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All You Need To Know About Hormones In The First Trimester

From the moment you become pregnant, your hormones go on a roller coaster ride! Here's all you need to know about what is going on in your body and how this may affect how you feel.

Weeks 0 to 13 (the first 3 months) of pregnancy is called the First Trimester, and although you may not be "showing" your pregnancy there is a lot going on in your body. The moment your baby is conceived triggers a dramatic change in your hormone profile and can leave you feeling a little out of kilter.

Common concerns pregnant women experience in the first trimester include:

  • Fatigue

  • Nausea and morning sickness

  • Breast tenderness

  • Softer ligaments in the pelvis

  • Sleep issues

  • Dizzy spells or light-headedness

  • Shortness of breath

  • Frequent urination

  • Indigestion

So let's take a look at how your hormones are changing:

Human Chorionic Gonadotropin (hCG)

Human Chorionic Gonadotropin (or hCG) prevents menstruation and is actually made by the placenta which begins to form at around four weeks. This hormone can be measured in your blood eight days after fertilisation and in your urine 10 days after fertilisation.

At 10 to 12 weeks hCG peaks, and then drops at 16 to 20 weeks. However it will remain above pre-pregnancy levels throughout the rest of your pregnancy.

In early pregnancy hCG will cause your ovaries to release higher amounts of progesterone an estrogens, before the placenta takes over after the first 12 weeks.

Estrogens and Progesterone

Estrogens and Progesterone normally cycle but pregnancy levels of these hormones are much higher, with estrogens increasing to about 30 times the normal levels by the end of your pregnancy.

High levels of estrogens increase the size of your uterus, external genitalia and breast size, it also triggers the growth of breast ducts and relaxes your pelvic ligaments.

Progesterone is important for a successful pregnancy. It helps prevent miscarriage or early delivery by decreasing the contractility of your uterus. It is also involved in the very early development of the foetus and also in the preparation for lactation.

Human Chorionic Somatomammotropin (HCS)

HCS is made by the placenta at around the fifth week of your pregnancy and increases throughout. This hormone alters the your metabolism to ensure that the foetal nutritional needs are met.

HCS stimulates the release of fatty acids from your fat stores, and decreases insulin sensitivity so that you require less glucose and to ensure that more glucose is available for the foetus. Human placental lactogen (hPL) was the original name of HCS, but it doesn't promote lactation in women as it was once thought!


Relaxin is made in your ovaries and is only detectable in pregnant women. This hormone increases in the first trimester and then decreases in the second trimester. It inhibits uterine contractions, relaxes your pubis symphysis and softens your cervix.

Pituitary Hormones

Corticotropin, thyrotropin and prolactin all increase throughout pregnancy, while follicular stimulating hormone (FSH) and luteinizing hormone (LH) decrease. FSH and LH are responsible for stimulating ovary maturation and ovulation, so both these hormones are not needed during pregnancy.

Corticotropin stimulates glucocorticoids.

Thyrotropin stimulates the thyroid to make thyroid hormones triiodythyronine (T3) and thyroxine (T4 which is responsible for increasing metabolic rate).

Adrenocortical Hormones

Glucocorticoids are secreted at slightly higher levels during pregnancy and help with foetal growth and tissue building by allowing the mobilisation of your own body tissues. Glucocorticoids also stimulate the production of glucose from non-carbohydrate sources, decreases glucose use by cells, increase blood glucose concentrations and mobilises the fatty acids. This is so there is more glucose for the foetus, however this also increases your risk of diabetes.

Aldosterone decreases the amount of sodium secreted by the kidneys which tends to lead to water retention. This hormone peaks at the end of pregnancy which leads to the swelling of lower limbs, feet and hands, and occasionally high blood pressure (preeclampsia) during pregnancy.

Thyroid and Parathyroid Hormones

Your thyroid grows by about 50 percent during pregnancy and thyroxine (T4) increases which raises your metabolic rate.

Parathyroid hormone levels also increase due to the growth of the parathyroid. If your diet is low in calcium the parathyroid will grow even larger. Parathyroid hormone regulates blood calcium by increasing the amount of calcium absorbed by the small intestine and releasing calcium absorbed by the small intestine and releasing calcium into your bones.

Parathyroid levels stay high if you breastfeed in order to provide enough calcium for your baby.

As you have discovered in this article, there is a lot going on with your hormone system in the first trimester. So even though you may not be physically showing or announcing your pregnancy at this time, it is important to contact your health care provider as soon as you discover you are pregnant. Take time to connect with your body and aim to use nutrition and exercise to assist with managing your pregnancy symptoms.


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Sophia x

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