A Cheat Sheet to Pregnancy Hormones

From emotions that change on a dime to tummy troubles and loose ligaments, your hormones during pregnancy can take you for quite a ride. Here, we explain what's going on with six key hormones, including progesterone, HCG, and oxytocin.

pregnant woman holding stomach
Photo: Getty

Pregnancy hormones are an amazing and—at times—mysterious thing. These powerful chemicals don't just grow a human being, they affect your mind and body. They also play a big a role in things like morning sickness and heartburn. In short, your changing hormones will impact you (and your baby) in more ways than one. But knowledge is power, so read on as Michele Hakakha, M.D., an obstetrician and co-author of Expecting 411, guides you through the ways in which six key hormones change while you're expecting.

HCG

What It Does:

HCG (Human Chorionic Gonadotropin) is the key hormone during pregnancy. It's produced by what ultimately becomes the placenta. The basic job of HCG is to tell the body that there's life growing in the womb and that the body needs to build a nest for it. HCG also tells the ovaries to shut off the production line of maturing an egg every month.

The Down Side: No one is entirely sure what causes morning sickness, but many doctors believe it is most likely connected to your rising HCG levels, i.e. pregnant people with higher levels of HCG often experience more nausea and vomiting.

HCG Levels During Pregnancy

HCG levels rise eight days after ovulation, peak at 60 to 90 days, and then lower slightly, leveling off for the remainder of the pregnancy. Typically, during the first 10 weeks of your 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 that indicates you are, indeed, pregnant).

Progesterone

What It Does:

Progesterone is made early in pregnancy by a cyst on the ovary called the corpus luteum. The corpus luteum continues to produce progesterone until about 10 weeks, when its production is taken over by the placenta.

The Down Side: Progesterone relaxes all smooth muscle (most important, the muscle wall of the uterus or "womb") in the body. It also leads to relaxation of the blood vessels throughout the body, prompting lower than normal blood pressure and occasionally dizziness, as well as gastrointestinal symptoms like heartburn, reflux, belching, nausea, vomiting, gas, and constipation. Progesterone can also increase hair growth. You may notice unwanted hair on your breasts and lower abdomen, for example.

Progesterone Levels During Pregnancy

In the first trimester, levels of progesterone rise exponentially, and then they plateau. Progesterone does some very important jobs along the way: It keeps the uterus muscle relaxed and your helps body's immune system tolerate foreign DNA (that is, the fetus)

Estrogen

What It Does:

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

The role of estrogen is super-important: It helps to stimulate hormone production in the fetus's adrenal gland, it stimulates growth of the adrenal gland, and it enhances the uterus, enabling it to respond to oxytocin (another pregnancy hormone; see below). It also prepares your breasts for milk production by enlarging the milk ducts.

Estrogen Levels During Pregnancy

Once you've reached the end of the first trimester, your body has higher levels of circulating estrogen, and then the levels plateau. Elevated estrogen levels, however, may prompt spider veins, nausea, increased appetite, and skin changes. That said, some are lucky enough to experience the upside of a pregnancy 'glow,' which is largely attributed to estrogen levels.

Relaxin

What It Does:

Relaxin is believed to be responsible for loosening the ligaments that hold the pelvic bones together and for relaxing the uterine muscle. This prepares your body for baby's passage through the birth canal. The pregnancy hormone also relaxes the arteries, so they can handle pregnancy's increased blood volume without sending your blood pressure through the roof.

The Down Side: You may feel that your ligaments are 'looser,' including your shoulders, knees, hips, and ankles, which can result in aches, pain, inflammation, and even clumsy tendencies.

Relaxin Levels During Pregnancy

While expecting, individuals have 10 times the normal amount of relaxin in their bodies.

Oxytocin

What It Does:

Oxytocin is also a hormone that stretches, though it stretches the cervix (not the pelvis) and stimulates the nipples to produce milk.

Oxytocin Levels During Pregnancy

Many believe oxytocin is the hormone that triggers labor. (Pitocin, the drug usually given to induce labor, is the synthetic form of oxytocin.) In truth, oxytocin levels don't rise as labor begins; the uterus simply becomes very sensitive and responsive to oxytocin as you progress towards the end of pregnancy.

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), and this may be linked to oxytocin as well as to other hormones and steroids. During delivery, huge bursts of oxytocin run through the brain.

Prolactin

What It Does:

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

Prolactin Levels During Pregnancy

Prolactin levels increase 10 to 20 times during pregnancy.

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