premature labor

Premature Labor 

Definition

Premature labor is the term to describe contractions of the uterus that begin at weeks 20-36 of a pregnancy.

Description

The usual length of a human pregnancy is 38-42 weeks after the first day of the last menstrual period. Labor is a natural series of events that indicate that the birth process is starting. Premature labor is defined as contractions that occur after 20 weeks and before 37 weeks during the term of pregnancy. The baby is more likely to survive and be healthy if it remains in the uterus for the full term of the pregnancy. It is estimated that around 10% of births in the United States occur during the premature period. Premature birth is the greatest cause of newborn illness and death. In the United States, prematurity has a greater impact on African-Americans.

Causes and symptoms

The causes of premature labor cannot always be determined. Some research suggests that infection of the urinary or reproductive tract may stimulate premature labor and premature births. Multiple pregnancies (twins, triplets, etc.) are more likely to result in to premature labor. Smoking, alcohol use, drug abuse, and poor nutrition can increase the risk of premature labor and birth. Adolescent mothers are also at higher risk for premature delivery. Women whose mothers took diethylstilbestrol (DES) when they carried them are more likely to deliver prematurely, as are women who have had previous surgery on the cervix.

The symptoms of premature labor can include contractions of the uterus or tightening of the abdomen, which occurs every ten minutes or more frequently. These contractions usually increase in frequency, duration, and intensity, and may or may not be painful. Other symptoms associated with premature labor can include menstrual-like cramps, abdominal cramping with or without diarrhea, pressure or pain in the pelvic region, low backache, or a change in the color or amount of vaginal discharge. As labor progresses, the cervix or opening of the uterus will open (dilate) and the tissue around it will become thinner (efface). Premature rupture of membranes (when the water breaks) may also occur.

An occasional contraction can occur anytime during the pregnancy and does not necessarily indicate that labor is starting. Premature contractions are sometimes confused with Braxton Hicks contractions, which can occur throughout the pregnancy. Braxton Hicks contractions do not cause the cervix to open or efface, and are considered "false labor."

Diagnosis

The health care provider will conduct a physical examination and ask about the timing and intensity of the contractions. A vaginal examination is the only way to determine if the cervix has started to dilate or efface. Urine and blood samples may be collected to screen for infection. A vaginal culture (a cotton-tipped swab is used to collect some fluid and cells from the vagina) may be done to look for a vaginal infection. A fetal heart monitor may be placed on the mother's abdomen to record the heartbeat of the fetus and to time the contractions. A fetal ultrasound may be performed to determine the age and weight of the fetus, the condition of the placenta, and to see if there is more than one fetus present. Amniocentesis will sometimes be performed. This is a procedure where a needle-like tube is inserted through the mother's abdomen to draw out some of the fluid surrounding the fetus. Analysis of the amniotic fluid can determine if the baby's lungs are mature. A baby with mature lungs is much more likely to survive outside the uterus.

Key terms

Braxton Hicks contractions — Tightening of the uterus or abdomen that can occur throughout pregnancy. These contractions do not cause changes to the cervix and are sometimes called false labor or practice contractions.

Cervix — The opening at the bottom of the uterus, which dilates or opens in order for the fetus to pass into the vagina or birth canal during the delivery process.

Contraction — A tightening of the uterus during pregnancy. Contractions may or may not be painful and may or may not indicate labor.

Treatment

The goal of treatment is to stop the premature labor and prevent the fetus from being delivered before it is full term. A first recommendation may be for the woman with premature contractions to lie down with feet elevated and to drink juice or other fluids. If contractions continue or increase, medical attention should be sought. In addition to bed rest, medical care may include intravenous fluids. Sometimes, this extra fluid is enough to stop contractions. In some cases, oral or injectable drugs like terbutaline sulfate, ritodrine, magnesium sulfate, or nifedipine must be given to stop the contractions. These are generally very effective; however, as with any drug therapy, there are risks of side effects. Some women may need to continue on medication for the duration of the pregnancy. Antibiotics may be prescribed if a vaginal or urinary tract infection is detected. If the membranes have already ruptured, it may be difficult or impossible to stop premature labor. If infection of the membranes that cover the fetus (chorioamnionitis) develops, the baby must be delivered.

Prognosis

If premature labor is managed successfully, the pregnancy may continue normally for the delivery of a healthy infant. Once symptoms of preterm labor occur during the pregnancy, the mother and fetus need to be monitored regularly since it is likely that premature labor will occur again. If the preterm labor cannot be stopped or controlled, the infant will be delivered prematurely. These infants that are born prematurely have an increased risk of health problems including birth defects, lung problems, mental retardation, blindness, deafness, and developmental disabilities. If the infant is born too early, its body systems may not be mature enough for it to survive. Evaluating the infant's lung maturity is one of the keys to determining its chance of survival. Fetuses delivered further into pregnancy and those with more mature lungs are more likely to survive.

