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Hypothyroidism and Pregnancy
Frequently Asked Questions About Being Pregnant With an Underactive Thyroid

by Mary Shomon

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Congratulations….you're pregnant! Whether this is your first child or fifth, whether conception took you many years or a few months, pregnancy is a marvelous, awe-inspiring time in a woman's life. Your hypothyroidism -- an underactive thyroid -- doesn't change that, although it may make your pregnancy slightly more complicated than someone without a thyroid disorder. It's heartening to note, however, that most women with thyroid disease are able to have an uneventful pregnancy and healthy baby. I did myself, back in 1997!

The following "Questions and Answers" will help you better understand hypothyroidism and pregnancy.

Am I considered hypothyroid?

First, let's define hypothyroid, for the purposes of this discussion. If you have the autoimmune disease Hashimoto's Thyroiditis, and have been diagnosed as having related "hypothyroidism" -- an underactive thyroid -- you are considered hypothyroid. If you have thyroid nodules or goiter, and have been told you have an elevated TSH level and are taking thyroid hormone replacement, then you are considered hypothyroid. If you have had Graves' disease or hyperthyroidism, and have had radioactive iodine (RAI) or surgery of the thyroid, and are now taking thyroid hormone replacement, then you are considered hypothyroid. And if you have had any or all of your thyroid surgically removed, due to thyroid cancer, nodules, or goiter, and are taking thyroid hormone replacement, then you are considered hypothyroid.

I just took a home pregnancy test and found out I'm pregnant! I'm thrilled, but a little nervous, since I was just diagnosed with hypothyroidism last year. What can I do to ensure my health - or my baby's health - doesn't suffer? Do I need to take another TSH test?

The key in dealing with your thyroid condition during pregnancy is close monitoring of your TSH and T3 and T4 levels and compliance with your treatment regimen. Many guidelines say that a pregnant woman with hypothyroidism should have her thyroid function checked during each trimester. In particular, it's known that the thyroid hormone dosage requirement can increase in the early part of pregnancy due to the increased estrogen levels of early pregnancy. Since many women aren't even sure that they are pregnant until four to six weeks after the last menstrual period, many women don't even get in to see their doctors -- and test their thyroid function -- until the first trimester is more than half over.

Interestingly, if you call to schedule a first visit with an obstetrician, they often aren't that concerned about getting you in that early in the pregnancy, because they may not be particularly knowledgeable about hypothyroidism in pregnancy.

My suggestion is that you try to make sure that you find out you are pregnant as early as possible, and get in for thyroid testing as soon as possible after finding out you are pregnant.

I tested positive in a home pregnancy test 10 days post conception, had a blood test to confirm pregnancy at 3 weeks post conception, and was seen by a ob-gyn at a little less than 5 weeks. At that point, my TSH had already risen from 1.2 to almost out of the normal range. My dosage was adjusted. I was tested again a second time at around 9 weeks, and again, my TSH had risen, and a dosage adjustment was required.

Why is it so important that I see the doctor now? I'm only a few weeks pregnant. Do I still need to take my thyroid hormone replacement medication?

Yes, you must continue to take your thyroid hormone replacement (i.e., Synthroid, Levoxyl, Levothroid, Armour, Thyrolar) and it's extremely important that you do, now and throughout the rest of your pregnancy. You are your baby's only source of source of thyroid hormones at this point - your baby's thyroid gland isn't fully functional until after 12 weeks of pregnancy. If you don't have sufficient thyroid hormones, you are at an increased risk of miscarriage, and your baby is at increased risk of developmental problems.

I've just been surfing the Web reading about thyroid disease and pregnancy, and what I've read can be frightening -- fetal abnormalities, risk of low IQ, possible developmental problems, recurrent miscarriages, risk of stillbirth and premature labor. Now I'm nervous. Am I taking a big risk in being pregnant?

