Version July 2025
ACS: antenatal corticosteroids; bpm: beats per minute; GA: gestational age; IV: intravenous; SubQ: subcutaneous.
* Tocolytic choices are different at ≥32 weeks of gestation (eg, indomethacin is not used).
¶ There is no standard for indomethacin dosing. We use 50 to 100 mg loading dose (usually orally, but may be given rectally), which is a common loading dose, followed by 25 mg orally every 4 to 6 hours (maximum daily dose 200 mg), which is the usual maintenance dose. We do not use indomethacin for more than 72 hours because of concern about premature constriction of the ductus arteriosus and oligohydramnios. We perform ultrasound and fetal echocardiography to monitor amniotic fluid volume and ductal effects if the duration of therapy exceeds 48 hours, which is rare. However, fetal echocardiography may be delayed if not available on the labor unit and the duration of tocolysis has not exceeded 72 hours. Gestational age is also a consideration. For example, some clinicians do not administer indomethacin after 28 or 30 weeks or use lower doses after 28 or 30 weeks; and some use higher doses at 22 to 25 weeks (eg, 100 mg loading dose followed by 50 mg every 4 to 6 hours). Peak maternal plasma levels are achieved within 2 hours after dosing with a half-life of approximately 4.5 hours[1].
For patients who have contraindications to indomethacin use or do not tolerate it because of side effects, we use immediate-release nifedipine.
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 immediate-release nifedipine dosing. We use 20 to 30 mg orally 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 maternal plasma levels are achieved in 45 to 60 minutes with a half-life of 2 to 3 hours[2].
For patients already on nifedipine because of contraindications/intolerance to indomethacin, we would add terbutaline. 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 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 until 48 hours after administration of the 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.