Can Thyroid Conditions Cause Pregnancy Problems?

If you’ve been diagnosed with a thyroid condition before pregnancy or during prenatal care, you might be wondering how this affects your baby and your own health over the next nine months. The short answer is that thyroid disorders can create real risks during pregnancy, but with proper treatment and monitoring, most people go on to have healthy pregnancies and healthy babies.

Understanding what these conditions actually mean for you and your child can help you work more effectively with your healthcare team and feel more confident about the path ahead.

What Your Thyroid Does During Pregnancy

Your thyroid is a small gland in your neck that produces hormones controlling your metabolism, energy levels, and body temperature. During pregnancy, your thyroid works harder than usual because your baby depends entirely on your thyroid hormones during the first trimester, before their own thyroid gland develops.

These hormones don’t just regulate metabolism. They’re essential for your baby’s brain development, particularly in those critical early weeks. Your body naturally increases thyroid hormone production by about 30 to 50 percent during pregnancy, which is why thyroid problems that weren’t noticeable before can surface once you’re pregnant.

How Common Are Thyroid Problems During Pregnancy?

Thyroid dysfunction affects between 2 and 5 percent of pregnancies when we’re talking about obvious, clinical disease. But milder forms, particularly something called subclinical hypothyroidism, may be present in up to 10 percent of pregnancies, depending on how doctors screen for it.

That means thyroid issues during pregnancy aren’t rare. Many obstetricians now include thyroid function tests as part of routine prenatal bloodwork, especially if you have risk factors like a personal or family history of thyroid disease, Type 1 diabetes, or autoimmune conditions.

What Happens When Your Thyroid Is Underactive During Pregnancy

Hypothyroidism means your thyroid isn’t producing enough hormone. When this condition isn’t treated or is poorly controlled during pregnancy, it can lead to several complications.

For you as the pregnant person, untreated hypothyroidism increases the risk of miscarriage, preeclampsia (dangerously high blood pressure), gestational hypertension, placental abruption (where the placenta separates from the uterus too early), anemia, and postpartum hemorrhage. You might also feel extremely fatigued, have trouble staying warm, gain weight rapidly, or feel mentally foggy, though pregnancy itself can cause some of these symptoms.

For your baby, the risks include preterm birth, low birth weight, and most concerning, impaired brain development. Because thyroid hormones are so crucial for forming neural connections in the first trimester, severe or untreated hypothyroidism during this period can affect your child’s cognitive development and IQ later in life.

The good news is that thyroid hormone replacement with levothyroxine is safe, effective, and usually keeps these risks at bay. Most people with well-controlled hypothyroidism have pregnancy outcomes that look just like those without any thyroid condition.

What Happens When Your Thyroid Is Overactive During Pregnancy

Hyperthyroidism is the opposite problem: your thyroid produces too much hormone. The most common cause during pregnancy is Graves’ disease, an autoimmune condition where your body produces antibodies that stimulate the thyroid.

Uncontrolled hyperthyroidism carries its own set of risks. You might experience miscarriage, preterm delivery, preeclampsia, heart problems including heart failure in severe cases, and low birth weight in your baby. Some people with hyperthyroidism lose weight despite eating normally, have a rapid or irregular heartbeat, feel anxious or shaky, or can’t tolerate heat.

For babies, there’s a particular concern with Graves’ disease because the antibodies causing your overactive thyroid can cross the placenta. This means your baby could develop thyroid problems either before birth or shortly after. Babies can experience fetal growth restriction, thyroid dysfunction after delivery, and in rare cases, stillbirth if the condition goes uncontrolled.

Treatment typically involves antithyroid medications like propylthiouracil or methimazole, which are adjusted carefully because the goal is to use the lowest dose that keeps your thyroid levels in a safe range. Too much medication can cause hypothyroidism in your baby.

The Gray Area of Subclinical Thyroid Dysfunction

Subclinical thyroid dysfunction is trickier. This means your blood tests show mild abnormalities, but you probably don’t have obvious symptoms. Your TSH (thyroid stimulating hormone) might be slightly elevated with normal thyroid hormone levels (subclinical hypothyroidism), or your TSH might be low with normal hormone levels (subclinical hyperthyroidism).

The research on subclinical thyroid problems and pregnancy outcomes is mixed, but some studies suggest increased chances of preeclampsia, gestational hypertension, preterm labor, fetal distress during delivery, gestational diabetes, and subtle neurodevelopmental effects in children.

Whether to treat subclinical thyroid dysfunction during pregnancy is something you and your doctor will decide together, often based on your specific lab values, symptoms, and presence of thyroid antibodies. There isn’t universal agreement in the medical community about treatment thresholds.

Why Thyroid Imbalances Affect Pregnancy So Significantly

Understanding the “why” behind these risks can be helpful. Thyroid hormones don’t just affect one system; they influence nearly every aspect of how pregnancy progresses.

