By 34 weeks fetal lungs are usually matured we dont get good results and we also dont use after 37because lungs became alreadt mature. Given medicine to speed up lung development, which takes at least 48 hours to fully benefit the baby's lungs.
Even 24 hours provides some benefit. If a baby is at risk of being born too early, giving the mother steroids before the birth can help her unborn baby's lungs to develop more quickly. Betamethasone and dexamethasone cause an immature fetus's lungs to produce a compound called surfactant.
A full-term baby's lungs. Consider having steroids to mature the baby's lungs at 24 weeks just steroids (usually 2 doses) either betamethasone or dexamethasone.