AJOG states:3

“The failure to accurately predict impending preterm delivery was apparent from the Liggins and Howie study, in which approximately 1 in 3 women delivered >7 days after ACS administration. We have known for >50 years that timing is everything in regard to ACS efficacy, but the precision in our administration timing has not improved.
By 2019, only 15% to 40% of women treated with ACS were treated within the optimal window of 7 days before delivery, leading to an approximate 50% reduction in expected benefit, irrespective of confounders. It has been estimated that for every 3 to 4 cases of premature births in which ACS were administered >7 days before delivery, the associated increase in neonatal mortality (when compared with those cases in which ACS administration was optimally timed) is roughly equivalent to the neonatal mortality associated with 1 case of failure to administer ACS.”