Thorp, John M., Jr. (2011). Examining the Evidence: What Is the Optimal Interval between Administration of Antenatal Corticosteroids and Preterm Delivery?. OBG Management, 23(11)
No more than 7 days, according to this retrospective review of 254 preterm (<34 weeks) births. Infants delivered more than 7 days after administration of antenatal corticosteroids had a higher risk of intubation for respiratory morbidity.
Thorp, John M., Jr.