A term delivery occurs on or after 37 weeks gestation. Any delivery prior is considered “preterm” and those between 34 weeks, 0 days and 36 weeks, 6 days are often referred to as “late preterm.” The standard of care has been to recommend antenatal glucocorticoids (typically, betamethasone 12.5mg IM q24 hours x 2 doses) to women who are anticipated to deliver a viable infant prior to 34 weeks, 0 days gestation. However, this regimen has not been routinely given to women expected to deliver in the late preterm window. This includes women suspected to be developing preterm labor and women with any condition requiring an iatrogenic preterm delivery. For example, I recently developed preeclampsia at 36 weeks gestation and required an early delivery. My OB and I never discussed betamethasone, because I was in the late preterm window.
I have also been the OB for many patients in this same situation and I likewise have not discussed glucocorticoids with those women expected to deliver a late preterm infant. More than one medical student has asked about this. They have noticed that we define all infants born prior to 37 weeks gestation as “preterm,” but only give glucocorticoids to those expected to deliver prior to 34 weeks gestation. They ask, “Wouldn’t all preterm infants benefit?” My short answer has always been that the data from prior trials supported glucocorticoids up until 34 weeks gestation, but the benefit for late preterm infants remained unclear. The obstetric community has been awaiting the results from the Antenatal Late Preterm Study, which is published in this week’s NEJM.
In this multicenter randomized controlled trial, 2831 women with singleton pregnancies and at risk for a late preterm delivery were randomized to receive antenatal glucocorticoids (betamethasone x 2 doses) or placebo. The primary outcome was a composite of newborn complications, largely related to the need for respiratory support. The primary outcome occurred less often in the treatment group than in the placebo group, but newborns in the treatment group were more likely to have hypoglycemia shortly after birth. The authors concluded that administration of betamethasone to women at risk for a late preterm delivery significantly reduced the rate of newborn respiratory complications.
These results provide support for extending the current guidelines such that women at risk for any preterm delivery receive glucocorticoids. In fact, the American College of Obstetricians & Gyncologists (ACOG) released an updated Practice Advisory on April 4th. They now say, “administration of betamethasone may be considered in women with a singleton pregnancy between 34 0/7 and 36 6/7 weeks gestation at imminent risk of preterm birth within 7 days.” However, some experts suggest that guideline changes should reflect caution and should not necessarily be extended all the way up to a term gestational age, where the benefits of respiratory complications are likely to be less evident and the risk of hypoglycemia remains. The decision of whether or not to give betamethasone will ultimately depend on clinical judgement. Most OBs will probably employ a cautious discussion with each patient, considering the exact gestational age, likelihood of a late preterm delivery, and comorbidities of the individual patient (particularly diabetes) before moving on to a blanket change in practice.