preterm labor

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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.

preterm labor

labor that occurs earlier in pregnancy than normal, either before the fetus has reached a weight of 2000 to 2500 g or before the 37th or 38th week of gestation. No single measure of fetal weight or gestational age is used universally to designate preterm birth; local or institutional policy dictates which of several standards is applied. Prematurity is a concomitant of 75% of births that result in neonatal mortality. It may occur spontaneously, or it may be iatrogenic. The incidence of preterm labor increases in inverse proportion to maternal age, weight, and socioeconomic status. Incidence is higher for African-American women, women who have not had adequate prenatal care or have an abnormal obstetric history, and women who smoke or whose diet is deficient in protein or calories. Predisposing conditions include maternal infection, low weight gain, uterine bleeding, multiple gestation, polyhydramnios, uterine abnormalities, incompetent cervix, premature rupture of membranes, and intrauterine fetal growth retardation. The cause of preterm labor is poorly understood; in some cases there may be several contributing causes. In some pregnancies preterm labor may be homeostatic, resulting in the best possible outcome under the particular abnormal conditions. If preterm labor itself constitutes a threat to the fetus, the outcome of pregnancy may be improved if labor can be inhibited. Determining accurately which pregnancies are likely to benefit from the inhibition of labor and which are not is difficult. Medications used to stop labor are not always effective. Misdiagnosis of gestational age and fetal condition may lead to induction of labor that is inadvertently premature; preterm babies whose birth has been brought about inappropriately early account for 15% of admissions to newborn intensive care nurseries. Also called premature labor. See also small for gestational age infant.

Preterm labor

Labor before the thirty-seventh week of pregnancy.
Mentioned in: Incompetent Cervix

Preterm Labor

DRG Category:775
Mean LOS:2.4 days
Description:MEDICAL: Vaginal Delivery Without Complicating Diagnoses
DRG Category:778
Mean LOS:3.1 days
Description:MEDICAL: Threatened Abortion

Preterm labor (PTL) is labor that occurs after the completion of the 20th week and before the beginning of the 37th week of gestation. To be considered PTL, the uterine contractions must occur at a frequency of four in 20 minutes or eight in 60 minutes. Spontaneous rupture of the membranes often occurs in PTL. If the membranes are intact, documented cervical change (80% effacement or > 1 cm dilation) must be noted during a vaginal examination for the situation to be classified as PTL.

PTL has a poorly understood etiology, unclear mechanisms, and an absence of medical consensus related to diagnosis and treatment. This is unfortunate because preterm birth is the second-highest cause of the high infant morbidity and mortality rate in the United States (birth defects is the first). Preterm birth occurs in approximately 12% of pregnancies in the United States, and the risk of having a recurrent preterm birth after one, two, or three occurrences is 15%, 30%, and 45%, respectively. The major fetal risk of preterm delivery is related to immaturity of the lungs and respiratory system. Preterm infants can have many other problems as well, such as neurological complications, thermoregulation problems, and immaturity of major organ systems. Maternal risks of PTL are related to the pharmacologic treatment involved in stopping the labor.


In many cases, the cause cannot be identified. Preterm premature rupture of membranes occurs in about one-third of the cases, but its causes are also unknown. Intrauterine, genital tract, and/or periodontal infection can precede or follow premature rupture of membranes. Infectious processes that occur prior to and early in pregnancy are thought to be linked to PTL/rupture of membranes owing to the inflammatory response that weakens the fetal membranes. There is also evidence that an idiopathic, undiagnosed PTL leads to microbial invasion owing to a breakdown in the cervical barrier function, and this eventually manifests itself as chorioamnionitis and true clinical PTL. Several risk factors have been identified (Box 1).

Risk Factors for Preterm Labor

Table .
  • Preterm labor
  • Preterm delivery
  • Cone biopsy
  • Induced or habitual abortions
  • Diethylstilbestrol exposure
  • Uterine leiomyomas or cervical anomalies
  • Renal disease
  • Hypertension
  • Prepregnancy weight < 100 lb
    Obstetric Related
  • Cervical incompetence
  • Placenta previa or abruption
  • Uterine distention (hydramnios, twins, large for gestational age [LGA] fetus)
  • Maternal infection (periodontal, genital tract, chorioamnionitis)
  • Abdominal surgery during pregnancy
  • Smoking, alcohol, drug use during pregnancy
    Fetal Related
  • Multiple gestation
  • Fetal anomalies

Genetic considerations

Genetic contributions are unclear.