No, not necessarily. The operative word for these concerns is UNTREATED thyroid disease. Yes, it's true, for example, that babies born to mothers with untreated hypothyroidism are almost four times more likely to have lower IQs and learning difficulties, according to a study reported on in the New England Journal of Medicine in 1999. The study went on to note, however, that children whose mothers were undergoing treatment for an underactive thyroid scored almost the same as children born to mothers with normal thyroid function.

Chances are since you are reading this article, you know you are hypothyroid and thereby know to take the proper precautions. Having your doctor check not only your TSH levels, but also T4, is vital. Normal TSH, but low Free T4 (FT4), can be problematic during pregnancy. According to research presented at the June 2000 Endocrine Society conference ("Maternal Thyroid Function During Early Pregnancy and Neurodevelopment of the Offspring," June 21, 2000, Clinical Symposium: Impact of Maternal Thyroid Function on the Fetus and Neonate) there is increasing evidence that even normal FT4 levels that fall into the lowest tenth percentile during the early stages of pregnancy can be associated with poor infant development. Low-normal FT4 is not defined as maternal hypothyroidism when TSH is normal, but these outcomes indicate that screening and treatment for thyroid problems may be warranted in all women.

The study concluded that women with a low normal FT4 -- in the lowest 10th percentile at 12 weeks' gestation -- are at risk for children with developmental delay. Further, the researchers found that "TSH, during early gestation, seems to be without any value to pick up these women at risk."

So, you may wish to consult with a cutting-edge endocrinologist or thyroid expert who is willing to monitor not only your TSH but your FT4 levels throughout your pregnancy.

But generally, the best things you can do to ensure a healthy outcome is comply with your treatment, make sure your endocrinologist and/or ob-gyn truly understand hypothyroidism and pregnancy, ask questions of your doctor, and finally, relax. According to thyroidologist Dr. Sheldon Rubenfeld, M.D., a woman should approach pregnancy with the mindset that thyroid disease is not likely to be a problem in her pregnancy. Pre-existing nodules and goiters, for example, don't tend to create any additional concern, and treated hypothyroidism adds only a slight risk during pregnancy.

Will hypothyroidism make my pregnancy harder, or more dangerous?

In terms of whether being pregnant is harder when you're hypothyroid, most people I've talked to who have autoimmune hypothyroidism say they've actually felt better while pregnant. While pregnant, I have to say, I felt the best I'd been since being diagnosed hypothyroid. Naturally, I had the typical tiredness most pregnant women experience, but it was a different feeling, not the bone-numbing fatigue and brain fog I'd had with untreated hypothyroidism, but more of a sleepiness that was relieved by naps and nighttime sleep. My allergies were near non-existent, I didn't get a single cold, flu or other ailment. I've heard doctors speculate that some women with autoimmune diseases have immune systems that function almost perfectly during pregnancy, and I seemed to be one of them. After several fluctuations and dosage adjustments the first trimester, I had my thyroid tested every two months or so, and it varied no more than a few tenths of a point, requiring no adjustment in my medication throughout the entire pregnancy. It's never been so stable before, or since.

My main pregnancy concern? More weight gain that I'd have liked, and a borderline blood sugar problem that the doctor said wasn't gestational diabetes, but was close to it, late in the pregnancy. I ate very healthily -- I thought -- but looking back, I realize my diet was very heavy in carbohydrates and fruits. I think that hypothyroidism's tendency to give some people an exaggerated insulin response and near diabetic blood sugar levels may make some pregnant women with hypothyroidism more susceptible to borderline or full-blown gestational diabetes. If I have another baby, I will definitely follow a low-glycemic diet suitable for more strictly controlling blood sugar. Luckily, I had a pretty non-eventful pregnancy and an easy c- section (my baby was breech) and my daughter was born a healthy 8 1/2 pounds.


I'm taking Synthroid as well as my prenatal vitamins. Should I take them at the same time, with a meal, or separately, or on an empty stomach, or what? I asked my doctor, but she didn't know.

In my case, when I called to schedule that first appointment, the nurse told me to start taking an over-the-counter prenatal vitamin with iron right away. What the nurse didn't tell me then, or the doctor didn't mention at any point during my pregnancy, is something few obstetricians or even endocrinologists will tell you about prenatal vitamins. Iron, whether in prenatal vitamins, or as separate supplements, can interfere with proper absorption of thyroid hormone, causing you to get less thyroid hormone than you need.

