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Becoming a Mother with Hashimoto's Disease

Can Autoimmune Thyroiditis Affect Your Pregnancy?

Jun 8, 2009 Sarah Tomley

All forms of hypothyroidism affect pregnancy, but Hashimoto's responds uniquely to the body's altered state and new demands.

Pregnancy always affects the thryoid, whether you are pregnant or not. Two pregnancy hormones – hCG (human chorionic gonadotropin) and estrogen – affect the levels of thyroid hormone in the blood during a healthy, straight-forward pregnancy, so thyroid function tests do show some level of change (decreased TSH) without indicating a problem. The thyroid may even increase slightly in size in response to new demands from the body. Generally, the thyroid is considered to be functioning properly if the TSH, Free T4 and Free T3 remain at normal, healthy levels, and any thyroid size increase is less than 10 per cent.

How Will Having Hashimoto’s Affect my Pregnancy?

Firstly, you’re more likely to have trouble getting pregnant, as recent data suggests that the presence of the thyroid autoantibodies found in Hashimoto's disease may reduce the chance of conception.

Secondly, the course and severity of Hashimoto’s tends to alter during pregnancy and in the postpartum period. Your thyroid’s response to a fluctuating immune status (because of the baby), combined with changes in thyroid use during pregnancy, means that any Hashimoto’s treatment will probably need adjustment. Your hypothyroidism (see below) may worsen, or actually improve. (5)

Thirdly, watch out for complications after you’ve given birth. Women with Hashimoto’s have an increased risk of developing post-partum thyroid dysfunction; in one recent study more than 47 per cent of women who tested positive for thyroid peroxidase antibodies in early pregnancy developed postpartum thyroid problems. (3) It seems that pregnancy may tip the balance, from having peroxidase antibodies to actually developing thyroiditis, and the risk is proportionate to the number of antibodies: the higher the antibody levels, the higher the risk of developing thyroiditis. If you feel “blue” after the birth, be sure to get your thyroid levels checked.

What Can Go Wrong With my Pregnancy if I’m Hypothyroid?

Hashimoto’s is the most common cause of hypothyroidism, and of all women with hypothyroidism, around 2.5 per cent will develop a slightly elevated TSH (greater than 6) while 0.4 per cent will experience higher levels (TSH greater than 10).

In cases where severe hypothyroidism is untreated, or inadequately treated, hypothyroidism during pregnancy has been associated with:

maternal anemia (low red blood cell count)
myopathy (muscle pain, weakness)
congestive heart failure
pre-eclampsia
placental abnormalities
low birthweight babies
miscarriage
stillbirth
postpartum hemorrhage (bleeding).

But note that these symptoms manifest in severe, untreated forms of hypothyroidism. The disease is easily treatable, and women with mild hypothyroidism are not likely to experience any symptoms or complications.

I’ve Got Hashimoto’s and I’m Pregnant – What Should I Do?

Women with any form of established hypothyroidism should have a TSH test as soon as they know they are pregnant.

If you are already taking thyroid hormone medicine (levothyroxine), the dose will probably need to be increased – to raise levels of the hormone in the body just as they would be raised in a healthy body. Levothyroxine requirements may raise by 25–50 per cent. You’ll need to have thyroid function tests every 6-8 weeks during pregnancy, and re-check your levels 4 weeks after any change in thyroxine dosage. After the birth, most women return to their pre-pregnancy dosage level.

If you have tested positive results for thyroid receptor–stimulating antibodies or are taking ATDs, you’ll need to undergo fetal ultrasonography at least monthly after you reach the 20th week of your pregnancy.

If your TSH is normal, and you are not currently undergoing treatment, it’s unlikely that you’ll need any during pregnancy. But always make your healthcare provider aware of your condition, so they can watch for potential complications, such as pre-eclampsia, and test your thyroid levels as necessary.

After the Birth

All women with a past or current history of autoimmune thyroid disease should have their thyroid antibody values checked after the baby is born. It may help to know that once you’ve had your baby, you can breastfeed while on Levothyroxine – the drug does enter the breastmilk, but in levels that are too low to alter the baby’s thyroid function or alter any of its blood tests. (4)

Iodine and Hashimoto’s Thyroiditis

NOTES

The American Thyroid Association, “Thyroid Disease and Pregnancy”, Patient Brochure 2008.
“Transient Graves' hyperthyroidism during pregnancy in a patient with Hashimoto's hypothyroidism” Lu R, Burman KD, Jonklaas J.; Thyroid. 2005 Jul;15(7):725-9.
“Management of high-risk pregnancy”, Queenan & Spong, Wiley-Blackwell, 2007. p.187
"Management of high-risk pregnancy”, Queenan & Spong, Wiley-Blackwell, 2007, p.188
“Autoimmune Thyroid Disease and Pregnancy”; Dotun A Ogunyemi, MD, Associate Professor of Obstetrics and Gynecology, David Geffen School of Medicine at UCLA; e.medicine 3 June 2009.

The copyright of the article Becoming a Mother with Hashimoto's Disease in General Medicine is owned by Sarah Tomley. Permission to republish Becoming a Mother with Hashimoto's Disease in print or online must be granted by the author in writing.