The Hormones of Pregnancy

If you've ever blamed "pregnancy hormones" for tears at a commercial or a sudden wave of exhaustion, you're not wrong. Hormones guide almost everything that happens during pregnancy, from keeping your pregnancy going in the earliest weeks to starting labor and making milk.

They also explain many of the symptoms you feel along the way, like nausea, heartburn, looser joints and mood changes. Knowing what's happening in your body can make those changes feel less mysterious, and help you recognize when something deserves a call to your provider.

Pregnancy hormones at a glance

• hCG: tells your body you're pregnant and keeps progesterone flowing early on
• Progesterone: keeps the uterine lining in place and the uterus relaxed
• Estrogen: boosts blood flow and helps your uterus, placenta and breasts grow
• Relaxin: helps your blood vessels and uterus adjust to pregnancy
• hPL: shifts your metabolism so more sugar reaches your baby
• Prolactin: prepares your breasts to make milk
• Oxytocin: powers contractions, limits bleeding after birth and triggers milk let-down
• Endorphins: your body's natural pain relief during labor

The hormones that keep pregnancy going

hCG: the pregnancy test hormone

Human chorionic gonadotropin (hCG) is made by the developing placenta soon after a fertilized egg implants in your uterus. It tells your body you're pregnant and keeps progesterone flowing in the early weeks. It's also what a pregnancy test detects.

hCG rises quickly in early pregnancy, peaks around 8 to 11 weeks, then falls and levels off for the rest of pregnancy.

You might notice: Nausea and morning sickness are often worst when hCG is highest. For many people, they ease in the second trimester as hCG levels off.

When to call: Let your provider know if you can't keep food or fluids down, you're losing weight, or you feel dizzy or faint. Severe, ongoing vomiting can be a condition called hyperemesis gravidarum, which is treatable.

Progesterone: the pregnancy keeper

At first, progesterone comes from your ovaries. Over the first trimester, the placenta takes over. Progesterone keeps the lining of your uterus in place and helps keep the uterus relaxed so it doesn't contract too early. Levels keep rising throughout pregnancy.

You might notice: Progesterone relaxes smooth muscle throughout your body, not just in your uterus. That can slow digestion and loosen the valve at the top of your stomach, leading to constipation, bloating and heartburn. It can also make you feel more tired, especially in the first trimester.

Estrogen: the builder

During pregnancy, most estrogen comes from the placenta. It increases blood flow, helps your uterus and placenta grow, and develops the milk ducts in your breasts. Like progesterone, estrogen rises steadily until birth.

You might notice: Extra blood flow and estrogen can cause a stuffy nose, nosebleeds, breast changes, darker patches of skin on your face, and the flushed skin some people call the pregnancy "glow."

Relaxin: the loosener

Relaxin is made by your ovaries and the placenta. It's highest in the first trimester, when it helps relax your blood vessels and uterus as your body adjusts to pregnancy. It may also help loosen ligaments and soften the cervix, but researchers are still learning how much relaxin affects your joints.

You might notice: Looser joints, hip or pelvic discomfort, or feeling a little off balance as your body changes. If pelvic pain makes it hard to walk, climb stairs or roll over in bed, ask your provider whether physical therapy could help.

The hormones that prepare for baby and birth

hPL: the fuel manager

Human placental lactogen (hPL) is made by the placenta. It shifts your metabolism so more glucose, or sugar, reaches your baby. It does this partly by making your body more resistant to insulin. hPL rises through pregnancy and is highest in the third trimester.

You might notice: You won't feel hPL directly, but it's one reason you're screened for gestational diabetes between 24 and 28 weeks. Most people's bodies keep up by making more insulin. When yours can't, blood sugar can run high. Gestational diabetes is common and can be managed.

Prolactin: the milk maker

Prolactin is made by the pituitary gland in your brain. It rises steadily from early pregnancy until birth and prepares your breasts to make milk. During pregnancy, high progesterone holds back full milk production. Once the placenta is delivered and progesterone drops, prolactin can do its full job.

You might notice: Fuller, heavier breasts, and sometimes a little colostrum, your first milk, leaking in the second or third trimester. Leaking or not leaking doesn't predict how much milk you'll make.

Oxytocin: the labor and love hormone

Oxytocin is made in your brain and released by the pituitary gland. Levels rise during labor and help power your contractions. After birth, oxytocin helps your uterus contract to limit bleeding, triggers the milk let-down reflex, and supports bonding with your baby. Skin-to-skin contact after birth can help boost it.

You may hear about Pitocin, a synthetic form of oxytocin. It can be used to start labor, strengthen contractions, or prevent and treat heavy bleeding after birth.

You might notice: Contractions during labor, and cramping, called afterpains, while breastfeeding in the first days after birth.

Endorphins: your natural pain relief

Endorphins are made in your brain and rise during labor. They help your body cope with pain and stress.

You might notice: A focused, "in the zone" feeling during labor. Feeling calm, safe and supported may help your body do this work.

After birth: the big hormone drop

Once the placenta is delivered, estrogen and progesterone fall quickly. At the same time, prolactin and oxytocin take the lead as your body begins making milk and recovering from birth.

This sudden shift, along with little sleep and a big life change, can bring the baby blues. You might feel weepy, moody, irritable or anxious. The baby blues are very common, often start a few days after birth, and usually ease within about two weeks.

Sometimes those feelings don't pass, or they become more intense. That can be a sign of postpartum depression or anxiety, which are common and treatable. They can start any time in the first year after birth, and partners can experience them too.

The BirthX takeaway

Your hormones are working hard from the first weeks of pregnancy through birth and beyond. Many of the symptoms you feel, from morning sickness to heartburn to the baby blues, have a clear reason behind them.

Knowing what's happening in your body can help you feel more prepared, ask better questions and recognize when something isn't typical. Download the one-page summary to keep on hand. If something doesn't feel right, physically or emotionally, you deserve to be heard, so reach out to your provider.

This article is for education only and is not a substitute for medical advice. Always contact your provider with concerns.

Sources: Cleveland Clinic, Human chorionic gonadotropin (hCG); Cleveland Clinic, Progesterone; Cleveland Clinic, Relaxin; Cleveland Clinic, Oxytocin; Rassie et al., Human placental lactogen in relation to maternal metabolic health and fetal outcomes, Frontiers in Endocrinology (2022); Rassie et al., Lactogenic hormones in relation to maternal metabolic health in pregnancy and postpartum: protocol for a systematic review, BMJ Open (2022); HRSA, National Maternal Mental Health Hotline.