Preterm labor

Definition

Preterm labor is characterized by contractions or irritability of the uterus between weeks 20-36 of gestation that cause effacement and/or dilatation of the cervix.

Description

The usual length of a human pregnancy is from 37 to 42 weeks after the first day of the last menstrual period. The baby is more likely to survive and be healthy if it remains in the uterus for the full term of the pregnancy. Between eight to ten percent of births in the United States are preterm births. Preterm labor is the greatest cause of newborn illness and death in the United States.

Causes and symptoms

The causes of preterm labor are often not identifiable. Women with a previous history of preterm labor have the highest risk of developing it again, between 17 and 37%. Other risk factors are: low socioeconomic status, minority race, maternal age less than 18 or greater than 40, premature rupture of membranes (bag of waters), multiple gestation (twins, triplets, etc.), harmful maternal behaviors (smoking, drug use, alcohol use, no prenatal care ), uterine abnormalities (fibroid tumor, abnormally shaped uterus, incompetent cervix, exposure to diethylstilbestrol—their mothers took DES when they carried them), infectious causes (infection of the uterus, kidney infection), fetal causes (intrauterine fetal death, intrauterine growth retardation, birth defects), and abnormal implantation of the placenta.

The symptoms of preterm labor can include contractions of the uterus or tightening of the abdomen occurring every 10 minutes or more often. The uterine contractions of preterm labor, sometimes painful, will usually increase in frequency, duration, and intensity. Other symptoms associated with preterm 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, the 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 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 pelvic examination and ask about the timing and intensity of the contractions. A physician or nurse will conduct a vaginal examination and determine if the cervix has started to dilate or efface. An ultrasound technician may proceed with a transvaginal ultrasound (ultrasound of the vagina by use of a probe that is inserted into the vagina), to measure cervical length. A cervical length of < 0.98-1.18 in (2.5-3.0 cm) is associated with preterm labor.

Urine may be collected to screen for infection. A cervical culture or a wet smear may also be done to look for infection. Presence of fetal fibronectin in vaginal and cervical secretions, between 24 and 24 weeks gestation, may indicate impending preterm labor. Fibronectin is a substance that functions as an adhesive between the fetal membranes and the underlying decidua.

A fetal heart monitor is placed on the mother's abdomen to record the heartbeat of the fetus and to time the contractions. Occasionally the woman will have home monitoring of contractions and fetal activity.

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. Another test, amniocentesis , may be done to determine if the baby's lungs are mature. During an amniocentesis, a needle-like tube is inserted through the mother's abdomen into the uterus to draw out some of the fluid surrounding the fetus (amniotic fluid). 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.

Treatment

The goal of treatment is to stop preterm labor and to prevent the fetus from being delivered prior to term. A first recommendation may be for the woman with premature contractions to lie down and to drink water 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 (Bricanyl), ritodrine (Yutopar), magnesium sulfate, nifedipine (Procardia), or indomethacin (Indocin) are administered to delay delivery. When used to treat preterm labor, these medications are called tocolytic agents. Unfortunately, no study has conclusively demonstrated that the use of tocolytic drugs has significantly improved neonatal outcome. Medications used to treat preterm labor can have maternal and fetal side effects. Magnesium sulfate can lead to pulmonary edema , profound muscular paralysis , and respiratory depression. Terbutaline and Ritodrine can cause arrhythmias and hypoglycemia as well as pulmonary edema. Pregnant women who are treated with these medications need to be monitored closely in a hospital environment.

An advantage of tocolysis is in delaying delivery so that drugs that will enhance fetal lung maturity can be administered. A delay in delivery also allows for transfer to a tertiary facility that is equipped to care for premature babies. The preferred drugs to stimulate lung maturity are dexamethasone and betamethasone, corticosteroids that promote the fetal production of surfactant after 24 hours of administration. The benefit of these corticosteroids will last up to seven days, at which time the medications can be readministered.

If a vaginal or urinary tract infection is detected, antibiotic therapy is usually indicated. Antibiotics may briefly prolong the pregnancies of women who have ruptured their membranes.

