HOW DOES YOUR THYRIOD AFFECT FERTILITY AND PREGNANCY?

The thyroid is a small gland in your neck, just above your breast bone. The thyroid is controlled by the pituitary gland which releases thyroid stimulating hormone (TSH). This hormone tells the thyroid gland to release thyroid hormone

For over two thousand years the thyroid gland has been known to over or under-function.  Over the past few years we’ve recognised that an under-functioning thyroid (called hypothyroid) gland can have negative effect fertility and the health of children born to mothers with hypothyroidism.

Symptoms of hypothyroidism

If you are suffering from hypothyroidism you might experience

  • Low energy
  • Feeling cold
  • Thinning of the hair
  • Constipation

A low thyroid level can also increase blood pressure and can raise cholesterol. In women, hypothyroidism can disrupt monthly periods. It can also make it hard to get pregnant.

In women who do get pregnant, hypothyroidism can cause problems. For instance, it can increase the chances of having a miscarriage and of having a baby with low intelligence.

Hypothyroidism is common. It affects about 4% of reproductive aged women. If you are planning to get pregnant, struggling to get pregnant or are pregnant you should ask your doctor about getting your thyroid tested.

How is thyroid tested?

To determine whether your thyroid gland is functioning properly a blood test for thyroid stimulating hormone (TSH) is performed.  The normal TSH range is 0.3 to 5.5 mU/L.  Only levels above or below this range are a concern for most people.  For women trying to conceive or who are pregnant the normal TSH range is narrower, between 0.3 and 2.5 mU/L.

  TSH mU/L T4
Hyperthyroidism

 

<0.3

 

normal / high

 

Optimum for Fertility/Pregnancy

 

0.3 to 2.5

 

normal

 

Subclinical Hypothyroidism

 

<5.5

 

normal

 

Overt Hypothyroidism

 

<5.5

 

low

 

How is Hypothyroidism treated?

The good news is that if you have hypothyroidism taking thyroid replacement pill (e.g. levothyroxine) can improve all of these symptoms and make getting pregnant easier.  We also know that pregnant women with low thyroid can protect their baby by taking thyroid replacement pills.  Women who already take thyroid replacement pills before pregnancy usually need to increase their daily dosage by 30–50% when they are pregnant.

Hypothyroidism is a common disease with a fairly easy treatment. It can help you and your baby. It’s a good idea to discuss whether you should have your thyroid assessed by your physician.

Dr. Beth Taylor is co-director of Genesis Fertility Centre and Clinical Associate Professor at UBC. She completed her medical degree at Dalhousie University in 1998 and then moved to British Columbia to do her residency in Obstetrics and Gynecology at the University of British Columbia (UBC). She subsequently completed a fellowship in Reproductive Endocrinology and Infertility.

Dr. Taylor coordinates the UBC Obstetric & Gynecology residency program “Reproductive Endocrinology & Infertility” rotation. She is an active staff member at BC Women’s Hospital and Vancouver General Hospital and performs surgery at both of these centres.