Impact of Hypo and Hyper Thyroid Pregnant Mother on the Baby by Dr Lathiesh Kumar Kambham

5 min read

Written by Dr Lathiesh Kumar Kambham

Dr Lathiesh Kumar Kambham

Impact of Hypo and Hyper Thyroid Pregnant Mother on the Baby

Gaining weight during pregnancy is nothing new. Every woman gains a little weight to support the growing fetus. What if the weight gain or loss is not just because of pregnancy but due to your thyroid levels? Did you know pregnancy-related hormonal changes can affect your thyroid hormones too? In this article, we will discuss the effects and impact of hypo and hyper thyroid pregnant mother on their baby.

Thyroid production can be higher or lower than what the body requires, leading to hyper or hypothyroidism respectively. It is a known fact that the expecting mother’s health will have a big impact on the baby growing inside her. It is important to understand to what extent these hormonal fluctuations can affect the fetus.

In This Article

What is Hyperthyroidism?

Hyperthyroidism is a condition where the thyroid gland produces excess thyroid hormone – thyroxine. Excess thyroxine production can speed up the body’s metabolism, thus resulting in burning more calories and losing weight quickly unintentionally. It can cause rapid or irregular heartbeat, both of which require immediate medical attention.

Today, with the advancement of science, there are many medications that can help bring this hyperthyroidism under control. However, when it comes to a pregnant woman, the choices may reduce. Your doctor might not prescribe just any thyroid medicine. They will prescribe a medicine that is both effective and safe during pregnancy.

How Does Hyperthyroidism Affect Fetus?

There is a reason why pregnant women have to watch their health and food intake very carefully. What they eat or what they go through health wise will have an impact on the growing baby’s health. If the mother suffers from hyperthyroidism, it can have the following effects on the fetus:

  • Increase in or fast heartbeat
  • Low weight since the metabolism is overactive
  • Increase in blood pressure
  • Heart failure

What is Hypothyroidism?

When the body makes lesser thyroid than what it requires to carry out all the functions, it is called hypothyroidism. The thyroid gland is underactive, and you may need medications to make up for your body’s requirements.

During pregnancy, if your body is unable to make a sufficient amount of thyroxine to support both your and your growing baby’s needs, it can lead to complications like miscarriage, pre-eclampsia, preterm delivery, or even postpartum hemorrhage.

[Read : What is Premature Delivery]

How Does Hypothyroidism Affect the Fetus?

Just like the way high levels of thyroid affect the baby in a few ways, low levels of thyroid can too. During pregnancy, the mother’s body needs to produce more thyroid than usual, to support the growth of the fetus. If the fetus does not receive enough thyroxine, it can lead to high birth weight, premature birth, respiratory distress in the neonatal stage, and even affect brain development.

Are There Any Side Effects of Thyroid Medication on Baby During Pregnancy?

Any Side Effects of Thyroid Medication on Baby During Pregnancy

During pregnancy, a woman has to be very careful about the medications she takes. The doctor will prescribe only those medicines that are not just effective but are safe for the fetus as well. The medicines she consumes can cross the placenta barrier and reach the baby inside.

When it comes to the thyroid, the pregnant mother’s thyroxine levels must be within safe ranges. If the doctor prescribes thyroid medications, ensure you don’t skip or miss them. The risk related to the medicines is much lower than the risks associated with both hyper and hypothyroidism.

The answer is yes, thyroid medications can affect the fetus but not taking those medicines will have a greater impact, which can start right from birth and last for life. If you have a thyroid issue, it is important to talk to your doctor about it. They will give you the smallest dose possible and not overexpose you or the baby to the medication.

The doctors will consider two factors

  1. The effect of the medicine itself on the fetus
  2. The effect of the medicine on the fetus’ thyroid levels

Sounds confusing? Let’s elaborate –

The medicine you take will mix in your blood and cross the placental barrier and reach the baby. So, overexposure to the medicine can affect the baby which may result in side effects such as birth defects in some cases.

Now, the medicine will act on thyroid levels as such. So, if you are taking medicines for hyperthyroid, it can not only reduce your thyroxine levels, but your baby’s too. This may cause hypothyroidism in the baby if not monitored closely. Similarly, if you are taking medicines for hypothyroidism, remember in addition to the thyroid hormones you and the medicines supply to the fetus, their own body makes some too. Together, it can result in too much of thyroid hormones in the baby.

This is why it is important to consult a qualified doctor and keep a constant check on your thyroid levels, baby’s weight, size, and development of body parts. In most cases, once your thyroid levels reach the safe range, the doctor will discontinue the medication. If needed they may resume again.

Results of some studies don’t recommend certain medicines in the third trimester of pregnancy. So, if your doctor asks you to continue your medicines, ensure you check with them about the safety of the same in different trimesters.

Are There Any Impact of Hypo and Hyper Thyroid Pregnant Mother to the Baby After Birth?

If you don’t address the thyroid fluctuations in time, it can impact the unborn child. While some effects can be short-term or rectifiable like low birth weight or preterm delivery, certain effects are irrecoverable. This is why it is very important to monitor the pregnant mother’s thyroid levels throughout her pregnancy.

If she suffers from hyperthyroidism or graves disease before pregnancy itself, there are chances of transferring the same to the baby. If she develops a thyroid issue during pregnancy, a doctor can control and reduce the risks to the baby to a great extent by monitoring and keeping the thyroxine levels under control.

What Birth Defects Are Caused by Hyperthyroidism and Hypothyroidism?

Birth Defects Are Caused by Hyperthyroidism and Hypothyroidism?

Some of the birth defects caused by hyperthyroidism in pregnancy are:

Some of the birth defects caused by hypothyroidism in pregnancy are:

  • Overweight or underweight babies
  • Low IQ / intellectual disabilities
  • Delay in brain development which can affect motor skills and other important developmental skills
  • Dwarfism

Gestational hyper or hypo-thyroid is not unheard of. Many women experience a fluctuation in their thyroid levels during their pregnancy, which can settle once the baby is born. Both hyper and hypothyroid can be managed with the right medications, close monitoring, and a few lifestyle changes. Trying to avoid the medications to protect the fetus can in fact cause more harm.

[Read : Top 5 Risks With Hypothyroidism In Pregnancy]


1. Can Thyroid Transfer From Mother to Baby?

Yes, the thyroid hormone transfers from the mother to the fetus through the umbilical cord. In the second and third trimesters, the baby’s body will start making its own thyroxine in addition to what it is getting from the mother.

2. Can Thyroid Medicine Cause Birth Defects?

Yes, it can cause certain birth defects. However, if you find a qualified doctor to adjust and monitor your dosages to ensure the thyroid levels are kept in check without affecting the baby with the medications, the birth defects can be very minimal. It does not mean all babies born to mothers who took thyroid medicines will have birth defects. Many women give birth to perfectly healthy babies, despite the medications.

Read Also: Hypothyroidism And Pregnancy- Symptoms, Diagnosis And Treatment

Dr Lathiesh Kumar Kambham,MBBS, MD (Pediatrics)
DM (Neonatology), Lead Neonatology and NICU Services
Aster Women & Children's Hospital
17 years of experience

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