Labor and Delivery Preterm Labor

Tocolytic Therapy

• Preterm labor is labor that occurs between 20 and 37 weeks of gestation.

Tocolytic Therapy

• The goals of tocolytic therapy are to postpone delivery long enough to allow for maximum effect of antenatal steroids, for transportation of the mother to a facility equipped to deal with high-risk deliveries, and to prolong pregnancy when there are underlying self-limited conditions that can cause labor. Tocolytics can be started when there are regular uterine contractions with cervical change. Do not use them in cases of intrauterine fetal demise, a lethal fetal anomaly, intrauterine infection, fetal distress, severe preeclampsia, vaginal bleeding, or maternal hemodynamic instability.
• There are four classes of tocolytics: β-agonists (terbutaline and ritodrine [not available in the United States], magnesium sulfate, NSAIDs, and calcium channel blockers. Prolongation of pregnancy with tocolytics is not associated with significant reduction in rates of respiratory distress syndrome or neonatal death.
• β-Agonists have a higher risk for maternal side effects. Terbutaline doses range from 250 to 500 mcg subcutaneously every 3 to 4 hours. The FDA cautions that injectable terbutaline should not be used to prevent preterm labor or treat it beyond 48 to 72 hours because of the risk for maternal death and heart problems, including cardiac arrhythmias, myocardial infarction, pulmonary edema, and tachycardia. Do not use terbutaline outside of the hospital. Do not use oral terbutaline for the prevention or treatment of preterm labor, as it has the same risks as the injectable form but has not been shown to be effective.
• A Cochrane review does not support the effectiveness of magnesium sulfate.
• Nifedipine is associated with fewer side effects than magnesium or β-agonists. Five to 10 mg nifedipine may be administered sublingually every 15 to 20 minutes for three doses. Once stabilized, 10 to 20 mg may be administered orally every 4 to 6 hours for preterm contractions. It can cause hypotension and a change in uteroplacental blood flow.
• Indomethacin, 50 to 100 mg orally or rectally, followed by 25 to 50 mg orally every 6 hours has been used. Premature constriction of the ductus arteriosus has been reported.

Antenatal Glucocorticoids

• A Cochrane review shows the benefit of antenatal corticosteroids for fetal lung maturation to prevent respiratory distress syndrome, intraventricular hemorrhage, and death in infants delivered prematurely.
• Current recommendations are betamethasone, 12 mg IM every 24 hours for two doses, or dexamethasone, 6 mg IM every 12 hours for four doses, to pregnant women between 26- and 34-weeks’ gestation who are at risk for preterm delivery within the next 7 days. Benefits from antenatal glucocorticoid administration are believed to begin within 24 hours.

Cervical Ripening and Labor Induction

• Prostaglandin E2 analogues (eg, dinoprostone [Prepidil gel and Cervidil vaginal insert]) are commonly used for cervical ripening. Fetal heart rate monitoring is required when Cervidil is used. Misoprostol, a prostaglandin E1 analogue, is effective and inexpensive, but it has been associated with uterine rupture.
• Oxytocin is the most commonly used agent for labor induction after cervical ripening.

Labor Analgesia

• The IV or IM administration of narcotics is commonly used for pain associated with labor. Compared with epidural analgesia, parenteral opioids are associated with lower rates of oxytocin augmentation, shorter stages of labor, and fewer instrumental deliveries.
• Epidural analgesia involves administering an opioid and/or an anesthetic (eg, fentanyl and/or bupivacaine) through a catheter into the epidural space to provide pain relief. Epidural analgesia is associated with longer stages of labor, more instrumental deliveries, and maternal fever compared to parenteral narcotic analgesia. Patientcontrolled epidural analgesia results in a lower total dose of local anesthetic. Complications of epidural analgesia include hypotension, nausea, vomiting, itching, and urinary retention.
• Other options for labor analgesia include spinal analgesia and nerve blocks.

Lactation Issues Drug Use During Lactation

• Medications enter breast milk via passive diffusion of nonionized and non–protein bound medication. Drugs with high molecular weights, lower lipid solubility, and higher protein binding are less likely to cross into breast milk, or they transfer more slowly or in smaller amounts. The higher the maternal serum concentration of drug, the higher the concentration will be in breast milk. Drugs with longer half-lives are more likely to maintain higher levels in breast milk. The timing and frequency of feedings and the amount of milk ingested by the infant are also important.
• Strategies for reducing infant risk from drugs transferred into breast milk include selecting medications for the mother that would be considered safe for use in the infant and choosing medications with shorter half-lives, higher protein binding, lower bioavailability, and lower lipid solubility.

RELACTATION

For relactation use metoclopramide, 10 mg three times daily for 7 to 14 days only if nondrug therapy is ineffective.