Disturbances of menstruation in hypothyroidism

Most thyroid textbooks describe hypothyroidism resulting in changes in the length of the menstrual cycle and in the amount of bleeding. Our experience at a busy thyroid clinic had given a picture which differs from that presented in the literature. The aim of this study was to determine the frequency and type of menstrual irregularities in premenopausal hypothyroid patients.

We investigated the menstrual history, starting 6 months before the discovery of the disease, in 171 female premenopausal hypothyroid patients and 214 normal controls, with similar age and body mass index (BMI).

TSH, TT4, TT3 and thyroid antibodies were measured by radioimmunoassay, while BMI was calculated from the ratio of body weight in kg to height in m2.

Of the 171 hypothyroid patients, 131 (76.6%) had regular cycles and 40 (23.4%) irregular periods. Oligomenorrhoea and menorrhagia were the most common features in the latter group. No difference in BMI was found between the patients with or without menstrual abnormalities, or between patients and controls. TSH, TT4 and TT3 levels did not differ between patients with normal and abnormal menstruation. Forty-six (26.9%) out of 171 patients had subclinical hypothyroidism (group A), 42 (24.6%) mild hypothyroidism (group B) and 83 (48.5%) severe hypothyroidism (group C). Thirty-seven from group A (80.4%), 32 from group B (76.2%) and 62 from group C (74.7%) had normal periods. These differences were not statistically significant. Eighty-eight (88.9%) out of 99 patients in whom thyroid antibodies were measured had positive titres. Nineteen (21.6%) of the patients with positive thyroid antibodies had menstrual irregularities. This percentage did not differ from that found in the whole group of patients (23.4%). Out of 214 normal controls, 196 (91.6%) had normal menstruation and 19 (8.4%) irregular cycles. The latter group included mainly women with oligomenorrhoea.

These data demonstrate that hypothyroidism in women is less frequently associated with menstrual disturbance than was previously described. Also, menstrual irregularities tend to be more frequent in sever hypothyroidism in comparison with mild cases, although this finding was not statistically significant. Oligomenorrhoea and menorrhagia are the most common menstrual disturbances.