It doesn't seem quite fair to accuse your hormones of causing every bloat, blemish and emotional outburst during pregnancy. But the truth is, this potent cocktail of chemicals really is guilty as charged. And much of what’s happening to your body these days — both the good and the not-so-good — can be pinned on them. 

As for the good, did you know that certain hormones are responsible for helping your uterine lining become a soft, safe place for your baby to grow, while others trigger your breasts to produce milk, and others your baby’s bones to form?

But on the less-good side, there are hormones you can blame for pregnancy brain fog (as in, “where are those dang car keys?”) and others that’ll make you cry at the drop of a hat. Pretty crazy stuff from just a few chemicals, right?

For some help sifting through the main hormones that are involved in your pregnancy as well as those that come to the fore after you give birth, here’s a comprehensive guide. Consider yourself armed and ready to learn about the hormones that make your body actually capable of producing a life.

What are the main pregnancy hormones?

Each of the many hormones discussed below has its own job to fill before, during and after pregnancy, but the following are the main ones in pregnancy that get the baby ball rolling, so to speak, and then prepare your body for labor and delivery.[1]

  • FSH (follicle stimulating hormone)
  • LH (luteinizing hormone)
  • hCG (human chorionic gonadotropin)
  • Estrogen 
  • Progesterone
  • Relaxin
  • Placental growth factor
  • HPL (human placental lactogen)
  • Oxytocin
  • Prolactin

Here’s a more in-depth look at each of the main hormones listed above, including the role each plays as well as a few others that have important functions during and after pregnancy.


What is estrogen?

Estrogen is the main female hormone that contributes to sexual development, including the growth of breasts, and it kickstarts and regulates a woman’s menstrual cycle. It also helps to keep your bones healthy and cholesterol levels under control.[2]

What role does estrogen play in pregnancy?

Along with progesterone, estrogen is one of the two main hormones that get the pregnancy party started. Produced by the ovaries and later by the placenta, estrogen helps the uterus grow, maintains uterine lining, regulates other key hormones and triggers the development of baby’s organs. And when it’s time to breastfeed, estrogen promotes the growth of breast tissue and helps milk flow.

Got a stuffy nose — or blotchy skin? Estrogen is also behind swollen mucous membranes and it causes extra blood flow to your skin, which can result in a red, itchy complexion. And estrogen joins other hormones to cause hyperpigmentation like darker nipples and melasma, brown patches on nose, cheeks and forehead.[3]


What is progesterone? 

Progesterone, which is made mostly in the ovaries after each monthly ovulation and helps regulate your menstrual cycle, is the second half, along with estrogen, of the “big two” sex hormones. 

What role does progesterone play in pregnancy? 

This all-important hormone kicks into gear shortly after ovulation by helping the uterine lining to become receptive to implantation of a fertilized egg. Progesterone, along with the hormone relaxin, can cause some GI woes, such as heartburn, indigestion, constipation, and bloating.

Progesterone teams up with relaxin again to help soften ligaments and cartilage, and loosen your joints to prepare you for labor. And if your gums swell and start to bleed, your skin breaks out or you feel super sweaty, that’s the handiwork of this chemical, too.[4]

Follicle stimulating hormone (FSH)

What is FSH? 

The follicle stimulating hormone is made by the pituitary gland in the brain and directs the ovaries to make eggs and estrogen. FSH helps control your monthly cycle.

What role does FSH play in pregnancy?

FSH is the first of a cascade of hormones that’s necessary to launch your pregnancy and is present before you even conceive. FSH stimulates eggs to grow in the ovaries, which increases the production of estrogen. Rising estrogen levels signal the body to produce a surge of LH, leading to ovulation and potentially pregnancy.

Cool fact: women who have fraternal twins tend to have higher levels of FSH, including women over 35, which is why this group is more likely to have double buns in the oven.[5]

Luteinizing hormone (LH)

What is LH? 

Here’s another hormone that’s made by the pituitary gland and works in concert with FSH to orchestrate your menstrual cycle. Luteinizing hormone levels rise just before ovulation and LH triggers the release of an egg from your ovary.

While FSH prompts the production of estrogen, estrogen calls on LH to burst the follicle and free up an egg. The post ovulatory follicle creates the corpus luteum that disintegrates in about 14 days if you are not pregnant, at which point your hormone levels will drop and your period will arrive.[6]

What role does LH play in pregnancy?

If a sperm and egg come together, the corpus luteum lives on, producing the right hormones, including progesterone, to ripen the uterus and nourish your growing baby.

If you’re struggling to conceive, your doctor may check your LH levels. When these are higher than normal, ovulation may be impacted or your hormones may be imbalanced on the whole, which is sometimes behind a case of polycystic ovarian syndrome (PCOS).[7]

Human chorionic gonadotropin (hCG)

What is hCG? 

Human chorionic gonadotropin is a hormone that gets to shine, as it’s normally produced just during pregnancy.[8]

What role does hCG play in pregnancy?