Gender, ethnic/racial, and life span considerations

Women who are younger than 17 or older than 35 are more likely to have PTL. PTL is more prevalent in African Americans than in European Americans; it is also associated with low socioeconomic status, low educational level, domestic violence, and single parenthood.

Global health considerations

No data available.



Ask the date of the patient’s last menstrual period to estimate delivery date. If the patient reports using cigarettes, alcohol, or other harmful substances, determine the amount and frequency. Ask about the onset of contractions and their frequency, duration, and intensity (Box 2).

Signs and Symptoms of Preterm Labor
  • Uterine contractions (painful or painless), cramping, lower back pain
  • Feeling of pelvic pressure or fullness
  • Change in the amount or character of amniotic fluid
  • Bloody show
  • Gastrointestinal upset: Nausea, vomiting, diarrhea
  • General sense of discomfort or “just feeling bad”
  • Sensation that baby is frequently “balling up”

Have the patient describe the contractions; sometimes false labor is felt in the lower abdomen and is irregular. Ask if the patient feels the baby move. Ask about any medical problems because some pharmacologic treatment may be contraindicated in certain instances (cardiac disease, hypertension, renal disease, uncontrolled diabetes, and asthma).

Physical examination

The most common symptoms are uterine contractions of sufficient frequency and intensity to cause progressive cervical dilation and effacement. A thorough initial examination is needed to help determine if the patient is in PTL or in false labor. Apply a fetal monitor to determine the frequency and duration of contractions. Palpate the fundus of the uterus; if the patient is having PTL, note uterine firmness. Obtain the fetal heart rate with an electronic fetal monitor, noting baseline, presence or absence of accelerations or decelerations, and variability. After checking with the physician, perform a sterile vaginal examination to determine dilation, station, and effacement. Note any vaginal bleeding, bloody show, or leakage of amniotic fluid. Nitrazine (pH) paper can be used during the examination to detect if the membranes have ruptured (paper turns blue because pH is alkaline). Note that an elevated temperature indicates infection or dehydration.


The reality of a premature delivery and a sick newborn in a neonatal intensive care unit (NICU) creates a tremendous amount of stress and emotion for the parents and significant others. Assess the patient’s and the significant others’ abilities to cope. The patient may experience guilt, suspecting that she did something wrong during the pregnancy to precipitate the labor.

Diagnostic highlights

General Comments: PTL is generally diagnosed by the presence of contractions accompanied by cervical change. Testing is done to examine the possibility of delivery and cervical ripeness.

TestNormal ResultAbnormality With ConditionExplanation
Fetal fibronectinAbsent in cervicovaginal secretions between 20 and 37 wkPositiveIf positive, 60% will deliver within 1 wk; if negative, 99.3% will not deliver within 1 wk
Cervical length (via transvaginal ultrasound)> 30 mm at 24 wk; no evidence of a bulging bag of water or leakage of fluid< 25 mm (10th percentile) or evidence of funneling at 24 wk or leaking of the amniotic fluid at the internal osCervical effacement labor

Other Tests: Pregnancy test, abdominal ultrasound to assess the size and well-being of the infant, Doppler fetal heart tones, amniocentesis to obtain amniotic fluid to perform tests to determine fetal lung maturity (lecithin-to-sphingomyelin ratio, phosphatidylglycerol, surfactant-to-albumin ratio), complete blood count, vaginal/cervical/urine cultures (infections often precede PTL)

Primary nursing diagnosis


Fear related to uncertainty of outcome and complexity/effects of treatments


Fear control; Anxiety control; Comfort level; Coping


Labor suppression; High-risk pregnancy care; Security enhancement; Resuscitation: Fetus

Planning and implementation


The goals of treatment are to stop the contractions and to prevent the cervix from dilating, thereby avoiding delivery until at least 34 weeks. Once the cervix reaches 4 cm in dilation, treatment is stopped and the delivery is allowed to occur. Ideally, delivery is in a hospital with the expertise necessary to treat a preterm neonate.

Although they are the first strategies often employed to halt PTL, bedrest, hydration, and sedation are not supported in the literature as effective means of stopping PTL. Intravenous (IV) fluids, usually a crystalloid such as lactated Ringer’s solution and a sedative if the patient is anxious, are used. Terbutaline sulfate is often given subcutaneously, along with hydration. If the contractions stop and the labor is not progressing, patients are discharged home on complete bedrest. Home monitoring of uterine contractions with transmission of data to the physician is possible. Also, patients may be discharged with a terbutaline pump, which infuses 3 to 4 mg of terbutaline subcutaneously each day; evidence of the effectiveness of use of the pump is being evaluated.

