Thyroid Disease and Female Reproduction

Thyroid Disease and Female Reproduction
The menstrual pattern is influenced by thyroid hormones directly through impact on the ovaries and indirectly through impact on SHBG, PRL and GnRH secretion and coagulation factors. Treating thyroid dysfunction can reverse menstrual abnormalities and thus improve fertility. In infertile women, the prevalence of autoimmune thyroid disease (AITD) is significantly higher compared to parous age-matched women. This is especially the case in women with endometriosis and polycystic ovarian syndrome (PCOS). AITD does not interfere with normal foetal implantation and comparable pregnancy rates have been observed after assisted reproductive technology (ART) in women with and without AITD. During the first trimester, however, pregnant women with AITD carry a significantly increased risk for miscarriage compared to women without AITD, even when euthyroidism was present before pregnancy. It has also been demonstrated that controlled ovarian hyperstimulation (COH) in preparation for ART has a significant impact on thyroid function, particularly in women with AITD. It is therefore advisable to measure thyroid function and detect AITD in infertile women before ART, and to follow-up these parameters after COH and during pregnancy when AITD was initially present. Women with thyroid dysfunction at early gestation stages should be treated with L-thyroxine to avoid pregnancy complications. Whether thyroid hormones should be given prior to or during pregnancy in euthyroid women with AITD remains controversial. To date, there is a lack of well-designed randomized clinical trials to elucidate this controversy.

Procreation is a fundamental evolutionary process necessary to sustain life and involves spatio-temporally regulated endocrine, cellular and molecular events. Before ovarian follicles are expelled, oocyte maturation demands a favourable endocrine environment, including normal levels of thyroid hormones. The major factors that establish uterine receptivity for implantation and further embryo development are progesterone, oestrogens and the immunological system. Infertility and reproductive impairment can be compromised by abnormalities in both the endocrine and the immune system. A close interplay between thyroid hormones and normal steroid action and secretion exists, necessary for normal ovarian function and thus fertility. Women with thyroid dysfunction often have menstrual irregularities, infertility and increased morbidity during pregnancy. The impact of thyroid dysfunction on the outcome of spontaneous pregnancy has been the subject of several recent review articles. Therefore, in the present review, our aim was to focus on the period preceding pregnancy and in particular on the interaction between thyroid disorders and all aspects of infertility. These aspects include the occurrence of thyroid disorders (dysfunction and autoimmunity) in female infertility, the impact of high oestrogen levels in preparation for assisted reproduction technology (ART) on thyroid hormones, and the consequences of thyroid disorders on the outcome of assisted pregnancies.