[Thyroid and pregnancy]

Melatonin on hypothyroidism and gonadal development in rats: a review

We evaluated the evidence in research on the effects of melatonin on hypothyroidism and gonadal development. According to the World Health Organization, thyroid disorders due to iodine deficiency affect about 740 million people worldwide. Hypothyroidism is a thyroid dysfunction characterized by hypometabolism of the gland, with reduced or physiologically normal T3 and T4 serum levels, and high TSH level. This disorder occurs mainly in adult women in the reproductive phase, with a prevalence of 2% among the world's female population, with profound repercussions on gestation and fetal formation. During the gestational period, the thyroid is initially stimulated by high concentrations of human chorionic gonadotrophin; thus, maintaining maternal euthyroidism during pregnancy and lactation is fundamental for fetal growth and development. Besides, the hormones produced by this gland are involved in the formation of various organs, such as the skin, brain and gonads. Hypothyroidism is associated with several menstrual abnormalities, anovulation and hyperprolactinemia, resulting in a high rate of abortions, premature births, placental rupture, and weight-related neonatal deficits. In addition, there are studies showing that hypothyroidism can affect ovarian morphology (number of ovarian follicles) and testicular morphology (changes in the testicular-lumen epithelium). Melatonin is a hormone known to modulate the estrous cycle and pregnancy, and studies show that the exogenous application of melatonin increased T4 levels in female rats and controlled the decrease in T3 serum levels, reverting the sigs of hypothyroidism.

Effect of melatonin on gonad and thyroid development of offspring of hypothyroid pregnant rats

We investigated the effects of melatonin on rats with induced hypothyroidism during gestation as well as its effect on the development of the gonads of their offspring. Fifteen pregnant rats were divided into three groups: GC, rats without induced hypothyroidism; GH, rats with induced hypothyroidism; GHM, rats with induced hypothyroidism plus melatonin. Hypothyroidism was induced by oral administration of 6-propyl-2-thiouracil and melatonin was applied subcutaneously. Treatments were performed during gestation and lactation. For the matrices, we evaluated the number of pups, body weight gain, ovarian weight, thyroid weight, organosomatic index, thyroid stimulating hormone (TSH) dose and thyroid morphometry. For the pups, weight gain, TSH, weight, morphometry of the gonads and organosomatic index were analyzed, as well as the cell proliferation index. TSH was elevated only in the matrices of GH animals. Melatonin prevented reduction of ovarian and thyroid weight, number of pups, follicular diameter and thyroid epithelial proportion of the matrices with hypothyroidism. The offspring of rats of the GH group exhibited less body weight gain, gonad and thyroid weight, and gonad cell proliferation index compared to the offspring born of rats of the GC and GHM groups. Melatonin prevented the effects of maternal hypothyroidism on the offspring of rats.

Thyroid dysfunction in pregnancy: definition of TSH cut-off should precede the decision of screening in low-risk pregnant women

OBJECTIVE

To evaluate the frequency of elevated TSH in pregnant women of low risk for thyroid dysfunction.

SUBJECTS AND METHODS

TSH was measured in 838 pregnant women during the first trimester of gestation (from 6 to 14 weeks, median 9 weeks) and who were considered to be of low risk for thyroid dysfunction because they did not meet any of the following criteria: known or clinically suspected thyroid disease; history of head and neck radiotherapy; personal history of autoimmune diseases; family history of thyroid disease; history of abortion or prematurity.

RESULTS

The frequency of elevated TSH was 0.25%, 1.2% and 5.5% at cut-off values of 4, 3 and 2.5?mIU/l, respectively. These rates increase to 1.43%, 2.4% and 6.2% if cases of TSH> 2 mIU/l with TPOAb are included. TSH was undetectable in 18 women (2.1%), but only six (0.71%) had elevated T4.

CONCLUSIONS

The definition of a TSH cut-off that defines subclinical hypothyroidism (SCH) should precede the decision of screening pregnant women without any risk factors for thyroid dysfunction.