Thyroid Disorders Could Impact Functioning Ability of Ovaries

Akira Iwase, MD, PhD

A recent analysis is shedding light on the impact of thyroid disorders on the reproductive health of women.

A systematic review and meta-analysis of 9 trials published through October 2020, results of the study provide insight into the negative impact of hypothyroidism and thyroid autoimmunity (TAI) on ovarian reserves in women by demonstrating their influence on anti-Mullerian hormone (AMH) levels.

“Our age-stratified analysis demonstrated that thyroid autoimmunity and hypothyroidism possibly have different impacts on the ovarian reserve. It provides an important clue in determining how these conditions affect the development of ovarian follicles,” said senior author Akira Iwase, MD, PhD, of the Gunma University Graduate School of Medicine, in Japan, in a statement.

Citing previous research suggesting hypothyroidism and TAI were possibly associated with ovarian dysfunction, Iwase and colleagues from the Department of Obstetrics and Gynecology at Gunma University Graduate School of Medicine designed the current study as a systematic review and meta-analysis of studies published from inception to October 2020 from the PubMed, EMBASE, Web of Science, and Cochrane Controlled Trials Register databases. Their initial search yielded 244 articles, 32 underwent screening and were assessed for eligibility, and 9 were ultimately included.

For inclusion in the systematic review and meta-analysis, studies needed to evaluate ovarian reserve using serum AMH levels and contain women diagnosed with subclinical hypothyroidism, overt hypothyroidism, and/or TAI. For the purpose of analysis, the investigators' search included all prospective, retrospective, and cross-sectional studies. Investigators noted studies were excluded if they were published as an abstract, case report, or review or if they determined they failed to provide sufficient data.

Of the 7 studies included, 2 were retrospective studies, 4 case-control studies, and 1 cross-sectional study. A pair of studies compared TAI and control recruited adolescent females while the remaining 5 studies recruited adults. Investigators noted the studies included in the review showed comparable mean ages between case and control groups in each study.

Upon analysis, results suggested AMH levels were significantly lower in adults with thyroid antibodies (mean difference: -0.12 [95% CI, -0.18 to -0.06]; I²=0%). Further analysis assessing differences in AMH levels in euthyroid adolescents with and without thyroid antibodies indicated AMH levels were greater in the group of patients with thyroid antibodies (mean difference: 2.51 [95% CI, 1.82 to 3.21]; P <.00001, I²=0%).

In a secondary analysis, results indicated AMH tended to be lower in patients with SCH, but no significant difference was observed between the group (mean difference: -0.50 [05% CI, -1.11 o 0.11]; I²=0%). Additionally, an analysis of the difference in AMH between a group of patients with overt hypothyroidism and a control group, which was only reported in a single study, suggested AMH levels tended to decline with overt hypothyroidism but there was no significant difference between the groups (mean difference: -0.60 [95% CI, -1.34 to 0.14]).

“The current study indicates that TAI and/or hypothyroidism may affect the ovarian reserve. The opposite effects on AMH levels depending on the age suggest that TAI may be implicated in the depletion of follicles in adults following extensive activation of primordial follicles in adolescence. The results also suggest that early intervention in adolescent thyroid diseases may be helpful in maintaining the ovarian reserve,” wrote investigators.

This study, “Effect of hypothyroidism and thyroid autoimmunity on the ovarian reserve: A systematic review and meta-analysis,” was published in Reproductive Medicine and Biology.