Hormone Series: Your Hormones During Pregnancy

Welcome to part 2 of our hormone series. Last week we talked about your hormones and how they change throughout your menstrual cycle which you can check out here. Today we are going to talk about what happens if the egg released from your ovaries during a menstrual cycle is fertilized…that’s right, we’re talking pregnancy.

Over the course of your pregnancy your hormone profile will change dramatically and immediately. Initially women will experience dramatic increases in estrogen and progesterone but there are also numerous other hormones that will be impacted throughout pregnancy. These dramatic changes in hormones can impact how you feel (mood as well as physically) and they will likely alter the physical impact of exercise and movement on your body over the course of your pregnancy. All of these changes take place to help the baby grow and develop into a healthy bundle of joy that you will hold in your arms.

Over the course of a single pregnancy women will produce more estrogen than they will throughout the rest of their entire life. This increase in estrogen allows the uterus and placenta to form the blood vessels needed to deliver nutrients and support the baby as they develop and grow. Estrogen levels will increase steadily over the course of the pregnancy reaching their highest levels in the third trimester. It is believed that this sharp increase in estrogen during the first trimester may cause some of the nausea and morning sickness generally associated with the first trimester of pregnancy. During the second trimester estrogen plays a major role in the development of milk ducts.

Progesterone levels also increase dramatically during pregnancy. These high levels of progesterone can cause laxity in ligaments and joints through the body and an increase in the size of internal structures like the ureters (which connect the kidneys to the bladder). Progesterone also plays an important role in allowing the uterus to accommodate a full term sized baby.

So that gives you an overview of what happens to your hormones during pregnancy but let’s take a brief look at what changes happen in each trimester as your pregnancy progresses.

In your first trimester progesterone and estrogen levels rise dramatically but the body also begins producing human chorionic gonadotropin (hCG). Progesterone helps to act as a muscle relaxant which prevents your uterus from contracting until the onset of labour (this can slow down digestion and lead to constipation). Progesterone can also be responsible for some of the mood swings that you may experience in the first trimester. Estrogen is high at this time as well as it helps to regulate progesterone and maintains the endometrial lining (which is vital for the baby’s development). The increase in blood flow that is caused by estrogen can make your breasts achy and tender as well as cause a stuffy nose (due to swelling of mucous membranes in the nasal passages) and can increase your frequency of urination (kidneys process extra fluids and your uterus puts pressure on your bladder). hCG is only produced during pregnancy and is the hormone that indicates the formation fo the placenta. hCG can also cause you to feel nauseous as well. In the first trimester you will experience an increase in thyroid hormones to help support the baby’s neurodevelopment and bone development. Increases in hCG and estrogen cause these increases in the thyroid hormones to help ensure both you and the baby are getting enough thyroid hormone.

Generally as women enter the second trimester they start to feel less nauseous and experience some increased energy levels again. In the second trimester the hormone relaxin begins to increase which cause your muscles and joints to relax and loosen up. This may lead to some aches and pains in ligaments and injuries may occur more easily. Estrogen and progesterone will continue to increase during the second trimester promoting growth of baby. They will also stimulate the melanocyte- stimulating hormones (triggers your skin’s melanocytes to produce melanin which will give your skin colour). This may result in brown or grey patches around the face, a dark line that goes up your belly, nipples, moles and freckles may also darken as well. You may experience increased hair growth at this time as well due to the surges in estrogen. Cortisol levels also increase during pregnancy and are increasing during the second trimester. Cortisol is important because it helps regulate your metabolism and control blood sugar levels. Human placental lactose (HPL) is secreted from the placenta to help baby grow.

By the third trimester the hormones you will need in the postpartum period are starting to be produced by the body. Estrogen and progesterone levels will continue to rise and will be at their highest around 32 weeks. Estrogen may play a role in some of the swelling you notice at this point as it helps synthesize a hormone related to salt and water retention. With high levels of progesterone you may also experience relaxation of the sphincter at the base of the esophagus which can cause heartburn. Relaxin continues to relax the ligaments in preparation for delivery. In the third trimester prolactin also stimulates the development of breast tissue to prepare for lactation in the postpartum period.

As you can see your body goes through a large range of hormonal changes throughout pregnancy. Remember during this time to give yourself grace as some of these hormonal changes will impact your mood and how you physically feel. All these changes take place to help baby grow big and healthy, but there might be days where you don’t feel like that. Be patient with yourself as these changes take place and know that these things aren’t permanent. Join me next week as we talk about hormones during labour and what happens to all those hormones in the postpartum period.