The How's and Why's of Pregnancy Hormones

As your body develops to accommodate the growth of your baby, hormones play a role in regulating all the changes. In doing so, your pregnancy hormones—the same ones that cause you to cry at commercials or make your body ache in new ways—are taking to task that your baby makes it to the delivery date safely.

There are six hormones that play a major role in your pregnant months. During this time, these hormones’ levels are also altered. Find out what’s normal and what needs an extra look.

1. Human Chorionic Gonadotropin (hCG) 

HCG is the hormone that announces that a baby is on the way! It signals your body to create the right environment for your baby’s interim home and to stop producing more eggs for reproduction. HCG creates the layer of cells that surround the embryo, and eventually forms the placenta.  

During your 40 weeks of pregnancy, hCG levels tend to fluctuate. They rise rapidly up to your tenth week of gestation, doubling every two days, after which they begin to fall. The high levels of hCG during early pregnancy helps your doctor determine if you have a healthy pregnancy. 

How it affects you: Doctors believe that hCG stimulates an area in the brain that triggers nausea, by making you sensitive to smells and tastes. It’s a possible biological response that has protected mothers and their unborn babies by turning you away from consuming potentially rancid or dangerous food. It may not be the only explanation for morning sickness, but it has been observed that women with higher levels of HCG often experience more nausea and vomiting.

2. Progesterone 

During early pregnancy, your ovaries produce progesterone. It is produced by a cyst called the corpus luteum for the first 10 weeks, after which the placenta is able to make enough progesterone to support the pregnancy and to tolerate having foreign DNA (a new person!) in your body. Progesterone prepares the uterine lining to receive the embryo after ovulation and continues to support the uterine lining during pregnancy, so that the baby has the ideal environment in the womb.

Throughout the pregnancy, progesterone (and another hormone, relaxin) relaxes the normal contractions of the uterus’ smooth muscle, creating room for your baby to have more space as it grows. 

How it affects you: Progesterone, again with relaxin, also relaxes other smooth muscles in your body, which may cause some inconvenience and discomfort, including gastrointestinal issues like indigestion, heartburn, reflux, nausea, constipation, and bloating; while the relaxation of the blood vessels throughout your body can cause lower-than-normal blood pressure and occasionally dizziness. Progesterone is the hormone responsible for the lush hair crowning your head—and possibly the growth of unwanted hair on your breasts and lower abdomen. 

3. Estrogen 

Like progesterone, the corpus luteum secretes estrogen during pregnancy, up until the placenta takes over its production.

Estrogen triggers the development of the fetus, with several organs and other bodily systems, into development. It helps to stimulate hormone production in the fetus's adrenal gland, it stimulates growth of the adrenal gland, and it enhances the mother's uterus, enabling it to respond to oxytocin (another pregnancy hormone; see below).

In early pregnancy, estrogen promotes breast development and later helps it prepare for lactation. As your baby grows in the womb, estrogen triggers the development of little organs and regulates bone density in developing arms and legs. 

How it affects you: Estrogen increases blood flow to mucous membranes, causing them to swell and soften. This usually brings about a stuffy nose, sinus congestion, headaches, and postnasal drip. The extra blood flow also affects the skin, which may manifest as red rashes and blotches, or itchiness in the palms. Having high estrogen levels may also prompt spider veins, nausea, increased appetite. It can also trigger skin changes like hyperpigmentation (darkening of nipples, areola, and white line that runs down your abdomen) and chloasma (or “mask of pregnancy,” darkening of the skin on your forehead, nose, and cheeks). On the plus side, estrogen is behind that gorgeous “pregnancy glow!”

4. Oxytocin

At the beginning of your pregnancy, your oxytocin levels immediately start to rise. It alters your metabolism to create an energy store for your baby, who will need the calories as it grows quickly in the womb.

Known as the love hormone, oxytocin drives the desire to bond, particularly with a parent, child or lover. It’s a biological device to help you build the support system you need to help you when you give birth by making you more open in relationships and happy to get help.

In late pregnancy, it triggers your cautious side so you can make sensible choices to keep you and your growing baby safe. Towards the end of your pregnancy, it's your uterus that becomes very sensitive and responsive to oxytocin. It will stretch the cervix and stimulate the nipples to produce milk

How it affects you: Oxytocin may be the cause of your initial weight gain as your body prepares to feed your baby. It is a crucial component in your pregnancy as it enhances intimacy between you and your loved ones and boosts relationships (which will later increase your need to bond with your baby and your partner). Many believe that oxytocin is needed to help labor progress (while stress inhibits oxytocin and stalls labor!).

5. Prolactin

Prolactin is produced in the pituitary gland in the brain and is known as lactogenic hormone. During pregnancy, prolactin production increases to stimulate the growth of breasts to prepare to produce milk—but until the baby is born, high levels of estrogen and progesterone will halt the milk production. After delivery, estrogen and progesterone levels drop abruptly to induce lactation.

How it affects you: In preparation for lactation, prolactin causes the breast tissue, including milk ducts, areola and nipples, to increase in size.

6. Relaxin

During pregnancy women have 10 times the normal amount relaxin in their bodies. Relaxin loosens up the ligaments that hold the pelvic bones together and relaxes the uterine muscle, getting your body ready to deliver your baby through the birth canal.

During the first trimester, relaxin levels are at their highest to help ensure implantation of the fetus and the growth of the placenta. Early in pregnancy, relaxin helps to inhibit contractions in the wall of the uterus and prevent premature childbirth. 

Relaxin helps your body adapt to the increase in demand for oxygen and nutrients and to process waste products, by regulating the cardiovascular and renal systems.  

How it affects you: Relaxin is responsible for the loosened feeling in your shoulders, knees, hips, and ankles. Because of your body’s lack of support, you may be feeling aches, pain, inflammation, and even clumsy tendencies.