Version July 2025
ACS: antenatal corticosteroids; bpm: beats per minute; IV: intravenous; SubQ: subcutaneous.
* 34 weeks of gestation is the threshold at which many experts believe that perinatal morbidity and mortality are sufficiently low that the potential maternal side effects, pregnancy complications, and costs associated with inhibition of preterm labor and short-term delay of delivery are not justified. Choice of tocolytic is different before 32 weeks.
¶ There is no standard for immediate-release nifedipine dosing. We use 20 to 30 mg orally (immediate-release) initial loading dose, followed by an additional 10 to 20 mg orally every 3 to 8 hours for up to 48 hours (maximum dose 180 mg/day), but other doses and formulations are used. For example, an initial dose of 40 mg orally administered in divided doses every 10 to 20 minutes over one hour is a common alternative. After oral administration, peak plasma levels are achieved in 45 to 60 minutes with a half-life of 2 to 3 hours.[1]
For patients who have contraindications to nifedipine use or do not tolerate it because of side effects, we use terbutaline.
Δ A course of ACS consists of betamethasone 2 doses of 12 mg intramuscularly 24 hours apart or dexamethasone 4 doses of 6 mg intramuscularly 12 hours apart.
◊ The point of futility is a clinical judgment, but can be considered when persistent contractions result in substantial labor progression (eg, cephalic presentation with cervix 6 cm dilated and intact membranes but sooner if noncephalic presentation or membranes spontaneously rupture).
§ There is no standard for terbutaline dosing. It is often given SubQ. We use 0.25 mg SubQ every 20 to 30 minutes for up to 4 doses or until tocolysis is achieved, whichever occurs first. Once labor is inhibited, we give 0.25 mg SubQ every 3 to 4 hours until 48 hours after administration of the first ACS dose. Terbutaline can also be administered as a continuous IV infusion, starting at 2.5 to 5 mcg/min and increasing by 2.5 to 5 mcg/min every 20 to 30 minutes to a maximum of 25 mcg/min, or until the contractions have abated. At this point, the infusion is reduced by decrements of 2.5 to 5 mcg/min every 30 to 60 minutes to the lowest dose that maintains uterine quiescence for 48 hours after administration of the first ACS dose. Terbutaline (SubQ or IV) is held if the maternal heart rate exceeds 120 bpm; glucose and potassium are monitored every 4 to 6 hours.