Antenatal steroids, also known as antenatal corticosteroids, are medications administered to pregnant women expecting a preterm birth. When administered, these steroids accelerate the maturation of the fetus' lungs, which reduces the likelihood of infant respiratory distress syndrome and infant mortality. The effectiveness of this corticosteroid treatment on humans was first demonstrated in 1972 by Sir Graham Liggins and Ross Howie, during a randomized control trial using betamethasone.
Uses
Preterm birth
Antenatal steroids have been shown to reduce the occurrence and mortality of infant respiratory distress syndrome, a life-threatening condition caused by underdeveloped lungs.
Current evidence suggests that giving antenatal corticosteroids reduces risk of late miscarriages and baby deaths. The baby is also less likely to develop respiratory distress syndrome or die during or after birth. They are also less likely to have intraventricular hemorrhage (bleeding of the brain), necrotizing enterocolitis (problems with the bowels), or systemic infections (infections affecting the whole body) in the first two days of life.
Steroids do not appear to increase the number of women who develop infection of the fetal membranes (chorioamnionitis) or of the womb (endometritis).
There is robust evidence that a single course of antenatal corticosteroids (i.e., 24 mg of betamethasone or dexamethasone), when there is a risk of preterm birth (at less than 34 weeks of gestation), reduces the risk of child death, regardless of resource level.
Multiple gestation
Further research must be conducted to adequately determine outcomes of antenatal steroid administration for multiple pregnancies. However, certain national clinical practice guidelines recommend the usage of steroids for preterm birth regardless of multiple gestation.
Preterm premature rupture of membranes
Antenatal steroids have also been shown to have definite beneficial effect in treating the condition of preterm premature rupture of membranes (PPROM). Similar to its effects on preterm birth, research evidence suggests that the administration of antenatal steroids to patients with PPROM reduces risks of neonatal mortality, intraventricular hemorrhage and respiratory distress syndrome.
Adverse effects
Preliminary research has suggested that the use of antenatal corticosteroids may have adverse long-term effects. In animals, antenatal corticosteroid use has been associated with adverse effects on the cardiometabolic system and inhibited growth of the brain, as well as worsened memory and learning difficulties. While it is not yet certain if human fetuses would experience these same effects, some literature has found that human preterm fetuses treated with antenatal corticosteroids may be at greater risk of developing mental and behavioural disorders during childhood, as these drugs are able to enter the fetus' brain and could affect neurodevelopment. In both humans and animals, research has suggested that repeated doses of antenatal corticosteroids could lead to an increased risk of vision and hearing issues in the long-term.
Contraindications
Contraindications to the administration of antenatal corticosteroids include: Systemic maternal infection Maternal chorioamnionitis
Drugs
Corticosteroids encourage the development of the lungs in a premature fetus before birth, and are administered when the premature fetus is expected to be delivered within 24 to 48 hours. The period of optimal benefit begins 24 hours after administration and lasts 7 days. In some parts of the world, antenatal steroids are used at up to 36 weeks of pregnancy. The time between administration of steroids and delivery may alter the effectiveness of the steroids.
Choice of steroid
Common corticosteroids include dexamethasone and betamethasone. Dexamethasone is often recommend over the latter due to its increased efficacy and safety, wide availability, and low cost, while betamethasone is better at preventing the softening of the brain in premature fetuses. Both drugs share certain commonalities, including the ability to traverse the placenta, as well as a very similar molecular structure. In fact, the two steroids are identical save for a single additional methyl group on betamethasone. Although betamethasone has an increased half-life, there is no significant evidence indicating that one might be better than the other. Literature on the subject is limited and inconsistent. A Cochrane review (2022) found that it was unclear if there were significant differences, while other studies determined that betamethasone results in improved longer term outcomes.