Management

Hydration appears to decrease the frequency of preterm contractions, but it does not decrease the rate of preterm birth. Intermittent digital cervical examinations should be performed either to confirm the diagnosis of preterm labor or to monitor progression. The frequency of these examinations has not been established and should be based on the clinical situation. However, a digital examination should always be performed at discharge to assess any cervical change.

If preterm delivery is a possibility, antibiotic prophylaxis for group B streptococci should be administered (ACOG, 2002a). Betamethasone is also recommended, 12 mg intramuscularly every 24 hours for two doses to accelerate fetal lung maturity in patients between 24 and 34 weeks of gestation (Liggins and Howie, 1972).

If a diagnosis of preterm labor is made and contractions do not subside with bed rest and hydration, pharmacologic therapy is considered. Contraindications to stopping labor include chorioamnionitis, abruptio placentae, heavy vaginal bleeding, severe or chronic hypertension, and fetal demise. Although many tocolytic drugs are available, terbutaline and magnesium sulfate are used often.

Terbutaline at 0.25 mg can be administered subcutane-ously every 20 to 30 minutes for three doses. If this is successful, oral therapy can be instituted at doses of 2.5 to 5.0 mg every 2 to 6 hours. Doses should be individualized, allowing maximal efficacy and low side effects. Through beta-1 receptors, beta agonists increase heart rate and thus stroke volume, increase fat breakdown, drive intravascular potassium into cells, and decrease gastrointestinal motility. Through beta-2 receptors, bronchial and uterine smooth muscle relaxation and glycogenolysis occurs. Certain maternal cardiac disorders are a contraindication to this therapy. Women taking beta-adrenergic agonists experience tachycardia, jitteriness, and occasionally nausea and vomiting. Maternal heart rate of 120 beats/min or greater is a contraindication for further dosing, and the interval or quantity may need modification. Fetal heart rate elevations can also be seen.

Intravenous magnesium sulfate therapy can also be used for preterm labor. There is no clear-cut greater efficacy of one tocolytic versus another. Magnesium sulfate relaxes uterine smooth muscle by competitive inhibition of the action of calcium. The dose should be adjusted so that contractions are decreased or abolished but maternal toxicity is not reached. This can be done by frequent examination of deep tendon reflexes, which should be present but depressed. Complete loss of deep tendon reflexes can herald further toxicity, and dosing should be decreased. Plasma magnesium levels can also be performed and should be kept between 5 and 8 mg/dL. Because it is excreted predominantly by the kidney, the plasma magnesium level is influenced by urine output as

EVIDENCE-BASED SUMMARY

• There are no clear "first-line" tocolytic drugs to manage preterm labor; clinical circumstances and physician preferences should dictate treatment (SOR: A).

• Antibiotics do not appear to prolong gestation and should be reserved for group B streptococcal prophylaxis in patients in whom delivery is imminent (SOR: A).

• Neither maintenance treatment with tocolytic drugs nor repeated acute tocolysis improves perinatal outcome; neither should be undertaken as a general practice (SOR: A).

• Tocolytic drugs may prolong pregnancy for 2 to 7 days, which may allow for administration of steroids to improve fetal lung maturity and consideration of maternal transport to a tertiary care facility (SOR: A).

• Cervical ultrasound examination and fetal fibronectin testing have good negative predictive value; thus, either approach or both combined may be helpful in determining which patients do not need tocolysis (SOR: B).

• Amniocentesis may be used in women in preterm labor to assess fetal lung maturity and intra-amniotic infection (SOR: B).

• Bed rest, hydration, and pelvic rest do not appear to improve the rate of preterm birth and should not be routinely recommended (SOR: B).

Data from ACOG, 2003.

well as infusion rate. Calcium gluconate should be readily available in case of magnesium toxicity. Women receiving IV magnesium experience warmth, flushing, and poor muscle tone; some develop diplopia, nausea, and vomiting. The majority of these side effects occur with the loading dose. Magnesium sulfate therapy is typically used for 24 hours, then discontinued. Long-term tocolytic therapy has not been shown to be efficacious.

Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

Get My Free Ebook


Post a comment