This is a problem anytime, but particularly of concern during pregnancy, when you want to make extra sure you get enough thyroid hormone at all times. The solution is simple. You need to take the thyroid hormone at least two to three hours apart from the prenatal vitamin or iron-containing supplement. This allows you to get full absorption of the thyroid hormone without interference from the iron.

While we're on the subject of the iron in vitamins, it's worth looking at a few other things that can interfere with proper absorption of thyroid hormone. Eating a high-fiber diet and taking antacids are two activities more common during pregnancy. Both activities, however, can have an impact on absorption of thyroid medication, and thus, affect thyroid function and levels during pregnancy. To maximize absorption and make sure the proper amount of thyroid hormone is processed, doctors recommend that you take thyroid hormone without food, on an empty stomach, at least two hours after or one hour before eating, and do not take a prenatal vitamin with iron within two to three hours of taking your thyroid hormone.

Consistency is also important. If for some reason, you can't take your pill on an empty stomach, it's better to decide to take your thyroid pill every day with food, than miss taking it or take it erratically - some days with food, some days without. You may stabilize at a slightly higher dosage than if you weren't taking your pill with food, but you'll get to the right dosage.

I really want to have a drug-free pregnancy, and I'm suspicious of anything that might hurt the baby. Should I stop taking my thyroid medication?

Absolutely not! Your instincts are good, as most drugs -- prescription or over-the-counter -- are not recommended during pregnancy. But thyroid hormone is NOT a drug you should stop. To not take your thyroid hormone is a danger to your health and your pregnancy. Thyroid hormone, in proper doses, is replacing something your body needs in order to maintain a healthy pregnancy. The greatest danger is to think that taking thyroid hormone is bad for your baby, and discontinuing your thyroid hormone replacement. Thyroid hormone is one of the few drugs in pharmaceutical category "A" (Low Risk) for pregnant women. Studies in pregnant women show that when taken in the proper dosage, there are no adverse effects on the fetus.

I plan to breast-feed my baby, and I'm wondering if I'll be able to, since I'm hypothyroid. Can I safely take my thyroid medication while nursing?

Because only trace amounts of thyroid hormone medication -- when taken in proper doses -- are excreted in breast milk, yes, you can safely nurse your child. Thyroid disorders can pose special challenges to breast-feeding, but in most cases, women with thyroid problems can nurse. In no way should you stop, or limit your medication, in order to nurse. In fact, you have to have proper thyroid hormone levels to ensure enough breast milk for your baby. For more in-depth information, please read:
Breastfeeding and Thyroid Disease, Questions and Answers

I have Hashimoto's hypothyroidism. Does that mean my baby will too?

It's pretty rare, but it can happen. However, since Hashimoto's typically doesn't appear until the second decade of life, it's not likely to be seen in infants. Congenital hypothyroidism appears in one per 4000 or 5000 newborns. If thyroid therapy is started during their first three months, most of these children will have normal intellectual development. Untreated, however, their hypothyroidism can lead to serious mental and physical impairment. In the U.S., all newborns are required to be tested for low T4 levels; the test is typically done along with the heel stick for PKU (phenylketonuria). But you may want to just double check at the hospital, or with your child's pediatrician at her/his first post-hospital visit, to make sure the thyroid check was performed, as occasionally, tests are forgotten.

Read the Thyroid Guide to Fertility, Pregnancy and Breastfeeding Success

Researcher/writer Laura Horton contributed to this article.

Sticking Out Our Necks and this website are © Copyright Mary Shomon, 1997-2003. All rights reserved. Mary Shomon, Editor/Webmaster
All information is intended for your general knowledge only and is not a substitute for medical advice or treatment for specific medical conditions. You should seek prompt medical care for any specific health issues and consult your physician or health practitioner before starting a new treatment program. Please see our full disclaimer.