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Thyroid Function and Fertility

Thyroid Health and Overall Fertility

As part of the endocrine system, a large network of chemical messengers and receptors in the body, the thyroid plays a significant role in female reproductive health and the menstrual cycle. Thyroid function involves thyroid stimulating hormone (TSH) which acts as a communicator from the brain to the thyroid gland, and thyroxine (T4) and triiodothyronine (T3) which are released from the thyroid tissue. Thyroid hormones promote normal growth and development, metabolism, heart rate, nervous system activity, endometrium (uterine) thickening, and breakdown of protein and carbohydrates – that’s a lot of activity!

Pregnenolone is a cholesterol-heavy hormone and precursor to all sex hormones including estrogen, progesterone, testosterone, DHEA, and cortisol. Research has shown that people with reduced thyroid function also have low pregnenolone levels which in turn impacts hormone levels and balance.

People with thyroid dysfunction such as hypo- and hyperthyroidism are more likely to experience irregular ovulation and therefore irregular periods. Hypothyroidism (low thyroid function) is also associated with spontaneous miscarriage and recurrent pregnancy loss. This is why supporting healthy thyroid function prior to pregnancy is recommended.

Stress can also have a negative impact on thyroid function through the action of cortisol. There is a delicate balance needed however, as cortisol is required to convert inactive T4 to active T3, but high or chronic levels suppress TSH, inhibit thyroid hormone conversion and block thyroid hormone receptors.

Thyroid Health and Pregnancy

Healthy thyroid function supports successful conception and pregnancy. As we know good thyroid function is important for sex hormone production and regular ovulation and menstrual cycles. This regularity is crucial for adequate progesterone production via the corpus luteum, the tissue from which the egg was release. During pregnancy, progesterone acts as an immunomodulator that reduces inflammation and promotes the supportive Th-2 cytokine response. This is highly important for overall wellbeing including bone health as well as maintaining a healthy pregnancy. During mid-pregnancy the placenta takes over this role.

Maternal thyroxine (T4) is required for neural development and normal central nervous system function. Thyroid hormone (T4) is delivered to the baby during gestation and comes directly from the mother’s stores during the first half of pregnancy. After this time the baby’s own production of thyroid hormone begins. The placenta also regulates the amount of thyroid hormones transferred to the baby during pregnancy.

The preconception care period (the months of active preparation and nutritional support prior to pregnancy) is the ideal time to assess and address any thyroid dysfunction. Thyroid dysfunction is also associated with reduced fertility, increased risk of

miscarriage, increased risk of pre-term delivery, hypertension, and pre-mature birth. Dietary support including assessing the levels of thyroid-supporting nutrient intake can be highly effective at addressing thyroid concerns.

What about Testing?

Adequate thyroid function assessment includes testing of TSH, T4, T3, as well as rT3 and thyroid anti-bodies in the case of screening for or monitoring auto-immune related thyroid conditions.

T4 and T3 are largely made up of iodine. insufficient iodine levels in the body is associated with poor thyroid function, goitre (enlargement of the thyroid gland) and poor thyroid growth during pregnancy.

Assessing intake and dietary status of selenium, iodine, and other nutrients required for hormone conversion and activity such as zinc, tyrosine, vitamin D, vitamin A, vitamin B6, magnesium, and vitamin C. Supplements should not be taken for thyroid health without professional assessment and support as under active function can swing into an overactivity with incorrect dosing.


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