Thyroid hormones interact with other hormones, mainly reproductive hormones. Therefore, their correct functioning is essential for ovulation, embryo implantation, and maintaining a healthy pregnancy.

Thyroid dysfunction is more common in women than in men, antithyroid antibodies are detected in 5% of women, and these autoantibodies may predispose women to pregnancy loss.

Thyroid disorders have been shown to be a cause of infertility in a significant percentage of patients. In addition, subclinical hypothyroidism and undiagnosed and untreated hypothyroidism are common in women of reproductive age, occurring in 95% of these cases.

Thyroid Dysfunction And Its Relationship With Infertility

Sometimes they are asymptomatic, manifest with irregular menstruation, and are associated with fertility problems. However, they also occur in women with clear symptoms, generally associated with anovulation (absence of ovulation) and amenorrhoea.

It is imperative to diagnose subclinical and asymptomatic hypothyroidism to achieve and maintain pregnancy. In pregnant women, thyroid dysfunction is associated with increased foetal morbidity/mortality in utero and the newborn.

Hyperthyroidism And Hypothyroidism

Given the above, screening women with infertility for T4, TSH and TPO antibodies (antithyroid antibodies) concentrations is essential.

Hyperthyroidism in pregnancy is usually caused by Graves’ disease, an autoimmune disorder. The immune system produces antibodies that cause the thyroid to make too much thyroid hormone. This condition increases maternal and foetal morbidity and mortality, increasing the risk of miscarriage, pre-eclampsia, and even intrauterine growth retardation.

Cases of hypothyroidism may be due to an autoimmune mechanism such as Hashimoto’s disease or iatrogenic, among others. The incidence of frank hypothyroidism, associated with infertility and obstetric complications (repeated miscarriages, gestational hypertension and postpartum haemorrhage) is 0.5%, and subclinical hypothyroidism, which interferes with the release of an egg from the ovary (anovulation), is 4%.

Therefore, it is clear that its prevalence in women is high at 5/1000. Furthermore, it is directly related to infertility, and its manifestation affects both becoming pregnant and the evolution of the pregnancy.

Diagnosis And Treatment

The good news is that the problems derived from thyroid dysfunction are easy to diagnose and treat, so they should be carried out in all infertile women who need a fertility study by testing TSH and T4 determinations. This analysis provides us with the key to treating them, as the simple administration of thyroid hormone solves the problem. TSH levels must be kept within a range of less than 2.5 mU/L before and during the first trimester of pregnancy, and in the second trimester, below 3 mUL/. Iodine supplementation (more than 250 micrograms/day) is also recommended before and during pregnancy to maintain the metabolism of the thyroid gland.

Cases of hyperthyroidism are easier to detect. It would be treated with antithyroid medication to stabilise the metabolism. It is, therefore, necessary to test any woman who wishes to become pregnant with a TSH, T4 and TPO antibodies analysis to diagnose and solve the problem and avoid the consequences that it may entail.

Dr José López Gálvez, director of Vistahermosa Clinic, Reproduction Unit

Get expert advice on fertility and IVF

Get expert advice on IVF options

Learn all about IVF
Prices, success rates, quality standards and more

Get information on Redia’s IVF guarantee plans
The best refund guarantee for infertility

Ask our experts
Get answers to all your IVF-related questions