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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