Labor is believed to be triggered by the release of oxytocin and prostaglandins, after a fall in the levels of other hormones. Normally at the end of pregnancy oxytocin, which is stored in the posterior lobe of the pituitary gland, is released and stimulates contraction of the uterine muscles.
The progress and final outcome of labor are influenced by four factors: (1) the “passage” (the soft and bony tissues of the maternal pelvis); (2) the “powers” (the contractions or forces of the uterus); (3) the “passenger” (the fetus); and (4) the “psyche” (mother’s emotional state, e.g., anxiety).
The mechanisms of labor (for a vertex presentation) consist of the following sequence of events: engagement (posterior occiput of fetus enters the pelvic outlet); flexion (of fetal head); descent (fetal head descends lower into the midpelvis); internal rotation (fetal head and body rotate so that the occiput is more anterior); extension (fetal head extends once the occiput is beneath the symphysis pubis); and external rotation (fetal head rotates back to position it had at engagement).
This first stage of childbirth is known as the dilatation period. The uterus is like a large rubber bottle with a half-inch long neck that is almost closed. As the uterine muscles contract, the cervix becomes thinner (effacement) and more open (dilated) so that the neck of the uterus eventually resembles that of a jar more than that of a bottle.
The length of the first stage of labor varies with each individual patient, with an average of 8 to 12 hours in primiparous and 6 to 8 hours in multiparous women. It is related to the strength and effectiveness of the contractions and is a period when the mother is instructed to relax as much as possible and let the uterus do the work. Pushing or bearing down is not effective during this stage and is harmful in that it may cause a tearing of the cervix and will only serve to exhaust the woman. She is encouraged to rest and possibly to nap between contractions.
The second stage of labor may be heralded by symptoms of nausea, vomiting, irritability, the urge to bear down, or periods of feeling hot and then cold, signs of the period of transition from the first to the second stage.
Second Stage of Labor. This period, called the expulsion stage, usually is characterized by intense contractions that last for about one full minute and occur at 2 to 3 minute intervals. The cervix is fully dilated and the woman is able to help with this process by bearing down with each uterine contraction, using her abdominal muscles to help expel the infant. This stage varies from a few minutes to one to two hours.
Third Stage of Labor. In this stage the placenta detaches itself from the uterine wall and is expelled. The process takes about 15 minutes, and is painless.
Fourth Stage of Labor. This final stage is the stage of recovery and lasts 2 to 4 hours.
During labor the strength, frequency, and duration of contractions are noted and recorded. It is expected that the contractions will increase in all three characteristics, but a sudden change in any one should be reported to the health care provider immediately. The rate, regularity, and volume of the fetal heart tones are checked and recorded periodically. Some apprehensive patients may be helped by allowing them to listen to the infant’s heartbeat.
Food and fluids are withheld during active labor, but thirst may cause some discomfort and may be lessened by allowing the patient to moisten her lips with a gauze sponge or to suck on ice chips. Intravenous fluids are usually given. Frequent bathing of the face with a cool washcloth often helps relieve the flushed feeling brought about by the actual hard work being done by the mother. Frequent changing of her gown and of the pad protecting the bed linens may be necessary to keep her clean, dry, and comfortable.
If there is a support person with the woman during labor, that person should be instructed in ways he or she can help the patient and at the same time feel that he or she is making some contribution in this very important event. The support person may wish to participate in keeping a record of the contractions, or might appreciate the opportunity to listen to the fetal heart tones occasionally. If the patient feels that sacral support during each contraction helps mitigate the pain, the support person can be shown how to do this. Some supporters have attended classes for expectant parents and are prepared for their role during labor and delivery. Both the patient and the support person should be informed of the progress during labor so they can feel that something is being accomplished by their efforts.
The patient is encouraged to rest and relax between contractions so as to conserve her strength. She should not bear down until the cervix is fully dilated, since this effort will only serve to exhaust her and may cause lacerations of the cervix. After the cervix is fully dilated she can speed the birth process by holding her breath and contracting her abdominal muscles. Controlled breathing exercises learned in classes for expectant parents promote relaxation and aid labor.
Although serious complications rarely develop during labor, they can occur and must be watched for. Observations to report immediately include hyperactivity of the fetus; vaginal bleeding in excess of a heavy show; a rapid and irregular pulse and drop in blood pressure; sudden rise in blood pressure; and headache, visual disturbances, extreme restlessness, or rapidly developing edema. A sudden cessation of contractions or a contraction that does not relax may indicate a serious disturbance in the labor process. The appearance of meconium in the vaginal discharge may indicate fetal distress unless the infant is in a breech position. (See also fetal monitoring.)
dry labor a lay term indicating that in which the amniotic fluid escapes before contraction of the uterus begins.
false labor false pains.
instrumental labor delivery facilitated by the use of instruments, particularly forceps.
missed labor that in which contractions begin and then cease, the fetus being retained for weeks or months.
precipitate labor delivery accomplished with undue speed.
premature labor expulsion of a viable infant before the normal end of gestation; usually applied to interruption of pregnancy between the twenty-eighth and thirty-seventh weeks.
spontaneous labor delivery occurring without artificial aid.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.