19.10 Preterm Labor

Common Medications Used in Preterm Labor^[7]

Indomethacin

• Mechanism of Action: Indomethacin is a cyclooxygenase inhibitor (COX inhibitor) and nonsteroidal anti-inflammatory drug (NSAID) that inhibits prostaglandins released during labor. Prostaglandins soften the cervix and relax the cervical muscles, which helps the cervix dilate. They also increase intracellular calcium levels, which causes the myometrial muscle to contract and move the fetus through the maternal pelvis. Indomethacin helps stop these physiological actions of labor.
• Indications: Indomethacin is used for preterm labor in pregnancies less than 32 weeks’ gestation for up to 48 hours to allow administration of ACS. Duration of therapy is typically not greater than 48 hours due to the potential adverse effects.
• Contraindications: Indomethacin is contraindicated in maternal thrombocytopenia, kidney dysfunction, gastrointestinal bleeding, or in pregnancies greater than 32 weeks’ gestation due to risk of premature closure of the fetal ductus arteriosus.
• Adverse Effects: Adverse effects include gastrointestinal upset (nausea, vomiting, reflux, abdominal pain), thrombocytopenia, oligohydramnios, renal dysfunction, and hypertension. Neonatal adverse effects include risk of premature closure of the fetal ductus arteriosus in gestations less than 32 weeks, chronic lung disease, and intraventricular hemorrhage.

Nifedipine

• Mechanism of Action: Nifedipine is a calcium channel blocker that blocks calcium ions from entering the uterine muscle cell membrane, ultimately resulting in uterine wall relaxation. It also causes peripheral vasodilation.
• Contraindications: Nifedipine is contraindicated with maternal hypotension, heart failure, and liver dysfunction.
• Adverse Effects: Maternal adverse effects are related to associated peripheral vasodilation and may include flushing, hypotension, dizziness, headache, peripheral edema, headache, and nausea. There are no reported fetal adverse effects with oral doses of nifedipine commonly used for labоr inhibition.

Terbutaline

• Mechanism of Action: Terbutaline selectively stimulates beta-2 adrenergic receptors and relaxes smooth muscle, thus reducing or stopping uterine contractions. It is not approved for prolonged tocolysis greater than 48 to 72 hours.
• Contraindications: Terbutaline is contraindicated with ischemic heart disease, hypertension, arrhythmias, diabetes mellitus, seizure disorders, hyperthyroidism, and tachycardia greater than 120 beats per minute.
• Adverse Effects: Many of the maternal side effects are related to stimulation of beta-1 adrenergic receptors that increase maternal heart rate and stroke volume, as well as stimulation of beta-2-adrenergic receptors that cause peripheral vasodilation, diastolic hypotension, and bronchial relaxation. The combination of these two cardiovascular effects leads to tachycardia, palpitations, and hypotension. Beta-agonists also cause hyperglycemia and hypokalemia. Beta-agonists cross the placenta and can cause fetal tachycardia and neonatal hypoglycemia. Terbutaline has a boxed warning against prolonged use for more than 48 to 72 hours related to these maternal cardiac adverse effects and risk of maternal death.

Magnesium Sulfate

Magnesium sulfate may be used in some settings to delay preterm labor, although it is not FDA approved for this purpose due to its potential adverse effects, including magnesium toxicity. Magnesium sulfate is also prescribed to prevent or treat seizures (eclampsia) in clients with preeclampsia.

• Mechanism of Action: Magnesium sulfate is thought to inhibit calcium transport in the uterine muscle cells, thus reducing the intensity and frequency of uterine contractions. It also has a neuroprotective effect in the very premature fetus (i.e., <32 weeks of gestation). ACOG considers magnesium sulfate an option for short-term prolongation of рrеgոaոсy (up to 48 hours) to allow administration of ACЅ.^[8]
• Contraindications: Magnesium sulfate should not be administered to mothers with myasthenia gravis or known cardiac conduction disorders due to its anti-inotropic effects. Dosage modifications are required for clients with kidney impairment.
• Adverse effects: Adverse effects are related to magnesium toxicity (i.e., hypermagnesemia). Deep tendon reflexes, respiratory rate, and urine output must be closely monitored. Loss of patellar deep tendon reflex is the first manifestation of symptomatic hypermagnesemia. Dosage should be withheld if respirations are less than 12 breaths per minute or if urine output is less than 100 mL per four hours (or at least 0.5 mLs/kg/hour).

Antenatal Corticosteroids (ACS) 

Examples of antenatal corticosteroids (ACS) are betamethasone or dexamethasone.

• Mechanism of Action: ACS induce fetal pulmonary beta-receptors, resulting in ѕսrfаctaոt release and absorption of alveolar fluid. However, for these changes to occur, the fetal lungs must reach a developmental stage that is biologically responsive to ϲοrtiϲοѕterοidѕ.
• Indications: ΑCЅ is generally administered during pregnancies of 22 weeks to 33 weeks +6 days’ gestation for whom delivery within the next seven days is anticipated. Pregnancies less than 22 weeks gestation are not considered candidates for AСS because there are only a few primitive alveoli at this gestational age on which the drug can exert an effect.
• Adverse Effects: ACS are associated with transient fetal heart rate changes and decreased variability, as well as increased risk for neonatal hypoglycemia and severe infection. ACS may also affect long-term neurodevelopmental outcomes.

Nursing Assessments and Interventions For Preterm Labor

• Assess maternal and fetal status
  • Monitor maternal blood pressure, heart rate, respiratory rate, and temperature.
  • Assess continuous electronic fetal monitoring for frequency, duration, and intensity of uterine contractions and fetal heart rate patterns for fetal well-being.
  • Assess the client’s pain level and provide pain relief measures.
• Implement interventions to delay labor
  • Assist the client to comfortable positions and encourage rest to minimize physical activity. However, bed rest is not recommended due to the risk of thrombosis.
  • Provide a calm, safe, and supportive environment.
  • Administer prescribed tocolytic medications (such as indomethacin, nifedipine, terbutaline, and magnesium sulfate). Evaluate effectiveness of medications, as well as monitor for adverse effects.
  • Encourage oral fluids to prevent dehydration, which can trigger contractions.
• Administer prescribed antenatal corticosteroids to accelerate fetal lung maturation.
• Provide nutritional guidance to ensure the client’s dietary needs are met.
• Provide emotional support
  • Address the client’s concerns and feelings of anxiety.
  • Encourage the client and her partner to express their feelings and communicate their needs.
• Provide health teaching about preterm labor, the purpose and side effects of prescribed medications, and the importance of adhering to bed rest and activity restrictions.
• Collaborate with the multidisciplinary health care team to ensure coordinated care. Promptly communicate changes in fetal monitoring or the client’s condition to the health care provider.
• Maintain thorough documentation of assessments, interventions, and evaluation of effectiveness.