MANAGEMENT OF PRETERM LABOR
The purpose in treating preterm labor is to delay delivery, if possible, until fetal maturity is attained.
Management involves two broad goals: (1) the detection and treatment of disorders associated with preterm labor, and (2) therapy for the preterm labor itself. Fortunately,more than 50% of patients with preterm contractions have spontaneous resolution of abnormal uterine activity. However,this complicates the evaluation of effectiveness of specific treatments, because it is unclear if the contractions would have resolved spontaneously or if their cessation was due to effective treatments.
Various tocolytic therapies have been used in the management of preterm labor (Table 20.1). Tocolytics have not been shown to prolong pregnancy beyond sev-eral days (only 2 to 7). Different treatment regimens ad-dress specific mechanisms involved in the maintenance of uterine contractions, and each, therefore, may be best suited for certain patients.
Typically, patients with a diagnosis of preterm labor receive one form of tocolytic therapy, with the addition or substitu-tion of other medications if the initial treatment is considered unsuccessful.
Magnesium sulfate has been the most frequently used agent, but use of nifedipine is increasing. Evidence as to ef-ficacy beyond several days is weak, but often management allows for administration of corticosteroid therapy. Adverse side effects, at times serious and even life-threatening to the mother, can occur. The gestational age of the fetus is always a consideration in deciding how vigorously to pur-sue therapy. For example, maternal risks may be more ac-ceptable when treating a 26-week fetus as compared to a 32-week fetus.
Contraindications to tocolysis include conditions in which the adverse effects of tocolysis may be significant, such as advanced labor, a mature fetus, a severely anom-alous fetus (from lethal congenital or chromosomal abnormalities), intrauterine infection, significant vaginal bleed-ing, and severe preeclampsia.
In addition, a variety of obstetric complications, such as placental abruption, ad-vanced cervical dilatation, or evidence of fetal compro-mise or placental insufficiency, may contraindicate delay in delivery.
From 24 to 32 to 34 weeks of gestation, management generally includes administration of corticosteroids (be-tamethasone or dexamethasone) to enhance fetal pul-monary maturity. A single course of corticosteroids should begiven to pregnant women between 24 and 32 weeks of gestation who are at risk of preterm delivery. Both the incidence andseverity of fetal respiratory distress syndrome are reduced with such therapy. Between 32 and 34 weeks of gestation,the use of steroids to enhance fetal lung maturity is less certain. In addition, other sequelae of prematurity, such as interventricular hemorrhage and necrotizing enterocoli-tis, occur less frequently in infants whose mothers re-ceived corticosteroid therapy. Maximal benefit to the fetus occurs if the therapy is administered within 7 days of de-livery; however, routine weekly courses are not recom-mended because of potential negative fetal effects.
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