How thyroid affects your fertility, pregnancy and your baby’s health
Many couples don’t realise the crucial role that the thyroid plays in male and female fertility. Healthy thyroid function is essential for robust reproductive system ranging from maintaining sex drive, production and release of eggs and sperm, the ability to conceive and to maintain a healthy pregnancy. The thyroid, along with other glands, influences all other hormones and interact to affect fertility in a variety of ways. Suboptimal thyroid function may be the “missing link” for those who have been diagnosed as having “unexplained infertility”.
The menstrual cycle is a carefully orchestrated process and thyroid problems can interrupt this in any phase. This can result in an irregular menstrual cycle or even the absence of menstruation/ovulation (anovulatory cycles) altogether which makes pregnancy impossible. The active thyroid hormone, T3 is required for progesterone release during the luteal phase, the second half of the menstrual cycle. A Luteal phase defect will prevent the secure implantation of a fertilised egg. The short luteal phase with insufficient progesterone can cause early miscarriage which is often mistaken as a regular period. A low thyroid function will also result in lower basal body temperature. As the rapidly dividing cells in an embryo require a specific temperature range for that division to take place, low basal body temperature prevents the embryo from continuing to grow and thus increases the risk of early miscarriage. The thyroid interacts with many other hormones; for example, a healthy thyroid facilitates balanced oestrogen and vice versa.
The thyroid has a significant regulatory role in male fertility and sperm production. Poor thyroid health in men can result in reduced testosterone production, a lower libido, erectile dysfunction, poor testicular function, as well as reduced sperm count and motility. There are thyroid hormone receptors on the Sertoli cells, the nurturing cells for sperm in the testes. The thyroid hormone, T3 binds to these receptors so directly influences sperm production.
Both hyper and hypothyroidism produce increased level of oxidative stress which damages the sperm DNA integrity and morphology.
Human foetuses acquire the ability to synthesise thyroid hormones at roughly 12 weeks of gestation until then the fetus relies entirely on the mother to provide thyroid hormones for its growth and development. Thyroid hormone is essential for neurological and brain development of the foetus, most significantly during the first trimester.
Pregnancy: Stress test for the thyroid
During pregnancy, your thyroid gland needs to expand its function so as to meet the needs of both mother and developing baby. If you have a healthy thyroid, increased thyroid hormone production begins and continues until the baby is born. If you can’t meet the increased need for thyroid hormone and if you have a limited thyroidal reserve, this results in an increase in TSH levels, and hypothyroidism. This condition is associated with adverse outcomes, including miscarriage, preterm birth, stillbirth, gestational diabetes, breech delivery, a higher risk of a C-section, and cognitive function deficits in the child, including ADHD, autism, cognitive and learning disabilities, and even mental retardation.
Assisted reproduction: additional strain on the thyroid
Some ART can be impacted by thyroid function and thyroid autoimmunity. Various studies have shown that women with hypothyroidism, even when treated, aren’t as responsive to fertility drugs; the ovaries are less likely to respond with ovulation. High estrogen levels induced by fertility drugs can further block the thyroid receptors. Control of TSH levels is crucial in women undergoing assisted reproduction who are positive for TPO Antibody. Unsuccessful procedures and miscarriage rates are higher in women who have a TSH level above 2.8 who also test positive for TPO.