Krassas, G. E. (2000). Thyroid disease and female reproduction. Fertility and Sterility, 74(6), 1063-1070. https://doi.org/10.1016/s0015-0282(00)01589-2
Menstrual problems are less common in thyroid disease than once taught
Fewer women with thyroid disease have menstrual problems than older reports described, according to a 2000 review of studies found by MEDLINE search. About 2 out of 10 women with an overactive or underactive thyroid had menstrual changes in the author's recent studies. Some older series reported 5 to 7 out of 10.
Key Findings
In 214 thyrotoxic patients, 21.5% had a menstrual disturbance, against 8.4% of normal controls and 50 to 60% in some older series. Most thyrotoxic women remain ovulatory by endometrial biopsy.
Among 171 hypothyroid patients, 23.4% had irregular cycles, against 50 to 70% in previous studies. The most common type was oligomenorrhea (infrequent periods), at 42.5%.
Failed ovulation is commonly associated with severe hypothyroidism. Women with mild hypothyroidism can ovulate and conceive, though in the past those pregnancies were often associated with abortions, stillbirths, or prematurity.
Among 814 women with thyroid cancer, the fertility rate was 23 per 1,000 fertile females per year in 627 treated with 131I and 19 in 187 untreated (P value 0.39).
Among 2,113 pregnancies conceived after 131I for thyroid cancer or remnant ablation, stillbirth, low birth weight, preterm birth, congenital malformation and first-year death were not significantly different from pregnancies conceived before therapy.
Interpretation
This 2000 review examined MEDLINE studies on thyroid disease and menstrual cycles. The lower rates of menstrual change come from two earlier studies that each used normal control groups. The author says earlier diagnosis and milder disease explain the drop from older reports. Miscarriage reached 40% in 10 women treated with 131I in the year before conception. Recent studies suggest pregnancy loss in mild hypothyroidism is less common than earlier reports described. The author notes that small patient numbers and the lack of internal controls limit the 131I pregnancy studies. The findings support larger studies on thyroid function and fertility.
RRM Context
Restorative reproductive medicine seeks the cause of a cycle problem. The review says mild thyroid underactivity may matter more in "unexplained" infertility, especially when the luteal phase is inadequate. The author says such patients warrant an in-depth thyroid check. Unexplained infertility has no diagnosis yet.
Our editorial summary of this paper, not the article's abstract.
Abstract
Objective
To review the menstrual function and fertility in thyroid disease, mainly in hyperthyroidism and hypothyroidism. Also to register the consequences of (131)I therapy, which is used widely in the treatment of Graves' disease and thyroid cancer, on subsequent pregnancies and on fertility in these patients.
Design
A MEDLINE computer search was used to identify relevant studies. The type of menstrual disturbances and the status of fertility were recorded from all the studies found. Also, the fertility and genetic hazard of female patients with Graves' disease and thyroid cancer who were treated with (131)I were registered.
Results
Both hyperthyroidism and hypothyroidism may result in menstrual disturbances. Menstrual abnormalities are less common now than in previous series. In a recent study, we found that only 21.5% of 214 thyrotoxic patients had some type of menstrual disturbance, compared to 50 to 60% in some older series. The most common manifestations are hypomenorrhea and oligomenorrhea. According to the results of endometrial biopsies, most thyrotoxic women remain ovulatory. Moreover, the genetic hazard incident to radioiodine therapy in Graves' disease and thyroid carcinoma is very small; exposure to (131)I does not cause reduced fecundity, and the risk of loss of fertility is not a contraindication for its use in these patients. mIn hypothyroidism, the frequency of menstrual irregularities has very recently been reported to be 23.4% among 171 hypothyroid patients studied. This is much less than that reported in previous studies, which showed that 50 to 70% of hypothyroid female patients had menstrual abnormalities. The most common manifestation is oligomenorrhea. Severe hypothyroidism is commonly associated with failure of ovulation. Ovulation and conception can occur in mild hypothyroidism. These pregnancies are, however, often associated with abortions, stillbirths, or prematurity. The latter may be of greater clinical importance in infertile women with unexplained infertility.
Conclusions
These new data, mainly concerning menstrual abnormalities in hyperthyroidism and hypothyroidism, are inconsistent with what is generally believed and written in the classic thyroid textbooks and indicate that such opinions should be revised.
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