy loss, but they face a higher risk of complications for example gestational diabetes, preterm delivery, and pre-eclampsia. 

Read more What is Thyroid Storm?

7. At what TSH level should hypothyroidism be 

treated in pregnancy?

Health experts suggest treatment with levothyroxine for women having a TSH level of more than 10 mlU/L in the first trimester of pregnancy. On the other hand, women don’t require treatment if the TSH values are 2.5 or less.   

8. Is hypothyroidism in pregnancy high risk?

Women with hypothyroidism decline in fertility, even if they get pregnant, the risk of abortions is elevated, and the risk of gestational hypertension, postpartum hemorrhage, and abruption in the placenta, is augmented.

The risk factors mentioned above are more in women with overt hypothyroidism, rather than subclinical hypothyroidism.