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Hypothyroidism during pregnancy can result in serious health issues for both mother and child if it's left untreated.

Gestational period is a time of great changes in a woman's body, including fluctuations in hormone levels. When it comes to thyroid hormone, it's usually lower during pregnancy (between 0.4 and 4.0 mI/L). If thyroid-stimulating hormone increases over 2.5 to 3.0 mI/L, we talk about mild hypothyroidism also called subclinical underactive thyroid.

Hashimoto's disease is the leading cause of underactive thyroid in pregnant women. Hashimoto's thyroiditis makes the body fight against thyroid gland cells, making the gland weak and without cells to meet the body's needs for thyroid hormone.

Having underactive thyroid during pregnancy can lead to many health issues if the condition is untreated. These are all serious problems such as abrupted placenta, membrane rupture, and even death of both mother and the baby. Luckily, women nowadays take much more care of their bodies than before and hypothyroidism is rarely left untreated.

Women who knew about their condition before pregnancy are often prepared well for what's coming and know a lot about therapy options. Hypothyroidism in pregnancy is hard to diagnose because symptoms such as tiredness or significant weight gain can be part of normal pregnancy. Here are a few more symptoms of hypothyroidism in pregnancy:

  • Swollen face and extremities
  • Bloating
  • Feeling constipated
  • Muscular pain
  • Sensitivity to cold
  • Arrhythmia
  • Trembling hands
  • Being easily distracted
  • Problems with memory

An underactive thyroid can be diagnosed with blood testing, as well as a screening of the levels of thyroid-stimulating hormone prior to pregnancy or as soon as after your doctor establishes the pregnancy. You should get screened if you have goiter, family history of underactive thyroid, if you experience symptoms similar to those of thyroid disease, and especially if you were treated for hypothyroidism in the past.

What happens if you don't treat your underactive thyroid

Thyroid disease can be dangerous for pregnant women and their babies if not treated right, especially if not treated at all. Here are some dangers of not treating your hypothyroidism:

  • Anemia (mothers tend to have low red blood cell count)
  • Muscular weakness and pain
  • Pre-eclampsia
  • Risk of heart diseases
  • Placental malformations
  • Postpartum bleeding
  • Newborn with low birth weight
It's important to note that these symptoms occur mostly in women with severe cases of underactive thyroid, and those who don't treat it during pregnancy. In most other women with thyroid disease, symptoms are mild and similar to those experienced during any other pregnancy.

Babies are at risk of thyroid disease too

Women with thyroid disease often give birth to children with so-called congenital hypothyroidism, where they thyroid gland has no function at birth. Because thyroid-stimulating hormone is extremely important for proper neurological and cognitive development, it's important to recognize this problem in newborns and start the treatment immediately.

All possible abnormalities that this condition can bring can be prevented if the baby is treated promptly. It's good to know that in the U.S. and many parts of the world all newborns are screened for congenital thyroid disease soon after birth and those who need it are urgently given the necessary treatment.

If thyroid disease is not treated, it becomes severe after a while and it can affect the brain development of an infant. A simple thing such as iodine deficiency can cause hypothyroidism which will affect the baby as well. You have to be careful and treat thyroid disease, especially during pregnancy because research has shown that even mild thyroid disease can lead to neurological and cognitive abnormalities in offspring.

How to treat underactive thyroid during pregnancy?

If your thyroid gland can no longer produce the necessary amounts of hormone, it is easily done with replacement hormone levothyroxine. It's a synthetic form of a hormone that reminds a lot to thyroxine (T4), a naturally occurring hormone in our bodies. Taking replacement therapy is safe during the gestational period and won't harm the baby in any way.

Your physician knows best how much of the replacement hormone you'll need. It's important to monitor levels of the thyroid-stimulating hormone every few weeks in the first two trimesters, and at least once in each trimester.

Pregnant women with mildly underactive thyroid often even don't need the treatment. Those women who had hypothyroidism therapy prior to pregnancy probably won't have to increase the dose of levothyroxine, but your doctor should check the situation anyway.

Experts recommend adjusting the dose of levothyroxine so the thyroid-stimulating hormone level is under 2.5 milli-international units per liter before getting pregnant. Apparently, this decreases the chances of TSH spiking up within the first three months of pregnancy.

If you're planning on getting pregnant it's important to confirm pregnancy in the early stadium because the dose of levothyroxine should be adjusted to protect the baby, as well as a woman's health.

Most women don't have problems during pregnancy if the lacking thyroid hormone is replaced quickly and hypothyroidism is treated the whole time during pregnancy.

Experts endocrinologist claim it's best to keep your levels of thyroid-stimulating hormone between 0.1 and 2.5 milli-international units in the first trimester of pregnancy, 0.2 to 3 mIU/L in the fourth, fifth and sixth month of pregnancy, and 0.3 to 3.0 during the last trimester. When a woman gets her pregnancy confirmed, it's usually already time to double up the dose of a hormone replacement therapy.

When a woman with any type of autoimmune condition gets pregnant, she is at high risk of developing thyroid condition. This is why it's crucial to monitor these women for any possible spikes in thyroid-stimulating hormone. Nutrients such as calcium or iron that are often a part of recommended prenatal care may affect the absorption of levothyroxine, so it's recommended to take them a few hours apart of taking your hormone replacement therapy.

Besides thyroxine (T4), the thyroid gland produces another hormone – triiodothyronine (T3), which is unlike T4 unable to get to baby's brain in early stages of pregnancy, so all T3 that baby might need comes from T4. Even though T3 is put in thyroid drugs of animal origin, it's of no use to the baby's brain, so you should avoid this type of therapy and specifically ask your doctor for T4 during pregnancy.

Dangers of treating underactive thyroid while pregnant

There's research that supports the treatment of underactive thyroid with TSH during pregnancy. Researchers recommend that taking anywhere from 4.1 to 10 mIU/L decreases chances of pregnancy loss by 38 percent. Despite of these studies, there's research claiming that treating hypothyroidism with hormone replacement therapy may increase chances of gestational diabetes, hypertension that may lead to pre-eclampsia, and ever preterm delivery.

This research suggests that cases of subclinical hypothyroidism where the thyroid-stimulating hormone is in the range between 2.5 to 4.0 mIU/L might be best to left untreated. Of course, these findings aren't official and additional research is needed. It's best to discuss your options with a physician who knows you and your family history well.

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