is associated with intrauterine growth restriction, fetal goiter, fetal hydrops, preterm delivery and fetal death. Thus, any suspicion of this diagnosis warrants urgent ultrasound scanning of the fetus and treatment in a specialist fetal medicine center.
The size of the maternal goiter should be monitored clinically during pregnancy. Investigations such as ultrasound scanning of the thyroid gland and a flow‐volume loop should be considered if there is significant enlargement of the gland or development of symptoms suggestive of tracheal or esophageal compression.
There is greater than 50% chance that Graves’ disease will flare postpartum and thyroid function tests should be performed over the course of the following 6 to 9 months. Breast feeding is considered safe with the lower doses of carbimazole and PTU (up to 30 mg or 300 mg daily, respectively) administered postfeeds. Monthly thyroid function tests in the baby should be considered on higher dose regimens.
Key points
Challenge: ART in women with thyroid disease.
Background:
Abnormal thyroid function, particularly during the first trimester of pregnancy, is associated with increased pregnancy risks and can impact on the neurodevelopment of the child.
Controlled ovarian stimulation and pregnancy are associated with increased thyroxine requirements.
Carbimazole, methimazole and propylthiouracil are associated with teratogenicity, but the risk is least with propylthiouracil.
Reference ranges for thyroid function tests vary according to the laboratory assay, ethnicity of the population and stage of pregnancy. Thyroid treatments should ideally be optimized.
Management options:
In hypothyroid women already on thyroxine treatment:Thyroxine dosage should be increased at the start of ovarian stimulation and as soon as pregnancy is confirmed to prevent the development of hypothyroidism.Thyroid function test should be performed every 4–6 weeks during pregnancy.Thyroxine requirements should be adjusted to maintain TSH within the lower half of the trimester specific reference ranges.
In hyperthyroid women on anti‐thyroidal treatment:If on carbimazole or methimazole, convert to propylthiouracil prior to conception.Thyroid function test should be performed during COS and every 2–4 weeks during pregnancy.Antithyroid treatment should be kept to the minimum dosage required to maintain free T4 concentrations in the upper third of the normal range.
Answers to questions patients ask
1 Q1 Is levothyroxine safe to be taken in pregnancy? A1. Yes. Levothyroxine is identical to the natural thyroid hormone you produce and replaces the deficiency you have. Inadequate replacement will increase your risk of pregnancy loss and complications. Thyroxine requirements go up during ovarian stimulation and in pregnancy, so we recommend increasing your dose of levothyroxine at the start to prevent your thyroid function becoming abnormal.
2 Q2 Will taking too much levothyroxine harm my baby? A2. little too much levothyroxine taken over a short period of time does not harm your pregnancy, but too little levothyroxine is more likely to lead to complications. So, we would aim to keep your thyroid function at the more favorable end of the normal range. This means that we have to monitor your thyroid function regularly during pregnancy and adjust the dose accordingly.
3 Q3 If the drugs I take to control my overactive thyroid could cause abnormalities in the baby should I not stop them at the start of pregnancy? A3. The absolute additional risk of abnormalities with these drugs is still relatively small around 2–3%. However, the risk of pregnancy loss and other serious complications with uncontrolled hyperthyroidism is 50% or more. Hence the risk‐benefit ratio is very much in favor of continued treatment at the start of pregnancy if your hyperthyroidism has not been under control. We will monitor your thyroid function regularly to ensure you are kept well‐controlled on as low a dose of the drug as possible. In many cases the drug can be gradually tailed off and stopped later in pregnancy.
4 Q4 Why do I need my thyroid function checked so often during pregnancy? A4. There are a lot of hormonal changes occurring as your pregnancy progresses. The largest changes occur in the first half of pregnancy. These changes influence your thyroid condition and also alter the requirements for your thyroid treatment. Regular testing ensures that your thyroid function is optimal so that pregnancy complications and harms to your baby can be minimized.
References
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