Do we use too much antenatal betamethasone?

To review and rationalize the liberal use of antenatal betamethasone in the setting of threatened preterm birth.

A retrospective review was performed using the charts of all patients at Ste-Justine Hospital, Montreal QC, who received antenatal betamethasone between 01 April 1997 and 31 March 1998. Initial treatment consisted of 2 doses of 12 mg IM given 24 hours apart. Repeat doses of 12 mg weekly were administered at the discretion of the treating physician. Optimal antenatal betamethasone therapy was defined as delivery within 1 week of initial treatment, prior to 34 weeks. Aside from number and timing of doses, other factors analyzed included: gestational age at admission and delivery, diagnosis associated with threatened preterm birth (PTB), number of hospital admissions, and delay between re-admission and delivery.

Of the 334 patients identified, 82 (25%) received optimal treatment. Of the remaining 252 patients, 204 (81%) received repeat doses. In the repeat dose group, 112 (55%) women delivered after 34 weeks, while 70 of the 92 remaining patients were hospitalized until delivery. The other 22 patients who received serial doses were discharged at least once prior to delivery; of these patients, 8 were re-admitted more than 24 hours pre-delivery (i.e., adequate time for re-treatment), while 14 were not, but only 6 of these were delivered urgently. Thus, a maximum of 60 patients (25% of repeat doses) could potentially have benefited from this approach. Of the 48 patients not receiving repeat doses, 37 (77%) delivered after 34 weeks. Five remained hospitalized, and 6 were discharged prior to delivery and re-admitted (2 patients > 24 hr and 4 patients < 24 hr from delivery). This represented a potential underutilization of betamethasone by 3% (11/334) of the patients, but only 1.8% (6/334) were of less than 32 weeks' gestation.

This study demonstrated the difficulty in predicting which of the patients presenting with threatened preterm birth would actually go on to deliver during the window of benefit of antenatal betamethasone therapy. Our desire to permit all premature fetuses to profit from the positive effects of this therapy must be balanced by a reserve in exposing too many to too much. Use of antenatal betamethasone in our unit has significantly decreased since this review.