Thyroid disease can have significant effects on a woman’s reproductive health and screening for women presenting with fertility problems and recurrent early pregnancy loss should be considered, suggests a new review published today (23 January) in The Obstetrician & Gynaecologist (TOG).
The review examines the effect of thyroid disorders on reproductive health and reviews the current evidence on how to optimise thyroid function to improve reproductive outcomes.
Thyroid hormones control the metabolism via the production of two hormones triiodothyronine and thyroxine. These hormones also have key roles in growth and development, particularly brain development. Changes in thyroid function can impact greatly on reproductive function before, during and after conception.
Thyroid disease is divided into hyperthyroidism (overactive thyroid) and hypothyroidism (underactive thyroid), and the causes of the diseases are numerous.
The review highlights that hyperthyroidism is found in approximately 2.3% of women presenting with fertility problems, compared with 1.5% of women in the general population. The condition is linked with menstrual irregularity. Hypothyroidism affects around 0.5% of women of reproductive age. Hypothyroidism in childhood and adolescence is associated with a delay in reaching sexual maturity, and in adulthood is associated with menstrual problems and in some cases a lack of ovulation, state the authors.
The authors note that thyroid disease has long been associated with fertility problems, however, national guidance does not currently recommend routine measurement of thyroid function in asymptomatic women presenting with problems conceiving.
Additionally, the authors of the review note that miscarriage is common, affecting approximately one in five pregnancies and recurrent miscarriage, defined as three consecutive miscarriages, affects 1% of couples. Given that thyroid hormone plays an important part in embryonic development, thyroid disease has long been associated with an increased risk of miscarriage.
Thyroid disease, in particular hyperthyroidism, can also have a significant effect on pregnancy, the authors of the review state. Adverse outcomes can include preterm delivery, pre-eclampsia, growth restriction, heart failure and stillbirth.
How a thyroid disorder affects a woman’s body
The functions of the thyroid gland have much to do with a woman’s reproductive system, particularly if the thyroid is overactive or underactive. Effects of this imbalance in hormone levels may have the following effects on a woman’s body:
Puberty and menstruation
Thyroid disorders can cause abnormally early or late onset of puberty and menstruation. In addition, abnormally high or low levels of thyroid hormone can cause very light or very heavy menstrual periods, very irregular menstrual periods, or absent menstrual periods (a condition called amenorrhea).
An overactive or underactive thyroid may also affect ovulation (the release of an egg for fertilization). Thyroid disorders may prevent ovulation from occurring at all. In addition, the ovaries are at an increased risk for cyst development if the woman has an underactive thyroid (hypothyroid). Severe hypothyroidism can actually cause milk production in the breast, while preventing ovulation.
Pregnancy and postpartum
Thyroid disorders during pregnancy can harm the fetus and may lead to thyroid problems in the mother after birth, such as postpartum thyroiditis.
Thyroid disorders may cause the early onset of menopause (before age 40 or in the early 40s). In addition, some symptoms of hyperthyroidism (overactive thyroid), such as lack of menstruation, hot flashes, insomnia, and mood swings may be mistaken for early menopause. Treating hyperthyroidism sometimes can alleviate symptoms of, or the actual onset of, early menopause.
The authors conclude that screening for thyroid disease should be considered in women presenting with fertility problems and recurrent pregnancy loss. Additionally, the authors highlight that there is evidence to suggest that routine screening of the general population for thyroid dysfunction at the start of pregnancy may be beneficial.
Furthermore, women diagnosed with thyroid disease should continue on anti-thyroid medication throughout pregnancy and receive close monitoring, emphasise the authors.
Amanda Jefferys, from the Bristol Centre for Reproductive Medicine, Southmead Hospital, Bristol, and co-author of the study said:
“Abnormalities in thyroid function can have an adverse effect on reproductive health and result in reduced rates of conception, increased miscarriage risk and adverse pregnancy and neonatal outcomes.
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.
“However, with appropriate screening and prompt management, these risks can be significantly reduced.”
Jason Waugh, TOG Editor-in-chief, added:
“Thyroid disease is common in the reproductive medicine setting, in fact, it is the most common endocrine condition affecting women of reproductive age.
“This paper highlights how thyroid disorders can affect fertility and pregnancy and makes a case for universal screening.”
Obstetrician & Gynaecologist