If labor continues, IV medications are indicated. Tocolysis (inhibition of uterine contractions) is contraindicated in cases of maternal infection, pregnancy-induced hypertension, hypovolemia, and fetal distress. During the initial period of infusion of beta-adrenergic drugs, auscultate the patient’s lungs for rales and rhonchi; observe for dyspnea and chest discomfort; determine the fetal heart rate, maternal pulse, blood pressure, and respiratory rate; and monitor the status of contractions every 10 minutes. Fluid restriction, accurate monitoring of intake and output, and daily weights are indicated to monitor fluid balance.

Administer glucocorticoids concurrently with tocolytics. The incidence of respiratory distress is lower if the birth is delayed for at least 24 hours after the initiation of glucocorticoids. The effect on the lung maturity persists for 1 week after the therapy is completed. If glucocorticoids are administered concurrently, monitor the patient for signs and symptoms of pulmonary edema. If magnesium sulfate is used for tocolysis, closely monitor deep tendon reflexes; hyporeflexia occurs if the patient is becoming toxic and precedes respiratory depression. If tocolysis is successful and contractions are under control, the infusion is discontinued by gradually decreasing the rate and converting to oral administration.

Monitor the fetal heart rate variability and for the absence or presence of accelerations and decelerations. If signs of fetal stress occur, turn the patient on her left side, increase the rate of the IV hydration, administer oxygen at 10 L/minute per mask, and notify the physician.

Delivery of the preterm infant can be done vaginally or by cesarean. The decision for the method of delivery is often made jointly by the physician, neonatologist, and parents. If the fetus is very premature, often the neonatologist suggests a cesarean to prevent trauma to the fetal head and an increased risk of intraventricular hemorrhage.

Pharmacologic highlights

There are no first-line drugs to treat PTL; rather, individual patient conditions and physician preference dictate the treatment. Ritodrine, formerly the only drug approved by the U.S. Food and Drug Administration to treat PTL, has been withdrawn from the U.S. market by its manufacturer.

Medication or Drug ClassDosageDescriptionRationale
Nifedipine30 mg loading dose, 10–30 mg q 4–6 hrCalcium channel blocker; tocolyticInhibits contraction of smooth muscles by reducing intracellular calcium influx
Indomethacin100 mg PR, then mg PO every 6 hr for 8 dosesProstaglandin synthetase inhibitor; tocolytic (labor repressant)Reduces prostaglandin systhesis and decreases inflammation
Magnesium sulfate (contraindicated in myasthenia gravis)4–6 g IV loading dose, 1–4 g/hr of IV maintenanceCentral nervous system depressant; tocolyticDecreases contraction of smooth muscles by reducing intracellular calcium influx; some controversy about its effectiveness
Terbutaline (Brethine)Initially, 2.5 mcg/min; increase to a max of 20 mcg/min OR 0.25 mg SQ q 20 min × 3 doses, then q 3 hr; after IV is discontinued, follow with 5 mg PO q 4–6 hrBeta-adrenergicRelaxes smooth muscle, inhibiting uterine contractions; use has been curtailed due to side effects such as palpitations, tachycardia, and transient hyperglycemia, hypokalemia, and myocardial ischemia in the mother and fetus
Betamethasone (Celestone)12 mg IM q 24 hr × 2GlucocorticoidHastens fetal lung maturity; indicated if delivery is anticipated between 24 and 34 wk


Prevention of PTL is an important function of the nurse. During the initial prenatal visit, educate the patient on the signs and symptoms of PTL and ask the patient on subsequent visits if she is experiencing any of these indicators. If a patient reports alcohol, cigarette, or drug use any time during the pregnancy, work with her to modify her behavior. A referral to a drug-treatment, smoking-cessation, or alcohol counseling program may be indicated. Encourage patients to stay well hydrated, especially during the warm weather, because dehydration can cause contractions. In addition, nurses can become involved in community education of adolescents and women about the symptoms, risk factors, and consequences of PTL.

Admission to the hospital for PTL is often a first hospitalization for many young patients. Provide emotional support and educate the patient on simple procedures that may seem routine (drawing laboratory work, frequent assessments done by nurses and physicians, mealtimes and menus). Discuss the implications and expectations of preterm delivery. Be realistic in the discussions and, if possible, arrange for a visit to the neonatal intensive care unit and a talk with the neonatologist. Include the family in conversations with the patient and encourage them to assist with caring for the patient while she is on bedrest. Often, the patient is on bedrest for several days in the hospital and at home. While she is in the hospital, suggest diversional activities, such as videos, special visitors, and games. Encourage the woman to lay on her side to increase placental perfusion and reduce pressure on the cervix.