First, they’re directly involved in placental development and function. The placenta is your baby’s life support system, and when thyroid levels are off, the placenta may not work as efficiently at delivering nutrients and oxygen.

Second, thyroid hormones regulate your cardiovascular system’s adaptation to pregnancy. Your blood volume increases by nearly 50 percent during pregnancy, your heart pumps more blood, and your blood vessels dilate. Thyroid imbalances can interfere with these adaptations, contributing to high blood pressure and preeclampsia.

Third, and perhaps most importantly, thyroid hormones directly affect fetal brain development. In the first trimester especially, before your baby’s thyroid gland is functional, their developing brain relies completely on the thyroid hormones you provide through the placenta.

How Doctors Detect and Monitor Thyroid Problems During Pregnancy

If your doctor suspects or wants to screen for thyroid problems, you’ll have a simple blood test measuring TSH and often free T4 (one of the main thyroid hormones).

TSH is usually the first marker that changes when something’s wrong. High TSH suggests hypothyroidism because your pituitary gland is working hard to stimulate an underperforming thyroid. Low TSH suggests hyperthyroidism because your pituitary is backing off in response to too much thyroid hormone.

The tricky part is that normal TSH ranges shift during pregnancy. What’s considered normal when you’re not pregnant might be abnormal during pregnancy, especially in the first trimester. This is why doctors use pregnancy-specific reference ranges.

If you already have a thyroid condition, you’ll likely need blood tests every 4 to 6 weeks during pregnancy, with medication adjustments as needed. People with hypothyroidism often need their levothyroxine dose increased during pregnancy, sometimes by 25 to 50 percent.

Understanding the Real Numbers About Pregnancy Risks

When you read that untreated thyroid disease increases risk, what does that actually mean? Let’s put some context around the numbers.

For preterm birth, untreated thyroid dysfunction increases the odds by about 1.5 to 2.5 times compared to someone without thyroid disease. That sounds significant, but remember the baseline risk of preterm birth is around 10 percent, so even a doubling might bring it to 20 percent. Still a majority chance of carrying to term, though the increased risk is real and worth taking seriously.

For neurodevelopmental outcomes, severe untreated hypothyroidism in early pregnancy can reduce a child’s IQ by several points on average. Mild or well-treated hypothyroidism shows minimal to no effect on cognitive development.

The critical takeaway with all these statistics: outcomes with treated, well-controlled thyroid disease are typically similar to those without any thyroid condition. Treatment makes an enormous difference.

What Treatment Actually Looks Like During Pregnancy

If you have hypothyroidism, treatment is straightforward: a daily levothyroxine pill, usually taken in the morning on an empty stomach. Your dose will be monitored and adjusted throughout pregnancy. Many people who took thyroid medication before pregnancy need an increased dose as soon as they find out they’re pregnant.

For hyperthyroidism, the approach is more complex. You might take propylthiouracil (usually preferred in the first trimester) or methimazole (often used in the second and third trimesters). Your doctor will aim for the lowest effective dose. In some cases, if medication isn’t controlling the hyperthyroidism or is causing problems, thyroid surgery during the second trimester might be considered, though this is uncommon.

Some people with mild hyperthyroidism that’s not from Graves’ disease actually improve during pregnancy without medication, as pregnancy itself can have some immune-modulating effects.

Beyond medication, management includes monitoring your baby’s growth with ultrasounds, watching for signs of preeclampsia or preterm labor, and sometimes checking fetal heart rate if there’s concern about fetal thyroid dysfunction.

What This Means for Your Baby After Birth

If you have Graves’ disease, your baby will need thyroid function tests after delivery because the antibodies that caused your hyperthyroidism can affect your newborn’s thyroid. This neonatal hyperthyroidism is usually temporary, resolving within a few months as your antibodies clear from the baby’s system, but it needs to be monitored and sometimes treated.

Babies born to mothers with well-controlled hypothyroidism typically don’t have thyroid problems themselves and don’t need special testing unless there are other concerns.

All newborns in the United States get screened for congenital hypothyroidism as part of routine newborn screening, regardless of maternal thyroid status.

Moving Forward With Confidence

The relationship between thyroid function and pregnancy is complex, but the essential message is empowering: detection and treatment work. If you had thyroid disease before pregnancy, continuing your treatment and working closely with your healthcare team gives you an excellent chance of a healthy pregnancy. If thyroid problems are discovered during pregnancy, starting treatment promptly protects both you and your baby.

You’re not powerless in this situation. Taking your medication consistently, attending your prenatal appointments, and speaking up about symptoms all matter. The difference between treated and untreated thyroid disease during pregnancy is significant, which means your active participation in your care makes a real difference in outcomes.