A Cheat Sheet to Pregnancy Hormones

Pregnancy hormones can cause mood swings, tummy troubles, and loose ligaments. Learn about six key hormones, including progesterone and hCG, and their role in pregnancy.

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Pregnancy hormones are amazing and, at times, mysterious things. These powerful chemicals don't just help your body grow a human being; they affect your mind and body, too. They also play a big role in common pregnancy symptoms like morning sickness and heartburn. In short, your changing hormones during pregnancy will impact you (and your fetus) in more ways than one.

But knowledge is power. So, read on to learn about the roles of six key pregnancy hormones, including the symptoms of rising hCG levels, and how they affect you.

Overview of Key Pregnancy Hormones

The following are key pregnancy hormones and their main role in pregnancy:

  • Human chorionic gonadotropin (hCG): Thickens the uterine lining and stops menstruation
  • Progesterone: Prepares the uterus for pregnancy and helps your immune system not reject foreign DNA (the fetus)
  • Estrogen: Aids fetal growth and development, stimulates the rise of oxytocin, and prepares breasts for breastfeeding
  • Relaxin: Loosens ligaments and relaxes arteries
  • Oxytocin: Stimulates uterine contractions
  • Prolactin: Prepares breasts for lactation

HCG

Human chorionic gonadotropin (hCG) is a pregnancy hormone produced by the placenta. Because it's only present during pregnancy, it's sometimes referred to as "the pregnancy hormone." The primary job of hCG is to tell the body that there's life growing in the uterus and that the body needs to build a nest for it. It also tells the ovaries to shut off the production line of maturing and releasing an egg every month.

HCG is necessary for fetal growth and function, placental function, and uterine function. During pregnancy, hCG levels rise eight days after ovulation, peak at 60 to 90 days gestation, and then lower slightly, leveling off for the remainder of the pregnancy. Typically, during the first 10 weeks of pregnancy, hCG levels double every two days.

HCG circulates through the body and is eliminated in the urine (which is what over-the-counter pregnancy tests are looking for). A high concentration of beta hCG in the urine indicates you are pregnant. HCG can also be detected and measured through blood tests.

You can also thank hCG for many early pregnancy symptoms. According to Michele Hakakha, MD, an obstetrician and co-author of Expecting 411, symptoms of rising hCG levels can include:

No one is entirely sure what causes morning sickness, but there is some evidence that high hCG levels are associated with more nausea and vomiting during pregnancy.

Progesterone

In the first trimester, progesterone levels rise exponentially, and then they plateau. Progesterone does some critical jobs along the way, including:

  • Preparing the lining of the womb for implantation
  • Helping the endometrium (uterine lining) secrete nutrients for the embryo
  • Keeping the uterus muscle relaxed
  • Helping your body's immune system tolerate foreign DNA (aka the fetus)

In the luteal phase of the menstrual cycle and early pregnancy, progesterone is produced by a cyst on the ovary called the corpus luteum. It suppresses the maternal immune system, enabling the embryo to survive. The corpus luteum continues to produce progesterone until about 10 weeks, when the placenta takes over its production.

Progesterone relaxes all smooth muscle in the body (most importantly, the muscle wall of the uterus). It also leads to relaxation of the blood vessels throughout the body. These functions can lead to symptoms like:

  • Lower-than-normal blood pressure
  • Dizziness
  • Heartburn or reflux
  • Belching
  • Nausea or vomiting
  • Gas
  • Constipation

Progesterone can also increase hair growth and oil production. As a result, you may notice hair on your breasts and lower abdomen and acne.

Estrogen

Once you've reached the end of the first trimester, your body has higher levels of circulating estrogen, and then the levels plateau.

Like progesterone, estrogen is secreted by the corpus luteum until the placenta takes over. This pregnancy hormone plays a crucial role in fetal development and triggers the growth of several organs and other bodily systems.

The role of this pregnancy hormone is super-important. It helps with:

  • Stimulating the growth of the fetus's adrenal gland
  • Stimulating oxytocin (another pregnancy hormone) to rise in response to increasing levels of estrogen
  • Preparing your breasts for milk production by enlarging the milk ducts

Dr. Hakakha says elevated estrogen levels may also prompt:

  • Spider veins
  • Nausea
  • Increased appetite
  • Skin changes

That said, some are lucky enough to experience the upside of a "pregnancy glow," which is primarily attributed to estrogen levels.

Relaxin

Relaxin is highest in early pregnancy, peaking at the end of the first trimester. It then tapers off and remains low for the rest of the pregnancy.

Relaxin is believed to be responsible for loosening the ligaments that hold the pelvic bones together and relaxing the uterine muscle. These changes prepare your body for the baby's passage through the birth canal.

This pregnancy hormone also relaxes the arteries so they can handle the increased blood volume that accompanies pregnancy without sending your blood pressure through the roof.

You may feel your ligaments are "looser," including your shoulders, knees, hips, and ankles. These looser joints can result in aches, pain, inflammation, and even clumsy tendencies.

Oxytocin

Oxytocin is responsible for stimulating uterine contractions during labor. (Pitocin, a drug commonly given to induce or aid labor, is the synthetic form of oxytocin.)

Oxytocin levels double during the beginning of labor, increasing even more until the second stage of labor. When pressure on the cervix during this stage reaches its peak, oxytocin levels are three to four times higher than at the beginning of labor.

After birth, oxytocin helps your uterus contract to return to its usual size. These contractions are achieved best through nipple stimulation, which is one of the many reasons birth professionals recommend breastfeeding immediately after birth. Oxytocin also promotes milk letdown during lactation and is known as the "cuddle" hormone which promotes bonding with the baby.

In the days and weeks immediately before delivery, some pregnant people experience mild euphoria and strong nesting behavior (inexplicably washing walls, baking, and so on). This behavior may be linked to oxytocin as well as to other hormones and steroids.

Prolactin

Prolactin levels increase 10 to 20 times during pregnancy. For example, a normal level is less than 25 nanograms per milliliter (ng/mL) for someone who is not pregnant. A normal range during pregnancy, on the other hand, is upwards of 80 to 400 ng/mL.

This milk-producing hormone has a tranquilizing effect. Prolactin prepares breast tissues for lactation and the release of milk.

High levels of prolactin can also cause other effects on the body, including:

  • Low libido
  • Milk production
  • Hot flashes
  • Vaginal dryness
  • Breast tenderness

So, if you notice these symptoms during pregnancy or postpartum, it may just be the prolactin at work.

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