Hypothyroidism (“low” thyroid) can cause menstrual abnormalities, infertility, increased risk of miscarriage, pregnancy complications – for both mother and baby. Hypothyroidism is usually diagnosed by an increase in thyroid stimulating hormone (TSH) levels (> 2.5 mIU/mL) and low levels of free thyroxine (FT4). Details of the impact of the thyroid gland on female reproduction have been discussed by me in a previous blog.
Sub-clinical hypothyroidism is a condition where the TSH level is elevated but the patient is without any symptoms and FT4 levels are normal. It occurs in 4% – 8.5% of the general population and significantly higher in patients with infertility.
It is a well-established fact that thyroid requirements increase during pregnancy. Sub-clinical hypothyroidism may therefore worsen in pregnancy. It is generally accepted that a symptomatic patient with hypothyroidism should be treated with a thyroid pill (LT4; levothyroxine; Synthroid). But, what about patients with elevated TSH levels that are otherwise asymptomatic? Does untreated sub-clinical hypothyroidism affect IVF pregnancy rates? Does treating it with levothyroxine (LT4; Synthroid) improve IVF pregnancy rates? Chung-Hoon Kim and co-workers from the University of Ulsan, College of Medicine, Asan Medical Center, Seoul, South Korea recently addressed these very questions (Fertil Steril2011; 95:1650–4).
They investigated 64 infertile patients with subclinical hypothyroidism (defined as an elevated serum TSH level >4.5 mIU/L with a normal FT4 level and without frank symptoms of hypothyroidism). Patients were randomized into an LT4 treatment group or control group. For the LT4 treatment group, 50 mg LT4 was administered from the first day of controlled ovarian stimulation for IVF/ICSI.
There were no differences in patient characteristics between the two groups. Total dose and days of recombinant human FSH used for controlled ovarian stimulation were also similar. The number of grade I or II embryos was significantly higher in the LT4 treatment group than in the control group. There was no significant difference in the clinical pregnancy rate per cycle between the two groups. However, the miscarriage rate was significantly lower in the LT4 treatment group than in the control group. Embryo implantation rate (26.9% vs. 14.9%) and live birth rate (53.1% vs. 25%) were significantly higher in the LT4 treatment group. The TSH level on day of hCG injection was 2.9 + 1.0 in the treated and 6.8 + 1.9 mIU/mL in the control group indicating that the TSH level can be normalized very quickly in this group of patients.
The authors conclude that LT4 treatment can improve embryo quality and pregnancy outcome in subclinical hypothyroid women undergoing IVF/ICSI. Therefore, LT4 treatment should be considered in subclinical hypothyroid patients planning IVF/ICSI, and pregnant patients after IVF/ICSI should be treated with an adequate dose of LT4 throughout the whole pregnancy period.
At InVia Fertility Specialists, we routinely check TSH levels. According to current recommendations by the American Association of Clinical Endocrinologists and American Thyroid Association Task Force guidelines; TSH levels should be maintained < 2.5 mIU/mL. This paper confirms that we have been managing our patients appropriately and that no change in our current treatment protocols in needed.
The impact of hypothyroidism and its management during pregnancy will be discussed in a follow up blog.
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