Thyroid disease and pregnancy

Overview

Patients without known thyroid disease prior to pregnancy

There is no national screening programme for thyroid disease in pregnancy. Consider screening for thyroid disease (TSH) in those in a high risk group who are planning a pregnancy. High risk groups include:

• Previous positive TPO antibodies
• Personal history of thyroid disease
• First degree relative with thyroid disease
• Autoimmune disease
• Presence of a goitre
• Recurrent miscarriage (3 or more)
• Previous unexplained preterm delivery (<37 weeks)
• Taking lithium or amiodarone
• Past history of thyroid surgery or previous head/neck irradiation

In the setting of pregnancy, maternal hypothyroidism is defined as a TSH concentration beyond the upper limit of the trimestral specific range.

The normal references ranges in women without pre-existing thyroid disease as are follows:

Please note - the finding of an abnormal TSH during pregnancy does not imply lifelong hypothyroidism.

Patients with known thyroid disease prior to pregnancy

Advice from Natasha Thorogood (Consultant Endocrinolgist at UHBW) : 

Only around 40% of all women taking levothyroxine will need their dose adjusted in the first trimester. In addition, many women who are taking levothyroxine were commenced on it in the context of IVF treatment.

TFTs should be done in early pregnancy before any dose adjustment is undertaken.

Dose adjustments should then be made according to the chart below. 

Who to refer

• Most women with primary hypothyroidism can be managed in the community.
• Women with a previous history of Graves’ disease or thyroid cancer or who have previously received radioactive iodine / undergone a thyroidectomy should be referred to the endocrine antenatal clinic.
• Women with hyperthyroidism should be managed in the hospital endocrine antenatal clinic (ANC). Refer urgently to the Joint Antenatal Endocrine Clinic if poorly controlled Graves’ disease or new biochemical hyperthyroidism in pregnancy 

Before referral

Pre-conception management

• Levothyroxine is recommended for the management of those planning a pregnancy with sustained overt hypothyroidism or subclinical hypothyroidism
• Patients with positive TPO antibodies and a TSH in the normal range but ≥2.5, may be treated in the context of assisted conception
• Ideally Levothyroxine should be taken first thing in the morning on an empty stomach. It should not be taken at the same time as other medications, particularly pregnancy multivitamins as this can affect absorption.

Management during pregnancy

• In women with hypothyroidism the goal during pregnancy is to maintain the TSH within the trimestral specific target ranges using treatment with Levothyroxine. There is no evidence that women with adequately treated hypothyroidism have any increased risk of obstetric complications.

• The ranges for the assay used in Bristol are below:  

• Levothyroxine should usually be increased by 25-30% as soon as the pregnancy is confirmed. If the initial blood test shows thyroid function is currently normal (TSH<2.5), Levothyroxine should be increased by 25-30% as per the table below 

• If TSH >2.5, this suggests the woman is not on enough Levothyroxine. If she is taking more than 100mcg, in addition to the dose increase above, we would suggest increasing by a further 25mcg.
• If TSH>5, we would suggest increasing by a further 25mcg as above but also referring urgently to ANC.
• If TSH >2.5 and taking <100mcg, please advise the patient to increase the dose as per Table 1 but also refer the patient to the endocrine antenatal clinic for further advice.
• If initial TSH<0.02 this may reflect too much Levothyroxine but can also be normal in early pregnancy. If free T4 normal, simply keep on usual dose and repeat in 4 weeks. If free T4 also high, please refer for advice from the endocrine antenatal clinic.
• In women diagnosed with hypothyroidism during pregnancy they should be commenced on 50-100mcg  Levothyroxine
• Maternal TSH should be measured 4 weeks after any dose change. Once stable TSH should be tested every 6-8 weeks during first half of pregnancy, and again around 28 weeks.

Guide to adjusting Levothyroxine dose later in pregnancy

• Following delivery women should reduce their Levothyroxine back to their usual pre-pregnancy dose and have a blood test to check TSH at 6 weeks post-partum.
• Breast feeding is completely safe. 

Referral

Please see the Maternity Services page for advice on how to refer.

Efforts are made to ensure the accuracy and agreement of these guidelines, including any content uploaded, referred to or linked to from the system. However, BNSSG ICB cannot guarantee this. This guidance does not override the individual responsibility of healthcare professionals to make decisions appropriate to the circumstances of the individual patient, in consultation with the patient and/or guardian or carer, in accordance with the mental capacity act, and informed by the summary of product characteristics of any drugs they are considering. Practitioners are required to perform their duties in accordance with the law and their regulators and nothing in this guidance should be interpreted in a way that would be inconsistent with compliance with those duties.

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