8 Pregnancy Hormones Impacting Your Fertility Journey

by Aug 25, 2021

Getting pregnant doesn’t happen magically. Even if you and your partner are both fertile, you still only have a 25% chance of getting pregnant each cycle. Conception is a dance between your fertility hormones and your partner’s — and if you aren’t paying attention to the data, it could take months or even years to figure out what’s not working.

Hormones control everything in our bodies from our appetites to our moods to our fertility but nowhere do they shine more than during pregnancy.  Pregnancy hormones turn your body into a baby maker and control everything from how the fetus grows to changes in your muscles.

There are eight major pregnancy hormones at play when trying to conceive:

  • Estrogen
  • Progesterone
  • Luteinizing Hormone (LH)
  • Follicle Stimulating Hormone (FSH)
  • Human Chorionic Gonadotropin (hCG)
  • Relaxin
  • Oxytocin
  • Prolactin

Much of what is happening to your body during pregnancy can be pinned on these hormones and in this post we will go over what each hormone is, what it does during pregnancy, and how your hormones change over the course of a successful pregnancy.

Pregnancy Hormones


What is estrogen?

Estrogen is a primary sex hormone found in women’s bodies that helps regulate the menstrual cycle, fertility, and overall health.  Estrogen is produced by the follicles and corpus luteum after ovulation.

Healthy estrogen levels are essential for an ovulatory menstrual cycle and estrogen plays a key role in many functions throughout the body.  It plays a role in bone formation, cholesterol levels, and the development of secondary female sex characteristics like breasts and pubic hair, not to mention cardiovascular functions and mood management.

Estrogen is also responsible for building up the lining of your uterus every month and helps regulate the flow and thickness of uterine mucus secretions. It’s also responsible for the formation of breast tissue and stopping the flow of milk after weaning.

What does estrogen do during pregnancy?

During pregnancy, estrogen helps the uterus grow, aids in fetal development and maintains the uterine lining.  Estrogen also helps regulate other key hormones and increases blood flow, making it responsible for that pregnancy “glow” you might experience.  It also promotes the growth of breast tissue and the flow of milk for breastfeeding.


What is progesterone?

The pregnancy hormone progesterone is essential for fully-functioning fallopian tubes, a healthy period, and ensures you are able to get and stay pregnant until full term.

On top of that, all other female fertility hormones are made from progesterone. That makes it a pretty important hormone to track for your fertility and overall health!

Sometimes called the pregnancy hormone, progesterone works on many fronts. From preparing your body for pregnancy to its role in your libido, progesterone primarily supports your body in getting pregnant and maintaining that pregnancy.

Secreted by the corpus luteum, progesterone is mainly produced in the ovaries. The corpus luteum, a temporary gland formed in the ovaries after ovulation, is made from a follicle that housed a maturing egg and forms as soon as the egg pops out.

A small amount of progesterone is produced by the adrenal glands that sit atop the kidneys, and once pregnant, production takes place in the placenta.


What does progesterone do during pregnancy?

Progesterone primarily supports your body in maintaining a pregnancy.  It does this by thickening the uterine lining to welcome a fertilized egg and maintaining that lining throughout pregnancy.

Progesterone works on the smooth muscles and prevents uterine contractions so the uterus doesn’t reject the fetus.  It also helps prime the glands involved in breastfeeding to get your breasts ready to start making milk.

Luteinizing Hormone (LH)

What is luteinizing hormone?

LH is produced in the anterior pituitary gland and is responsible for triggering ovulation and the development of the corpus luteum in the ovary. During ovulation, LH levels surge and send a signal to the ovary that it’s time to release an egg.  LH works on the follicle to burst and free up the egg for fertilization.

What does LH do during pregnancy?

LH’s main role is in ovulation and it doesn’t play much of a role in pregnancy.  Once the follicle has burst, cells proliferate and it becomes the corpus luteum, producing progesterone.  Early on in pregnancy, your brain shifts from producing hormones that support ovulation to those that maintain pregnancy so LH is no longer needed.  LH levels typically drop and stay low across pregnancy.

Follicle Stimulating Hormone (FSH)

What is follicle stimulating hormone?

As the name suggests, follicle stimulating hormone triggers the ovaries to make eggs and estrogen by stimulating the follicles.  Like LH, FSH is produced by the anterior pituitary gland in the brain and helps control your monthly cycle. They work together to tell follicles in the ovaries to begin maturing. It’s important for your ovaries to release an egg when you ovulate because only eggs can be fertilized.

FSH also affects the levels of estrogen that then has an impact on your cervical mucus, one of the telltale signs you’re within your fertile window. Most of the time, your cervical mucus will be thick, white or off-white, and creamy. When you are ovulating, however, your cervical mucus becomes stretchy and clear, like the consistency of an egg white, to help sperm survive and reach an egg. FSH is responsible for this important change.

What does FSH do during pregnancy?

If an embryo has implanted in the uterine wall, FSH levels begin to drop and stay low for the duration of the pregnancy.  Because your cycle is temporarily paused while pregnant, FSH levels are naturally low during this time.

Human Chorionic Gonadotropin (HcG)

What is human chorionic gonadotropin?

Also known as hCG or beta hCG and released mainly during pregnancy, this is the pregnancy hormone that home pregnancy tests detect and measure in your urine to determine a positive result.  As early pregnancy progresses, hCG levels typically follow a predictable pattern of increasing, but that may not always be the case.