Prevention

Smoking, poor nutrition, and drug or alcohol abuse can increase the risk of premature labor and early delivery. Smoking and drug or alcohol use should be stopped. A healthy diet and prenatal vitamin supplements (prescribed by the health care provider) are important for the growth of the fetus and the health of the mother. Pregnant women are advised to see a health care provider early in the pregnancy and receive regular prenatal examinations throughout the pregnancy. The health care provider should be informed of any medications that the mother is receiving and any health conditions that exist before and during the pregnancy.

Resources

Organizations

March of Dimes Birth Defects Foundation. 1275 Mamaroneck Ave., White Plains, NY 10605. (914) 428-7100. resourcecenter@modimes.org. http://www.modimes.org.

Other

"Am I in Labor?" The Virtual Hospital Page. University of Iowa. http://www.vh.org.

---

labor /la·bor/ (la´ber) [L.] the function of the female by which the infant is expelled through the vagina to the outside world: the first stage begins with onset of regular uterine contractions and ends when the os is completely dilated and flush with the vagina; the second extends from the end of the first stage until the expulsion of the infant is completed; the third extends from expulsion of the infant until the placenta and membranes are expelled; the fourth denotes the hour or two after delivery, when uterine tone is established.

---

artificial labor  induced l.

dry labor  that in which the amniotic fluid escapes before the onset of uterine contractions.

false labor  see under pain.

induced labor  that brought on by mechanical or other extraneous means, usually by the intravenous infusion of oxytocin.

missed labor  that in which contractions begin and then cease, the fetus being retained for weeks or months.

postmature labor , postponed labor that occurring two weeks or more after the expected date of confinement.

precipitate labor  that occurring with undue rapidity.

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 week.

---

premature labor

n.

The onset of labor before the 37th completed week of pregnancy.

---

premature labor.

See preterm labor.

---

labor [la´ber]

the physiologic process by which the uterus expels the products of conception (fetus or newborn and placenta), after 20 or more weeks of gestation. It may be divided into three stages: The first stage (dilatation) begins with the onset of regular uterine contractions and ends when the cervical os is completely dilated and flush with the vagina, thus completing the birth canal. The second stage (expulsion) extends from the end of the first stage until the expulsion of the infant is completed. The third stage (placental stage) extends from the expulsion of the child until the placenta and membrane are expelled and contraction of the uterus is completed. Called also accouchement and parturition.

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).

First Stage of Labor. The beginning of labor is usually indicated by one or more of the following signs: (1) show (passage from the vagina of small quantities of blood-tinged mucus); (2) breaking the “bag of waters” (normal rupture of membranes, indicated by a gush or slow leakage of amniotic fluid from the vagina); and (3) true labor contractions. The first two of these signs are almost always unmistakable. The contractions, however, can be confusing. braxton-hicks contractions, or “false labor pains,” can be distinguished from true labor contractions by the irregular time intervals between them and by their tendency to disappear when the patient changes position or gets up and walks about. True labor contractions are regularly spaced and usually start in the small of the back, or as a feeling of tightness in the abdomen, or of pressure in the pelvis. The contractions recur at shorter and shorter intervals, every three to five minutes, and become progressively stronger and longer lasting. The increase in the strength of contractions usually is accompanied by an increase in the amount of show because of rupture of capillaries in the dilating cervix.

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.

Patient Care. Once labor has begun the patient should have someone in constant attendance. She will derive much emotional support from one who is warm, kind, and understanding, and displays a genuine interest in her welfare and that of her infant. It is best to have the same person care for her through the entire labor and birth process.

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.)

Schematic representation of factors believed to have a role in starting labor. From Gorrie et al., 1994.

artificial labor induced labor.

dry labor a lay term indicating that in which the amniotic fluid escapes before contraction of the uterus begins.

false labor false pains.

induced labor that which is brought on by extraneous means, e.g., by the use of drugs that cause uterine contractions; called also artificial labor.

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.

preterm labor labor commencing before the end of 37 completed weeks of gestation; it can be arrested (see tocolysis) and does not necessarily lead to preterm delivery. Preterm labor can be treated by bed rest at home and use of a tokodynamometer with a recording unit that transmits data about uterine activity over the telephone to a monitoring station. Tocolytic drugs, including ritodrine hydrochloride and terbutaline, may be used to relax the uterine muscles.

spontaneous labor delivery occurring without artificial aid.