Prognosis

Once symptoms of preterm labor occur during the pregnancy, the mother and fetus need to be monitored regularly. 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 chances of survival.

Health care team roles

Prior to initiating tocolytic medications, it is important to obtain such baseline laboratory test results as hematocrit , serum glucose, potassium, sodium chloride, and carbon dioxide levels. An electrocardiogram is frequently ordered because tocolytic drugs can cause an increased heart rate (tachycardia) and sometimes arrhythmias. An external uterine and fetal monitor should be put in place, and often monitors of maternal vital signs are also applied. Accurate fluid intake and output measurements are important in detecting the development of pulmonary edema (fluid in the lungs).

Other potentially serious complications of tocolytic therapy include: low blood pressure (hypotension), cardiac arrest, respiratory depression, low potassium, high blood sugar, maternal death, kidney failure, hepatitis, and gastrointestinal bleeding.

Ritodrine is a drug that is sometimes used in the management of preterm labor. To administer the medication accurately, it should be delivered as a piggyback to a main intravenous solution that goes through an infusion

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.

Decidua —The part of the lining of the uterus that sloughs off during menstruation.

pump and a microdrip tubing set. To avoid hyperglycemia, a potential side effect, the woman should receive few IV solutions containing dextrose. The ritodrine drip is increased gradually, usually every 10 minutes until uterine contractions cease, the maximum dose is reached, and/or side effects become too intense. The nurse should assess the patient's vital signs every 15 minutes during titration, and then every 30 minutes until uterine contractions stop. Ask the patient to inform the health care provider if she starts to experience any chest pain or shortness of breath. The health care provider should listen to the lungs for any abnormal breath sounds that could indicate the development of pulmonary edema. A heart rate greater than 120 beats per minute (bpm), a blood pressure lower than 90/60, and any cardiac arrhythmias should be reported immediately. Continue to monitor laboratory values every four hours. The fetal response to contractions and medication administration should be monitored continuously. Closely monitor daily weights to assess for possible pulmonary edema resulting from fluid retention. If therapy with ritodrine is successful in halting uterine contractions, then oral administration of ritodrine or terbutaline will often be ordered. Other tocolytic medications that are delivered in a similar manner are magnesium sulfate, subcutaneous terbutaline, nifedipine, and indomethacin.

Patient education

Health care professionals should educate all pregnant women about the signs and symptoms of preterm labor, ensuring an understanding of even the more subtle symptoms. Pregnant women should be alert for symptoms that could be indicative of preterm labor, such as constant, dull, low back pain; vaginal spotting; pelvic pressure and/or tightening of the abdomen; increased vaginal discharge; and intestinal-like cramping.

Pregnant women who are at home on bed rest should be given the following instructions:

• Stay on bed rest except to get up to use the bathroom.
• Drink eight to ten glasses of liquids a day.
• Do not engage in such activities as nipple stimulation that could trigger contractions.
• Do not engage in sexual activities, including masturbation.
• Promptly inform the health care provider if the membranes rupture (sudden gush of vaginal fluid) or if there is any vaginal bleeding.
• Communicate to the health care provider any symptoms of a urinary tract infection (burning on urination and frequent urination) or of a vaginal infection (vaginal burning, itching or discomfort).

Prevention

Smoking, poor nutrition , and drug or alcohol abuse can increase the risk of premature labor and early delivery. Smoking, drug and 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 to receive regular prenatal examinations throughout the pregnancy. The health care provider should be informed of any medications that the mother is receiving and any maternal health conditions.

Resources

BOOKS

Pillitteri, Adele. Maternal & Child Health Nursing, 3rd ed.Philadelphia: Lippincott, 1999.

PERIODICALS

Weismiller, David G. "Practical Therapeutics: Preterm Labor."American Family Physician 59, number 3 (February 1,1999).

ORGANIZATIONS

The March of Dimes Resource Center. (888) 663-4637 (888-MODIMES). <http://www.modimes.org>.

OTHER

"Am I in Labor?" in Iowa Health Book: Obstetrics and Gynecology at The Virtual Hospital. <http://www.vh.org>.

Nadine M. Jacobson, R.N.