In general, tocolytics are not indicated for use before
neonatal viability. Regardless of interventions, perinatal
morbidity and mortality at that time are too high to justify
the maternal risks associated with tocolytic therapy.
Similarly, no data exist regarding the efficacy of corticosteroid
use before viability. However, there may be times
when it is appropriate to administer tocolytics before
viability. For example, inhibiting contractions in a patient
after an event known to cause preterm labor, such as
intra-abdominal surgery, may be reasonable even at previable
gestational ages, although the efficacy of such an
intervention remains unproved (31, 32). The upper limit
for the use of tocolytic agents to prevent preterm birth
generally has been 34 weeks of gestation. Because of the
possible risks associated with tocolytic and steroid therapies,
the use of these drugs should be limited to women
with preterm labor at high risk of spontaneous preterm
birth. Tocolysis is contraindicated when the maternal and
fetal risks of prolonging pregnancy or the risks associated
with these drugs are greater than the risks associated with
preterm birth (see Box 1).