Thyroid Health During Pregnancy: A Comprehensive Guide to TSH, T3, and T4 Levels

Your thyroid hormone levels go up during pregnancy as your body adapts to the changing needs of your body as well as the baby. In the first three months of pregnancy, your baby relies completely on the thyroid hormone secreted by your body to help your baby's brain and nervous system develop properly. Thus, it is vital for your and your baby's health that your thyroid is in good shape during pregnancy.

Now, let's explore why having a normal thyroid level in females during pregnancy is so important

The Role of Thyroid Hormones

The thyroid-stimulating hormone (TSH) released by the pituitary gland stimulates the production of hormones by your thyroid gland, thyroxine (T4) and triiodothyronine (T3), which impact your heart rate, metabolism, and many other body functions. T4 is more abundant and is converted into T3 by certain organs in your body for effective utilisation.

T3 and T4 affect every cell and organ in your body by:

• Adjusting the speed of your heartbeat
• Managing how fast your body uses energy
• Changing your body temperature
• Impacting your digestive ability
• Playing a role in brain development
• Overseeing the health of your skin and bones by regulating how quickly your body replaces old cells (a natural process)
• Controlling the contraction of your muscles

At times, the thyroid gland may produce an excess or insufficient amount of these hormones. When this occurs, it results in a thyroid disorder. Maintaining proper thyroid function throughout pregnancy is crucial for the well-being of both the mother and the developing foetus, as it supports the proper development of your baby's brain and nervous system.

Normal Thyroid Levels in Pregnancy

Let us discuss normal T3, T4, TSH levels during pregnancy.

Normal TSH levels in pregnancy are as follows:

• First trimester: 0.129-3.120 uIU/mL
• Second trimester: 0.274-2.652 uIU/mL
• Third trimester: 0.312-2.947 uIU/mL

The normal ranges for T3 and T4 (pmol/L) during pregnancy are 3.8 to 5.3 and 12.1 to 15.7, respectively. Further details for each trimester and the significance of normal TSH values will be provided in the upcoming sections

Monitoring Thyroid Levels During Pregnancy

Pregnancy causes alterations in thyroid hormone levels, which may not be associated with any symptoms. However, a few individuals might face serious thyroid issues during pregnancy. About 2 to 3 out of every 100 pregnancies are affected by thyroid dysfunction. Therefore, it's crucial to assess thyroid levels as a component of prenatal care.

It's usual for TSH levels to be slightly lower than normal in the first trimester, followed by a gradual rise. Your doctor will conduct a general physical examination and advise blood tests to assess your thyroid levels throughout the pregnancy to determine if you need medication to prevent any untoward complications for you or your child.

TSH Level in Pregnancy

It’s important that your TSH levels be in the normal range throughout the pregnancy. Altered TSH levels can pose potential problems for the mother as well as the developing baby. Let's learn about the causes of high TSH levels and their possible complications.

A high TSH in pregnancy could indicate that your thyroid isn't producing sufficient thyroid hormone due to an underactive thyroid (hypothyroidism). It might happen because of:

• Inadequate iodine levels in the body
• An immune disorder you already have
• Past illness of the thyroid gland1
• Hashimoto's disease

Untreated hypothyroidism during pregnancy can lead to the following complications in expecting mothers:

• Anaemia
• Hypertension
• Heart failure
• Pre-eclampsia (a condition where organs like the kidneys and liver don’t function properly due to hypertension)
• Placental abruption (separation of the placenta from uterus before birth)
• Postpartum haemorrhage (heavy bleeding after delivery)
• Myxoedema (a condition of severe hypothyroidism that can be fatal)

For babies, the risks of untreated hypothyroidism encompass:

• Infantile myxoedema
• Low birth weight
• Impairment of growth, such as brain development and nervous system function
• Stillbirth or miscarriage
• Thyroid problem

Low TSH in pregnancy indicates that your thyroid gland is producing thyroid hormones in excess (hyperthyroidism). This is often caused by the thyroid gland being overly active due to conditions such as:

• Graves' disease or
• Thyroid nodules

For expecting mothers, this can lead to complications such as:

• Pre-eclampsia
• Pulmonary hypertension
• Placental abruption
• Heart failure
• Thyroid storm

For babies, the risks involve:

• Premature birth
• Low birth weight
• Goitre
• Impaired thyroid function
• Stillbirth or miscarriage

Therefore, to ensure the well-being of both you and your baby, it's crucial to keep thyroid levels in check.

T3 and T4 Levels During Pregnancy

T3 levels during pregnancy are as follows:

• First trimester: 3.8 to 6.3 pmol/L
• Second trimester: 3.5 to 6.1 pmol/L
• Third trimester: 3.4 to 5.3 pmol/L

T4 levels during pregnancy are as follows:

• First trimester: 12.1 to 18.7 pmol/L
• Second trimester: 9.1 to 18.3 pmol/L
• Third trimester: 8.4 to 15.7 pmol/L

Values above and below this range are considered as hyper- and hypothyroidism, respectively. Untreated thyroid conditions may lead to complications for both you and your baby, as described earlier.

Thyroid hormones help in the baby's brain development before birth by influencing the formation of brain cells, their movement, and branching, and the formation of protective covering around these cells. Thyroid hormone deficiency can affect the brain growth before and after birth, causing neurological impairment, intellectual deficits, and retarded growth.

In case of altered thyroid levels, your doctor will suggest tailored treatment based on your circumstances.

Free T4 Range in Pregnancy

Detecting hypothyroidism and hyperthyroidism during the early stages of pregnancy is vital for the well-being of both you and your baby. For this, the most commonly followed recommendation is to test for the levels of free T4 and TSH in the blood as they are considered better markers for thyroid problems in some cases.

The free T4 trimester-specific reference ranges are 0.8 to 1.53 ng/dL for the first trimester, 0.7 to 1.20 ng/dL for the second trimester, and 0.7 to 1.20 ng/dL for the third trimester.

Maintaining thyroid levels in pregnancy is essential for a successful pregnancy and the well-being of both mother and baby. Regular monitoring and proper medical guidance are keys to preventing potential complications of thyroid issues. Therefore, Orange Health Labs brings to you the best pregnancy test packages with the quickest and most accurate results at your doorstep to ensure a happy and safe pregnancy.