This hormone amps up the production of estrogen and progesterone, though you and hCG may have already met if you’ve taken a home pregnancy test. Yup, it’s this chemical that coaxes a sweet happy face to appear on the pee stick. 

Early on in pregnancy, hCG levels are low, but they soon rise and double every two days, peaking between weeks 7 and 12 and then falling back at the start of your second trimester. Next, the placenta starts making estrogen and progesterone, though hCG is still with you. In fact, this hormone affects the immune system, sometimes leaving you more vulnerable to colds and the flu.


What is prolactin?

Prolactin is another hormone that’s made by the pituitary gland, and if you squint you can see “lact” in this hormone, as in lactating, lactation — and milk![9]

What role does prolactin play in pregnancy?

This milk hormone’s main job is to help enlarge your breasts and produce the milk you’ll need to feed your baby after delivery. Prolactin also charges up the adrenal glands that trigger new hair growth in unexpected places (such as on the belly and face), but this fuzz usually disappears around six months postpartum.

Placenta growth factor

What is placental growth factor? 

You need placental growth factor in order to encourage blood vessel growth which in turn transports the increased blood volume needed to nourish and support a growing baby.

What role does placenta growth factor play in pregnancy?

Not having enough of this pregnancy hormone may cause blood vessels in the placenta to narrow instead of widen, which can cause high blood pressure and possibly preeclampsia. Luckily, medicine is catching up to this problem and new blood and urine tests are helping to measure placental growth factor for early detection and treatment.

Human placental lactogen (hPL)

What is hPL?

Human placental lactogen is also sometimes called human chorionic somatomammotropin, but the “lact” part tells you all you need to know — it’s connected to milk production. 

What role does hPL play in pregnancy?

This hormone is produced by the placenta to adjust your body’s metabolism to feed your baby. Along with placental growth factor, it preps your breasts to breastfeed. This hormone helps make colostrum, which is the antibody-rich pre-milk that precedes actual breastmilk. In some women, hPL and placental growth factor are thought to lead to insulin resistance, resulting in gestational diabetes.


What is relaxin? 

This hormone plays a big role in a woman’s reproductive process. Relaxin levels rise after ovulation and then helps prep the uterine wall to get it ready for pregnancy. Relaxin levels drop back down until the next cycle if there’s no fertilization that month.

What role does relaxin play in pregnancy?

If you do end up conceiving, relaxin is at the ready and lives up to its name, since it helps to relax your muscles, bones, ligaments and joints in the pelvis later in pregnancy in preparation for labor. 

Relaxin also softens and lengthens the cervix. Its limbering mechanism may make you feel off balance and wobbly as you walk (be careful!).[10]


What is oxytocin?

Oxytocin is made by the hypothalamus and then secreted by the all-important pituitary gland. This pregnancy hormone is a critical one when it comes to labor and delivery.

What role does oxytocin play in pregnancy?

Though oxytocin is around throughout your pregnancy, this muscle-contracting hormone is mostly known for stimulating labor contractions. And if your labor is slow to progress, you might get a shot of Pitocin, the synthetic version of oxytocin, to help move things along. Once you’ve delivered, oxytocin helps to shrink the uterus down in size and move milk into the breasts.[11]

Other pregnancy hormones

Did you think that was the end of the list? In fact, there are a few other significant hormones at work during pregnancy, including the following:

  • Erythropoietin: Regulates red blood cell production.
  • Calcitonin: Promotes bone formation.
  • Vasopressin: High levels of this hormone lead to water retention.
  • Thyroxine: A thyroid hormone that increases an expectant mom's oxygen consumption, interacts with growth hormones to regulate and stimulate fetal growth, and is used in the development of the baby's central nervous system.
  • Insulin: Controls the metabolism of foods by both mother and baby.
  • Adrenocorticotropic hormone: A chemical that causes adrenal glands to pump out hormones that contribute to stretch marks and swelling.
  • Cortisol: An adrenal hormone that aids in fetal lung maturation. In high concentrations, cortisol, which is the body’s stress hormone, can interfere with progesterone levels. Cortisol may also adversely affect the hippocampus, which plays a critical role in learning and memory and may explain pregnancy forgetfulness and brain fog.
  • Endorphins: The brain's natural happy hormones can help you endure labor pain — and perhaps forget it altogether once you meet your sweet new baby.

Postpartum hormones

Even after labor and delivery, your body is coursing with hormones. For example, while progesterone and estrogen drop as soon as your infant arrives, oxytocin, sometimes called the “mothering hormone,” sees an uptick. And prolactin is an important post-birth hormone, too, as it encourages the production of breast milk.

The roller coaster that is the mix of postpartum hormones can be tough for some new moms, possibly leading to irritability, tears and the baby blues. These feelings are common, affecting up to 80 percent of new mothers. If you feel sad or out of sorts after the birth of your baby, talk with your doctor.[12]

Some of these pregnancy hormones may seem like alphabet soup at first, but they’re actually a pretty powerful group of chemicals that’s hard at work on your behalf. Have fun getting to know what each of them does and how they affect your body during pregnancy.