Top 10 facts about the thyroid gland and female reproduction

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Slide11) The thyroid is a butterfly-shaped gland in the base of your neck just below the Adam’s apple.  It produces several hormones.  The most important is thyroxine (T4), which controls the body’s metabolism.  It is critical that the thyroid functions normally.  If there is too much (hyperthyroidism) or too little T4 (hypothyroidism), the body does not function normally.

2) Thyroid dysfunction is fairly common and affects almost 1% of women.  According to The Thyroid Foundation of America, there are as many as 8 million women in America with untreated thyroid disorders.  For those of reproductive age, infertility or miscarriage may be the first sign that something is wrong.  In this blog we will discuss the impact of hypothyroidism (the most common thyroid disorder) on female reproductive function.

3) What are the symptoms of hypothyroidism?  The slowed-down metabolism associated with hypothyroidism can manifest as fatigue, dry skin, constipation, heavier periods, weight gain, decrease in appetite, lethargy, depression, cold intolerance, or muscle aches.

4) How does hypothyroidism cause infertility?

  • Hypothyroidism can cause infertility by preventing ovulation—even when menstrual periods are occurring regularly.
  • Women with undiagnosed hypothyroidism who do conceive have an elevated risk of miscarriage. And even hypothyroid women who’ve already been diagnosed, treated, and stabilized with medication need to be monitored closely.
  • Some women with an underactive thyroid may experience elevated levels of prolactin, the hormone that induces the production of breast milk in postpartum women. Excess prolactin can make conceiving more difficult, again by preventing ovulation.
  • Hypothyroidism’s effects on metabolism can also bring on a condition known as luteal phase defect. The luteal phase is the second half of the monthly cycle, lasting from ovulation to menstruation. It is normally 12 to 16 days long. But if the luteal phase chronically runs shorter than ten days, then there will be fertility problems since the uterine lining can’t build up sufficiently for the embryo to implant, and it will be flushed from the body with the next menstrual period.

5) How is hypothyroidism diagnosed?  A simple blood test to measure thyroid stimulating hormone (TSH) level is used to diagnose hypothyroidism.  TSH works like a thermostat; it’s produced by the pituitary gland to regulate thyroid function.  An elevated TSH level is used to diagnose hypothyroidism.  It indicates that the pituitary gland is attempting to compensate for an underactive thyroid gland.

6) There’s also a blood test that checks for the presence of anti-thyroid antibodies. High levels of these antibodies are typical of a thyroid disease called Hashimoto’s Thyroiditis, which always results in hypothyroidism. Hashimoto’s Thyroiditis is classified as an autoimmune disease, because the body has essentially turned against itself, forming antibodies that attack the cells in the thyroid and slow down production of thyroid hormone. The gland itself may compensate by becoming enlarged.

7) In sub-clinical hypothyroidism, there are no symptoms.  The only way of diagnosing this condition is with a blood test (TSH level).  With elevated TSH levels, the quality of eggs retrieved is compromised.  This results in lower pregnancy rates.  It is therefore important that the TSH level be normalized prior to an IVF cycle.

8) What is the treatment of hypothyroidism?  Its simple.  We prescribe oral synthetic thyroid tablets (Synthroid, Levoxyl, Levothyroxine).  The goal is to treat with the lowest effective dose to maintain the TSH level close to (or just below) 2.5.  While establishing the correct dose can be quite easy in some individuals, others will fluctuate up and down before stabilizing.

9) The required thyroid dose increases by 30 – 50% during pregnancy.  TSH levels should be checked every 3 months during pregnancy and annually thereafter.  During pregnancy, an endocrinologist or an obstetrician that’s familiar with thyroid issues should monitor blood levels closely.  Uncorrected hypothyroidism can result in stillbirth.  I will often tell patients that taking their thyroid pill is as important (if not more) as taking their vitamins!

10) The good news is that among the various threats to fertility, thyroid disorders are arguably the easiest to identify and treat.

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8 Responses to Top 10 facts about the thyroid gland and female reproduction

  1. Commenter says:

    Hi Dr Karande – I have high antithyroid antiglobulin antibodies, I found out in January, they were 204uiml so I was advised to take 25mg of levothyroxine. In March my TSH was 2.43mul, it is now 0.86mul, T4 free is 1.16 & T3 is 0.8. I still however have the antithyroid antiglobulin at 159.8uiml and the clinic likes them below 60. So – should I be asking my Endo to up the dose of levothyroxine & most importantly, should I wait longer to embark on my next IVF/ICSI? First one failed so want to get it right the 2nd time round. I would like to know what you think, thanks.

  2. Commenter says:

    My TSH is 1.2 and my dr says it is normal. Above, they said they like to keep it around 2.5 I am not responding well to IVF meds.. they only retrieved 4 eggs. (age 39)
    I was on Armour thyroid, but the fertility dr told me to stop everything. I’m so confused. Also, I am in NYC, it is hard to find a Dr. that will treat a “normal” level TSH. Any suggestions?

    • There are plenty of good doctors in NY city.
      A TSH level of 1.2 is normal. We prefer to use Levothyroxine (Synthroid) and do not use Armour thyroid.
      I doubt your taking the medication had anything to do with your ovarian response.
      We have had plenty of pregnancies when 4 eggs have been retrieved.
      Perhaps you need to try again with an aggressive stimulation.
      We would welcome you as a patient at InVia.
      Dr V Karande

  3. Commenter says:

    Hi Dr.Karande I am 43 and my thyroid antibodies are 1500 I am on thyroxine my Tsh,T3 and T 4 are normal. What is the success rate of egg donor IVF cycle if I want to go for one. Please let me know. Are there any risk to the normal growth of the baby.


    • Hi Leena
      They are an incidental finding.
      I would not worry too much about the thyroid antibodies as long as your thyroid levels are normal.
      The pregnancy rate is around 70% per transfer. If you combine fresh + frozen transfers, the cumulative pregnancy rate from one cycle is even higher (? 80 – 85%).
      Wr would welcome you as a patient at InVia.
      Dr. V Karande

About Dr. Vishvanath Karande

Dr. Karande is Board Certified in the specialty of Obstetrics and Gynecology as well as the subspecialty of Reproductive Endocrinology and Infertility. He is a Fellow of the American College of Obstetricians and Gynecologists and Member of the American Society for Reproductive Medicine.

View all posts by Dr. Vishvanath Karande →

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