Preterm labour (PTL)

Preterm Labor (PTL)

 

Management

Two Goals: Reduce uterine activity, optimize fetal status.

Bed rest: No trials have shown benefit.

Hydration: In theory, hydration should reduce contractility through the Henry-Gauer reflex, inhibiting the release of ADH. Studies have shown no benefit, and no reduction in preterm delivery. May actually be harmful and lead to fluid overload if a fluid bolus is given and then the patient is started on magnesium.

Sedation: Studies have shown no benefit, and no reduction in preterm delivery.

Progesterone: Six studies have shown that 17a-hydroxy-progesterone caproate prevents preterm delivery with an odds ration of 0.5, but there is no benefit in treating active labor.

Tocolytics: The use of tocolytics have shown no reduction in preterm delivery, but only a delay in delivery of about 24-48 hours. Therefore, the goal of tocolytic therapy should be to provide time to administer steroids to optimize fetal outcome, and it is therefore limited to 48 hours use before 34 weeks.

b-Sympathomimetic agents result in uterine smooth muscle relaxation by activation of b₂ receptors (also found in blood vessels, bronchioles, and liver). Studies have shown no reduction in preterm birth with Terbutaline, but a delay in delivery of 24-48 hours has been demonstrated. The initial infusion is 5–10 mg per minute, increased when necessary every 10–15 minutes to a maximum of 80 mg per minute. Terbutaline may be administered subcutaneously in 0.25-mg doses every 20–30 minutes (four to six doses). Relative contraindications to use include diabetes mellitus, underlying cardiac disease, use of digitalis, hyperthyroidism, severe anemia, and hypertension. Side effects include cardiac arrythmias, pulmonary edema, and myocardial ischemia.

Magnesium sulfate is calcium antagonist. It is usually administered intravenously as an initial bolus of 4–6 g over 30 minutes, followed by a maintenance infusion of 1–3 g per hour. Serum magnesium levels of 5–8 mg/dL are considered therapeutic for inhibiting myometrial activity. Common side effects noted with the use of magnesium sulfate include flushing, nausea, headache, drowsiness, and blurry vision. Diminishment of deep tendon reflexes occurs when serum magnesium levels exceed 12 mg/dL. Significant respiratory depression can occur as serumlevels reach 14–18 mg/dL, and cardiac arrest may occur with levels greater than 18 mg/dL. Absolute contraindications to the use of magnesium ulfate include myasthenia gravis and heart block. Relative contraindications include underlying renal disease and recent myocardial infarction. Concurrent use of calcium channel blockers and magnesium sulfate can theoretically result in profound hypotension. It is felt that Magnesium sulfate has the most favorable side-effect profile of the currently used tocolytics and therefore should be first-line therapy.

Inomethacin is a prostaglandin synthetase inhibitor. Indomethacin is usually administered orally or rectally. A loading dose of 50–100 mg is followed by a total 24-hour dose not greater than 200 mg. Indomethacin blood concentrations usually peak 1 to 2 hours after oral administration, whereas rectal administration is associated with levels that peak slightly sooner. Usage longer than 48 hours may lead to oligohydramnios or premature PDA closure. It should be not be used past 30-32 weeks gestation because of these concerns and an increased risk for necrotizing enterocolitis. It may be added as a second-line agent to patients who have failed Magnesium.

Calcium channel blockers decrease uterine contractility and uterine pacemaker activity. Studies have shown Nifedipine (Procardia) to be as effective as magnesium in delaying delivery by 24-48 hours. Maintenance nifedipine has shown no benefit in preventing preterm delivery. An initial loading dose of 20 mg orally is typically given, followed by 10–20 mg every 6–8 hours. Contraindications to the use of calcium channel blockers include hypotension, congestive heart failure, and aortic stenosis.

Antibiotics: No large studies have yet shown benefit for antibiotics reducing preterm delivery. However, antibiotics may be indicated for Group B streptococcus prophylaxis in all women who are in preterm labor and who do not have a negative screen.

 IV penicillin G (5 mU initially and then 2.5 mU every 4 hours) until delivery is recommended or 

IV ampicillin(2 g initially and then 1 g every 4  hours until delivery).

Corticosteroids: All women at risk for preterm delivery between 24-34 weeks should be administered betamethasone (12 mg intramuscularly every 24 hours, two doses) or if unavailable dexamethasone (6 mg intramuscularly every 12 hours, four doses). Administration significantly reduce the risk of respiratory distress syndrome, intraventricular hemorrhage, and neonatal death. Maximum neonatal benefit is between 24 hours and seven days after administration. Repeated courses are not currently recommended.