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.
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
- Feeling constipated
- Muscular pain
- Sensitivity to cold
- 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
- Risk of heart diseases
- Placental malformations
- Postpartum bleeding
- Newborn with low birth weight
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.
How to treat underactive thyroid during pregnancy?
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.
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.
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.