Betamethasone is a synthetic corticosteroid administered to pregnant patients at risk of premature delivery. The drug crosses the placenta and accelerates fetal lung development. It works by stimulating the production of surfactant, a substance lining the air sacs necessary to prevent lung collapse after birth. A single course significantly reduces the risk of neonatal mortality, respiratory distress syndrome, and other complications of prematurity, such as bleeding in the brain and serious intestinal infections. Healthcare providers administer this therapy after assessing the risk of preterm birth versus the potential benefits for the fetus.
Medical Indications for Treatment
The primary purpose of administering betamethasone is to prepare the fetus when delivery is expected significantly before term. This intervention is considered when a patient faces a high risk of giving birth within the next seven days. This risk often arises from spontaneous events like threatened preterm labor, characterized by regular contractions and cervical changes.
Another common indication is the premature rupture of membranes (PPROM), where the amniotic sac breaks before labor begins. Betamethasone is also administered when a planned preterm delivery is necessary for maternal or fetal health. These medically indicated deliveries might be due to conditions such as severe preeclampsia, fetal growth restriction, or certain placental issues.
The treatment is warranted only if the risk of an early birth is high, ensuring the fetus receives the full benefit before delivery. It is not typically given if the likelihood of delivery is low or if the patient is already at term.
Critical Timing Based on Gestational Age
The effectiveness of betamethasone depends strongly on the fetus’s gestational age at administration. The therapeutic window is generally between 24 weeks 0 days and 33 weeks 6 days for women at risk of preterm birth within a week. This period is optimal because the lungs are immature enough to benefit greatly from the steroid, yet the fetus is viable.
For pregnancies in the periviable period (22 weeks 0 days to 23 weeks 6 days), administration requires careful discussion. Treatment in this range is considered only after detailed counseling with the parents and the neonatal team, accounting for local viability limits and parental wishes. Guidelines recommend a single course of treatment throughout this early-preterm period.
Guidelines have recently broadened to consider a single course for singleton pregnancies between 34 weeks 0 days and 36 weeks 6 days gestation. This late-preterm administration is reserved for patients who have not received prior treatment and remain at high risk of delivery within seven days. The greatest reduction in severe respiratory complications, however, is seen in the earlier gestational ages. The medication works best when delivery occurs between 24 hours and seven days after the first injection, often called the “rescue dose” window.
Administration Protocol and Dosing Schedule
The standard protocol involves two separate 12-milligram doses given intramuscularly, with the second dose administered 24 hours after the first. This regimen ensures the medication is slowly released into the mother’s bloodstream, allowing it to cross the placenta and reach the fetal circulation effectively.
Betamethasone is a mixture of fast-acting (phosphate) and slow-releasing (acetate) forms, contributing to its sustained therapeutic effect. The full course provides maximum benefit to the fetal lungs, achieved within the week following the injection. Healthcare providers monitor the patient closely, attempting to delay delivery until this maturation effect occurs.
A second or “repeat” course is not recommended for routine use due to concerns about fetal growth and development. However, a single repeat course may be considered if the patient remains at high risk of preterm birth within seven days, is less than 34 weeks gestation, and the initial course was administered more than 7 to 14 days prior.
Short-Term Maternal and Neonatal Considerations
Betamethasone administration has predictable short-term effects on both the mother and the fetus that require monitoring. For the mother, the most common transient effect is a temporary elevation in blood glucose levels, a known effect of corticosteroids. This is concerning for patients with pre-existing or gestational diabetes, who may require a temporary increase in insulin dosage to maintain safe blood sugar control.
For the fetus, the medication induces transient changes in biophysical activity. These effects include a temporary decrease in fetal heart rate variability and a reduction in fetal body and breathing movements, typically observed within 48 to 72 hours after the first injection. Healthcare providers interpret fetal monitoring findings with caution during this expected suppression. The changes are a temporary pharmacological effect and usually resolve within 96 hours.