Ah, the ever-changing hormones of pregnancy. They play about as big a role in the next nine months as do morning sickness and heartburn. 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 during your nine months.
What it does: HCG is the key hormone that's present during pregnancy. It's produced by what ultimately becomes the placenta. Its basic job is to tell a woman's body that there is a life form growing in her womb and that her 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. 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).
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. 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 plays a role in the immune system helping the body tolerate foreign DNA (that is, the fetus).
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 all the not-so-fun gastrointestinal symptoms of pregnancy that include 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.
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, with several organs and other bodily systems in the fetus triggered into development by estrogen. Once you've reached the end of the first trimester, your body has higher levels of circulating estrogen, and then the levels plateau. 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 mother's uterus, enabling it to respond to oxytocin (another pregnancy hormone; see below).
The downside: Elevated estrogen levels may also prompt spider veins, nausea, increased appetite, and skin changes including changes in skin's pigment. Some women, however, are lucky enough to experience the upside of a pregnancy 'glow,' which is largely attributed to estrogen levels.
What it does: Many women 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, it's just that the uterus becomes very sensitive and responsive to oxytocin as you progress towards the end of pregnancy. Oxytocin is also the hormone that stretches the cervix and stimulates the nipples to produce milk.
What it does: This milk-producing hormone -- which increases 10 to 20 times during pregnancy -- has a tranquilizing effect. Prolactin prepares breast tissues for lactation and the release of milk.
What it does: Relaxin is believed to be responsible for loosening up the ligaments that hold the pelvic bones together and for relaxing the uterine muscle, both in preparation for delivering your baby through the birth canal. During pregnancy women have 10 times the normal amount of this pregnancy hormone in their bodies.
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.
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