Low T4 Levels During Pregnancy: Impacts on Thyroid Health and Fetal Development

At 12 weeks of pregnancy, the T3 levels are normal, but the T4 levels are very low (0.4)?

Hello Doctor, prior to the IVF procedure, I had a thyroid function test which showed normal values, but I tested positive for Anti-TPO.
I started taking half a tablet of Antithyroid medication daily from the third day of my menstrual cycle until I reached 12 weeks of pregnancy, at which point the doctor advised me to stop taking it and to check T3 and T4 levels.
During my 16-week prenatal checkup, the test results showed normal T3 levels but very low T4 levels.
I am currently waiting for the thyroid report from the endocrinology department.
What do these values indicate? Is this hypothyroidism? Could it affect the fetus? I have heard it can impact the baby's intelligence.
Will stopping the medication this month have any effects on the baby?

Lin, 30~39 year old female. Ask Date: 2019/05/03

Dr. Hong Yuanbin reply Internal Medicine

Hello, the commonly used indices for thyroid function tests are TSH, T3, and T4, with T4 preferably measured as free T4.
If TSH is very high and both T3 and free T4 are low, it indicates hypothyroidism.
However, your values seem to be one normal and one low, which may not necessarily indicate true hypothyroidism.
A comprehensive assessment, including other test results and clinical symptoms, is needed to evaluate your actual condition.
Regarding the impact on the fetus, a holistic evaluation is also required to determine the effects.
It is recommended to continue monitoring and assessment at a metabolic clinic.
Thank you for your inquiry.

Reply Date: 2019/05/03

More Info

Low thyroid hormone levels during pregnancy, particularly low Free T4 levels, can have significant implications for both maternal health and fetal development. Thyroid hormones are crucial for various physiological processes, including metabolism, growth, and development. In pregnant women, these hormones play an essential role in the development of the fetal brain and nervous system.

When a pregnant woman has low T4 levels, it can indicate hypothyroidism, which is a condition where the thyroid gland does not produce enough thyroid hormones. The normal range for Free T4 during pregnancy is generally higher than in non-pregnant individuals due to the increased demand for thyroid hormones to support both the mother and the developing fetus. The American Thyroid Association recommends that TSH levels should ideally be below 2.5 mIU/L in the first trimester and below 3.0 mIU/L in the second and third trimesters to minimize risks to the fetus.

In your case, with a normal T3 level and a low T4 level, it is essential to consider the overall clinical picture. The presence of anti-TPO antibodies suggests that there may be an autoimmune component to your thyroid function, which can complicate the situation. While low T4 levels can potentially affect fetal brain development and may be associated with lower IQ in children, the extent of this impact can vary based on the timing and severity of the hypothyroidism.

Regarding your concern about the month without medication, it is difficult to quantify the exact impact on the fetus without further assessment. However, the critical period for fetal brain development occurs in the first trimester, and any thyroid hormone deficiency during this time can have lasting effects. If you have been diagnosed with hypothyroidism, it is crucial to resume treatment as soon as possible to restore normal hormone levels.

It is advisable to follow up with an endocrinologist or a healthcare provider specializing in maternal-fetal medicine. They can provide a comprehensive evaluation of your thyroid function and recommend appropriate treatment. Regular monitoring of thyroid hormone levels throughout your pregnancy is essential to ensure that both you and your baby remain healthy.

In summary, low T4 levels during pregnancy can pose risks to fetal development, particularly concerning brain development and cognitive function. It is vital to address any thyroid hormone deficiencies promptly and to maintain regular follow-up appointments to monitor thyroid function throughout your pregnancy. If you have any further concerns or questions, do not hesitate to seek additional medical advice.

Similar Q&A

Thyroid Health During Pregnancy: Impacts of T4 Levels and Past Conditions

I am 4 months pregnant and had a blood test for thyroid hormones T4 and TSH. The results were T4 = 16.4 (normal range = 4.2–12.5), and TSH was within the normal range. I have a history of pheochromocytoma and am concerned about any potential effects on the fetus and myself.

Dr. Wang Hanzhou reply Obstetrics and Gynecology
During pregnancy, thyroid function may slightly increase (T4 level at 16.4). It is advisable to consult a specialist in thyroid disorders.

Understanding Hypothyroidism in Late Pregnancy: Key Concerns and Questions

Hello Doctor: I am currently 29 weeks and 2 days pregnant. On May 19, I went to Hospital A to check my thyroid function (I had no discomfort, I just wanted to understand my condition). On June 2, I received the following results: Free T4: 0.79 (normal range 0.89-1.76), TSH: 3.55 ...

Dr. Zhang Kunmin reply Obstetrics and Gynecology
Hello, 1. If hypothyroidism is diagnosed during pregnancy, it is essential to restore thyroid function to normal as quickly as possible. Adjust the T4 dosage to achieve and maintain serum thyroid-stimulating hormone (TSH) levels (using international standard measurement methods...

Understanding Chronic Thyroiditis: Impact on Fertility and Pregnancy

Hello, doctor. Last May, I had a blood test that revealed my thyroid antibody level (TA) was 800, while other indices (TSH, T3, T4, MA) were normal. After taking quinine for a year, my TA level decreased to 470, but the other indices remain normal. My husband and I want to have a...

Dr. Zeng Guosen reply Internal Medicine
Dear Ms. Hsueh, I apologize for the delayed response as I have just returned to the country. Elevated thyroid antibodies with normal thyroid function (paying attention to TSH and Free T4) and the absence of symptoms should not pose a risk for miscarriage. I recommend seeking a ...

Low TSH Levels at 13 Weeks Pregnant: Implications for Fetal Health

Hello Doctor: I am a pregnant woman at 13 weeks and 3 days, and I would like to ask you about thyroid hormones. I had my thyroid function tested at 13 weeks and 1 day, and the results were: TSH: 0.05 uIU/ml, FREE-T4: 0.99 ng/dl. Is the low TSH level concerning for the fetus? Do I...

Dr. Yuan Tianmin reply Breast and Thyroid
Your obstetrician-gynecologist should have explained the report to you. If you still have any unclear areas, you can visit the endocrinology department for further consultation.