Impact of hypothyroidism on pregnancy and the baby?

Dear Alice,

I am a bit confused about conceiving as I have a low thyroxine level. What impact might it have on pregnancy and the baby?


want to be a mother

Dear want to be a mother,

Thyroxine is the main hormone produced in the thyroid gland. If there’s too much or too little of this hormone in the body, it can result in hypothyroidism (due to especially low levels of thyroxine) or hyperthyroidism (due to especially high levels of the hormone). For more information on hypothyroidism, check out Hypothyroidism symptoms? Turning to your specific question, want to be a mother, low levels of thyroxine (and, in turn, hypothyroidism) may affect conception and pregnancy and it’s good to be aware of the potential health risks for both mother and baby. The good news is that treating hypothyroidism under the guidance of a health care provider can minimize these risks.

The ability to conceive varies across individuals due to all sorts of factors — one of them being hypothyroidism. In some, but not all people, having low levels of thyroxine may interfere with the ability to ovulate (when an egg is released from an ovary) — which is a necessary step in order to conceive. If the low levels of thyroxine occur due to an autoimmune disease or a pituitary disorder, there may be other risks to fertility as well. For those with hypothyroidism who are able to conceive and become pregnant, there are a number of conditions that they are at a higher risk for, including:

  • Anemia
  • High blood pressure
  • Pre-eclampsia
  • Premature birth
  • Postpartum thyroiditis (a contributing factor to postpartum depression)
  • Placental disruption (in which placenta becomes detached from inner wall of uterus)
  • Miscarriage

Fortunately, treating hypothyroidism — usually by taking the synthetic thyroid hormone levothyroxine — under the supervision of a health care provider may increase the likelihood of conception and a safer pregnancy. Depending upon the specific type of hypothyroidism, treatment during pregnancy may differ. People with overt (or full-blown) hypothyroidism taking levothyroxine are advised to continue taking it during pregnancy. Sometimes a change in dosage is necessary as determined by the health care provider. With the correct dosage, there should be no harm to the fetus, though regular monitoring by the health care provider is essential. Those with untreated subclinical hypothyroidism (which is characterized by a mildly underactive thyroid gland) require monitoring during pregnancy and some health care providers may recommend that they also take levothyroxine while pregnant. This is to make sure their condition does not progress to overt hypothyroidism. Untreated hypothyroidism during pregnancy can increase the risk of serious health consequences to both mother and baby, including:

  • Impaired neurodevelopment of the fetus
  • Mental impairment of baby
  • Acute respiratory distress syndrome of the newborn
  • Postpartum hemorrhage

Receiving appropriate treatment for hypothyroidism as early as possible, under the close supervision of your health care provider, is the best way to prevent health complications of the mother and the child. For more information on becoming and being pregnant, check out the Go Ask Alice! Pregnancy Options archive. Best of luck to you as you begin this exciting new journey!

Originally published Feb 20, 2015

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