Thyrotropin and thyroid hormone variability across menstrual cycle in healthy females.

Abstract

BACKGROUND-This is the first attempt to assess the variability in the circulating concentration of TSH, TT3, TT4 across menstrual cycle in regularly menstruating healthy females free of clinical thyroid dysfunction from this region of the world . As it is well known that, estrogen increases TBG by several mechanisms including increased hepatic synthesis of TBG and diminished metabolic clearance rate of TBG due to its enhanced sialyation.

AIMS AND OBJECTIVE -  To assess the presence and magnitude of variability in thyrotropin and thyroid hormone levels across menstrual cycle.

MATERIALS AND METHODS -The study was conducted over a period of 18 months (2017-2018). The study subjects were recruited from among the hospital staff and other acquaintances, and their family members. Only females 20-45 years who were regularly menstruating (cycle length of 28+/-4 days) and who gave consent to participate in the study were recruited.  The follicular phase sample was collected on day 3-5 of the cycle. The luteal phase sample was taken on day 2-4 after the estimated day of ovulation. Serum concentrations of TSH, T3, and T4 were measured by D X1800, Beckmann counter chemilumiscence analyzer following the manufacturer’s protocol.

RESULTS AND OBSERVATIONS- The mean serum TSH concentrations were significantly higher during the luteal phase than during the follicular phase of the menstrual cycle; while the mean serum levels of TSH were 2.58µg/dl in the follicular phase, they were 3.37µg/dl during the luteal phase (p < 0.001). However, there were no statistically significant differences between the mean concentrations during the follicular and luteal phases of the menstrual cycle either for total T3 or total T4.

SUMMARY AND CONCLUSION-The mean serum TSH concentration in the luteal phase was significantly greater than that in the follicular phase (p <0.001); the mean serum concentrations of total T3 and total T4 in the follicular and luteal phases of menstrual cycle ,however, were comparable (p ˃0.05 for both).The mean TSH, total T3, and total T4 concentrations in the luteal phase were found to be unaffected by the age, habitat, or the body mass index of the study subjects.