
Antenatal Corticosteroids (ACS) — A Practical Guide
Any woman at risk of preterm birth within the next 7 days — from preterm labor, PPROM, or a planned preterm delivery for a maternal or fetal indication
Betamethasone: 12 mg IM, two doses, 24 hours apart
Dexamethasone: 6 mg IM, four doses, 12 hours apart
Either drug is acceptable — choice usually comes down to local availability and protocol, not a meaningful difference in benefit
Betamethasone and dexamethasone cross the placenta and bind glucocorticoid receptors in fetal tissue, switching on genes that drive structural maturation
In the lungs: accelerates maturation of type II pneumocytes and boosts surfactant production — surfactant lowers surface tension in the air sacs, keeping them open after birth
Also thins the air–blood barrier and increases lung compliance, so the newborn lung is mechanically ready to breathe air effectively
Beyond the lungs: stabilizes fragile blood vessels in the brain's germinal matrix (lowering IVH risk) and matures the gut lining (lowering NEC risk)
Consider one rescue course if the prior course was given more than 7–14 days ago (per local protocol), the pregnancy is still under 34 weeks, and preterm birth is now likely again within 7 days
Avoid multiple repeat courses — repeated exposure has been linked to lower birth weight and raises theoretical concerns about neurodevelopment
PPROM is one of the most common reasons ACS is given — ruptured membranes themselves don't change the dose or drug choice
Give a course promptly on diagnosis if the pregnancy is under the usual gestational cut-off, since the time to delivery after PPROM is often unpredictable
ACS does not meaningfully increase maternal or neonatal infection rates in PPROM — this has been consistently shown across trials, and the lung benefit for the baby outweighs the theoretical infection concern
Best paired with latency antibiotics per local protocol — steroids and antibiotics are complementary decisions here, not competing ones
If the pregnancy continues well past the 7-day benefit window without delivery, and preterm birth risk re-emerges, a single rescue course can be considered — same criteria as above
Reduces respiratory distress syndrome (RDS) and the need for respiratory support
Reduces intraventricular haemorrhage (IVH), necrotizing enterocolitis (NEC), and neonatal death
Benefit is strongest from 24–34 weeks; in the late preterm window (34–36+6 weeks) the effect is more modest but still real — mainly less transient respiratory distress
Transient hyperglycaemia — peaks 12–24 hours after a dose and can last several days; matters most in diabetic mothers
Transient leukocytosis (raised white cell count) — can mimic or mask signs of infection on blood tests
Mild, usually clinically insignificant rise in blood pressure
Rare — pulmonary oedema: risk rises when steroids are combined with tocolytics and generous IV fluids; watch fluid balance closely
Transiently reduced fetal movements and heart rate variability for 48–96 hours — an expected response, not a sign of compromise
Neonatal hypoglycaemia — from rebound after the maternal glucose effect wears off
With repeated courses: lower birth weight, and theoretical neurodevelopmental concerns (see Repeat Course above)
Steroids transiently raise maternal blood glucose
Anticipate closer glucose monitoring, and possible insulin adjustment, for 3–5 days
Not an absolute contraindication
Weigh infection risk individually, with senior input
Same maternal dose regardless of the number of fetuses
Indication and timing principles are unchanged
Only if no prior course was given
Smaller absolute benefit — still worth giving if birth is likely within 7 days
24 Hours to 7 Days
TO BEST-TIMED DELIVERY
Even a single dose shortly before birth has some benefit — don't withhold it because delivery seems imminent
If delivery ends up more than 7 days away, reconsider a single rescue course closer to the time, if still preterm
Never delay a medically necessary urgent delivery solely to finish the steroid course
Document the timing of each dose clearly — it shapes what the neonatal team expects and plans for
