Abstract
Objective: To estimate the effect of single and recurrent doses of antenatal corticosteroids on fetal bone metabolism. Methods: This was a secondary analysis of a cohort of pregnant women from a previously reported randomized, placebo-controlled, multicenter trial of women at risk for preterm delivery who received weekly courses of betamethasone (active) or placebo after an initial course of corticosteroids. Umbilical cord serum levels of carboxy-terminal carboxy-terminal propeptide of type I procollagen and cross-linked carboxy-terminal telopeptide of type I procollagen were measured to assess the rate of fetal bone formation and resorption, respectively. Analysis was stratified according to number of repeat antenatal study courses of betamethasone or placebo (one to three compared with at least four courses, not including the initial course). Results: Of the 251 umbilical cord serum samples, the median serum carboxy-terminal telopeptide of type I procollagen levels, but not carboxy-terminal propeptide of type I procollagen levels, was significantly lower with repeat betamethasone exposure (55.0 compared with 57.9 micrograms/L, P=.01). In the fetuses exposed to at least four repeat study courses, there was a significant decrease in median carboxy-terminal telopeptide of type-I procollagen levels between repeat betamethasone exposure and placebo (53.4 compared with 58.6 micrograms/L, respectively, P=.04), but there was no difference between groups in the fetuses exposed to 1-3 repeat study courses (57.4 compared with 56.7 micrograms/L, respectively, P=.29). Conclusion: Levels of umbilical cord serum markers of bone resorption but not formation are reduced in fetuses exposed to repeat courses of antenatal betamethasone. Up to four courses of antenatal betamethasone do not seem to affect fetal bone metabolism. Level of evidence: II.