Hormones play a huge role in pregnancy and in the birth process. Here is an overview of hormonal interactions.
hCG: The early chorionic villi of the implanted ovum secrete human chorionic gonadotropin (hCG), which prolongs the life of the corpus luteum. The result is the continued production of estrogen and progesterone, which are necessary to maintain the endometrium. During pregnancy, hCG appears in maternal blood and is excreted in the mother's urine, allowing diagnosis of pregnancy by tests.
hPL: The chorionic cells of the placenta produce another hormone, human chorionic somatomammotropin which is also known as human placental lactogen (hPL). This hormone influences somatic cell growth of the fetus and facilitates preparation of the breasts for lactation.
The increase in hCG and hPL in the mother is thought to be responsible for many important changes during pregnancy such as growth of the uterus and the development of the breast duct system. Estrogen is also helpful in breast duct system development and progesterone is valuable in the development of the lobule-alveolar system.
The pituitary gland enlarges during pregnancy and is the source of production of oxytocin. The posterior lobe is the primary source of oxytocin, which has a stimulating effect on the uterine muscle and lactation.
The adrenal cortex increases in activity during pregnancy. The secretion of cortisol by the adrenals does not change yet the metabolism of cortisol is changed as a result of estrogen. There is an increase in aldosterone production by the adrenal glands and this hormone results in the decreased ability of the kidneys to handle salt during pregnancy. This leads to some fluid retention or edema.
Relaxin is produced by the ovaries and is primarily responsible for softening ligaments and cartilage. The softening of cartilage, especially in late pregnancy, is the cause of suprapubic discomfort, waddling, and the ability of the pelvis to spread during the birth process.
According to Pregnancy Childbirth and the Newborn by Simkin, Whalley and Keppler, "Caffeine causes an increased production of the stress hormones epinephrine (adrenalin) and norepinephrine (noradrenalin). These hormones constrict peripheral blood vessels, including those in the uterus, which results in a temporary decrease in the amount of oxygen available to the fetus." Fear and anxiety during labor can also facilitate the release of these two hormones, resulting in the prolonging or cessation of labor, most commonly at the 5 cm point.
Often mistaken as hormones, endorphins are naturally occurring opiate-like substances that influence the transmission of pain impulses. Possibly neurotransmitters, endorphins present at the synapses of nerve cells result in the cessation of pain. Failure to release endorphins allows pain to occur. When pain medication is administered, natural endorphins are not produced. As the medication subsides, the natural endorphin level is not matching the pain sensation, which has been rising. This is the reason why when an epidural is turned off to allow the client a chance to push with her urge to push, the pain of the contractions is nearly overwhelming. It is important to note that it is theorized that endorphin production may be inherited and may be stimulated by a variety of alternative therapies such as massage and acupressure.