Although it is produced naturally in the body and you may find trace amounts in your system at other times, hCG is really only produced once an embryo implants in the uterus.

What does hCG do during pregnancy?

HCG is produced by the cells surrounding a developing embryo that eventually go on to form the placenta.  Production of this hormone kicks in almost immediately after implantation and levels double every 72 hours during the early weeks of pregnancy.

After implantation happens and hCG starts to be produced, it ensures the corpus luteum continues to produce progesterone throughout the first trimester of pregnancy.  Without progesterone, the womb lining would shed and prevent an embryo from implanting.  hCG makes sure this doesn’t happen by ensuring the corpus luteum continues progesterone production until the placenta is established and can take over production.

In addition to how it triggers progesterone production and supports fetal growth, hCG also supports other bodily functions over the course of a pregnancy. It promotes the development of new blood vessels in the uterus as well as smoothing the muscle cells in the uterine wall, both critical developments for maintaining a pregnancy.  The main function of hCG though is to trigger the corpus luteum to continue progesterone production and prevent the embryo from being rejected due to immunological reasons.


What is relaxin?

Relaxin is the hormone known for its role in facilitating childbirth (although research suggests it may play a role in the development of the endometrium as well).  It is also produced by the corpus luteum after ovulation in order to help promote implantation of the embryo.

This pregnancy hormone is primarily involved in the loosening of ligaments, muscles, and joints to facilitate a growing body and childbirth.  Most importantly, as the fetus grows, it allows the uterus to expand by signaling the uterine ligaments to loosen up.

What does relaxin do during pregnancy?

Levels of this hormone steadily increase as pregnancy progresses.  Relaxin plays a starring role in childbirth as it works on the ligaments and joints to loosen up and creates space for them to expand during birth.  It also works on the cervix by softening and lengthening it in preparation for labor.


What is oxytocin?

Produced by the hypothalamus and secreted by the pituitary gland, this pregnancy hormone plays a crucial role in labor and breastfeeding.  It stimulates the uterine muscles to contract so labor begins and the baby is pushed out.  It also increases relaxation, lowers stress and anxiety, and plays a role in bonding.

What does oxytocin do during pregnancy?

Levels of this hormone gradually increase during pregnancy and then have a sharp increase during labor and delivery.  This makes sense given its role in stimulating contractions but oxytocin also helps move the baby down and out of the birth canal and limits bleeding at the site of the placenta.  After delivery oxytocin helps shrink the uterus in size and aid in milk production.


What is prolactin?

Named for its role in lactation, this hormone promotes breast milk production as well as a variety of other functions in the body.  Prolactin is produced in the pituitary gland as well as the uterus, immune cells, brain, breasts, and fat tissue.  Production is partially controlled by estrogen and it is released in high levels when a newborn baby suckles at their mother’s breast.  Levels rise significantly during pregnancy to prepare your breasts for breastfeeding.

What does prolactin do during pregnancy?

Given its role in breastfeeding, prolactin prepares your breasts to begin milk production.  It helps make breast milk and levels may increase by 10 to 20 times during pregnancy.  During pregnancy, its main job is to help enlarge your breasts and kickstart the milk production you’ll need to feed your baby.

When do pregnancy hormones start?

Hormones are always sending information in our bodies but pregnancy hormones follow a set and predictable schedule during healthy pregnancies.

First trimester

During the first trimester, progesterone, estrogen, and hCG play a starring role.  Because hCG is the hormone that indicates pregnancy, this is often the first pregnancy hormone really at work, and is even responsible for a positive result on a home pregnancy test.  Levels of these hormones rise rapidly during the first trimester and you may begin to experience symptoms you’ve never experienced before.

Second trimester

During the second trimester, you’ll start to see increases in relaxin as your body needs to accommodate a growing uterus and fetus.  You may start to notice new sensations (or pain) in your muscles and joints as relaxin works its magic to loosen your body up for childbirth.  Estrogen and progesterone will continue to rise as progesterone dominates throughout the pregnancy.

Third trimester

Your third trimester will continue to see rising estrogen levels until they peak at around 32 weeks with progesterone.  Prolactin production will increase to get the body ready for lactation and is almost ten times higher at the end of pregnancy than at the beginning.  Oxytocin will significantly increase to prepare for labor and is helpful with feelings of bonding and motherhood after birth.

Many other hormones are involved in pregnancy and each has a role to play.  Even though they may seem all over the place, these pregnancy hormones work together on your behalf over the course of a successful pregnancy.

✔️ Medically Reviewed by Katerina Shkodzik, M.D., OB-GYN

Dr. Katerina Shkodzik is a certified OB-GYN with a special focus on reproductive endocrinology and infertility issues. She has been practising since 2015.

Dr. Shkodzik completed her residency program in the Department of OB/GYN at the Belarusian State Medical University and fellowship program in the Department of Gynecological Surgery at the Medical University of Bialystok, Poland.

Dr. Shkodzik is extensively involved in digital health projects providing her medical expertise and integrating of cutting edge technologies in medical science and clinical practice since 2018.

Dr. Shkodzik has participated in several studies focused on PCOS, endometriosis, menstrual cycle characteristics and their abnormalities based on big data of digital health in collaboration with leading universities.

She believes that paying special attention to women's health is a crucial step to improving the world we live in.

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