Evidence-Based Practice and Health Policy

Conde-Agudelo, A., & Romero, R. (2013). Transdermal nitroglycerin for the treatment of preterm labor: A systematic review and metaanalysis. American Journal of Obstetrics and Gynecology, 209(6), 551.e1–551.e18. doi 10.1016/j.ajog.2013.07.022

  • Investigators conducted a meta-analysis of 13 randomized controlled trials in which 1,302 women in preterm labor were assigned to either a transdermal nitroglycerin treatment group or a control group that was treated with a placebo (2 studies, n = 186), B2-adrenergic receptor agonist (9 studies, n = 1,024), nifedipine (1 study, n = 50), or magnesium sulfate (1 study, n = 42).
  • When compared with the B2-adrenergic receptor agonist treatment group, women in the transdermal nitroglycerin treatment group were 29% less likely to give birth before 34 weeks (95% CI, 0.51 to 0.99), and their infants had a mean increased birth weight of 331 grams.
  • There were no significant differences in neonatal outcomes between the transdermal nitroglycerin treatment group and the placebo, nifedipine, and magnesium sulfate treatment groups.

Documentation guidelines

  • Contraction status: Frequency, intensity, duration
  • Fetal heart rate: Baseline, variability, accelerations, decelerations
  • Patient’s response to bedrest and hydration
  • Patient’s response to tocolysis: Vital signs, anxiety, ability to sleep, deep tendon reflexes, lung sounds, intake and output

Discharge and home healthcare guidelines

home care if undelivered.
Discuss the importance of maintaining bedrest in the lateral position. Teach the patient to remain well hydrated, take all medications exactly as prescribed, and report any uncomfortable side effects to the physician. Teach the patient to avoid any activity that could possibly initiate labor (sexual intercourse, nipple stimulation). Explain that the patient should check daily to determine whether the fetus is moving or the uterus is contracting. Teach the patient how to palpate the fundus and judge the intensity of a contraction. Teach the patient how to use the home monitor for uterine contractions and the terbutaline pump if ordered. Review the warning signs of PTL and when she should call the physician.

home care if delivered.
Teach the patient to be aware of signs and symptoms that indicate postpartum complications: a hard, reddened area on the breast; pain in the calf of the leg; increase in bleeding; foul odor to vaginal discharge; fever; burning with urination; or persistent mood change. Teach her not to lift anything heavier than the baby and not to drive until after the postpartum checkup with the physician. Encourage her to maintain a healthy diet and adequate nutrition and to schedule rest time around the baby’s sleeping times. Elicit the help of family members if needed.

References in periodicals archive ?
To reduce the complications and the costs associated with PTL, reducing the risk factors of preterm labor in the general population besides taking certain medications (tocolysis) for inhibiting initiated uterine contractions seem to be useful strategies.
In conclusion, the remarkably similar combined data from these two independent studies suggest that analysis of circulatory fetal nucleic acids may assist obstetricians in identifying pregnant women with an increased risk of preterm labor who do indeed deliver prematurely.
Details of the labor and the clinical interventions used were recorded on either a preterm labor encounter form or a preterm delivery record, depending on whether a delivery occurred.
There have been trials that have analyzed only those women who developed preterm labor, trials that looked at the rate of preterm birth, some that looked at the intermediate outcome of cervical dilation, others that looked at the total HUAM package (both the recording device and the nurse contact).
Mothers' socioeconomic status affects pregnancy outcome, and socioeconomic inequality is one of the indicators of infant health and pregnancy outcome including preterm labor (29).
She hopes to identify key steps in normal cervical ripening, as well as differences that may be caused by infection and other factors that trigger preterm labor.
Olcese patented his theory that reducing melatonin would produce better results for women at risk of preterm labor.
Increased serum and amniotic fluid concentrations of several cytokines have been reported in women with preterm labor (8-12).
Slotkin of Duke University Medical Center and his colleagues investigated how separate and combined exposures to terbutaline, a drug used to arrest preterm labor, and to the organophosphate pesticide chlorpyrifos affect several indices of brain cell growth and function.
The only other significant predictors of preterm labor in this study were a prior preterm delivery and antiretroviral treatment for less than 10 weeks.
Among the women in the sample, 824 experienced one of the adverse pregnancy outcomes studied: 126 antepartum hemorrhage, 233 preterm labor, 308 preterm delivery, 134 intrauterine growth restriction and 23 perinatal death.
Mothers given magnesium sulfate as a tocolytic as an attempt to stop preterm labor contractions may be more likely to have babies with negative outcomes.