Administration of Antenatal Corticosteroids: Optimal Timing

The effectiveness of antenatal corticosteroids (ACS) in significantly reducing respiratory distress syndrome (RDS) depends crucially on the timing. It is successful if delivery takes place between 24 hours and seven days following administration; after this period, the side effects seem to predominate. In addition, an increased rate of mental impairment and behavioral disorders are observed in children born full-term after ACS administration. The optimal timing of ACS administration depends crucially on the given indication; to date, it has been achieved in only 25-40% of cases. ACS administration is always indicated in PPROM, in severe early pre-eclampsia, in fetal IUGR with zero or reverse flow in the umbilical artery, in placenta previa with bleeding, and in patients experiencing premature labor with a cervical length < 15 mm. The risk of women with asymptomatic cervical insufficiency giving birth within seven days is very low. In this case, ACS should not be administered even if the patient's cervical length is less than 15 mm, provided that the cervix is closed and there are no other risk factors for a premature birth. The development of further diagnostic methods with improved power to predict premature birth is urgently needed in order to optimize the timing of ACS administration in this patient population. Caution when administering ACS is also indicated in women experiencing premature labor who have a cervical length >= 15 mm. Further studies using amniocentesis are needed in order to identify the patient population with microbial invasion of the amniotic cavity/intra-amniotic infection (MIAC/IAI), and to define threshold values at which delivery is indicated. ACS administration is not performed as an emergency measure, usually not even before transfer to a perinatal center. Therefore, whenever possible, the indication for ACS administration should be determined by a clinician who is highly experienced in perinatology.