Comparison between oral and intramuscular dexamethasone in suppressing unconjugated estriol levels during the third trimester

Abstract

Objectives: Unconjugated estriol production depends on fetal adrenal androgen precursors. Fetal exposure to exogenous glucocorticoids results in adrenal suppression with a subsequent decrease in maternal serum unconjugated estriol levels. We compared the efficacy between oral and intramuscular dexamethasone in maternal serum unconjugated estriol suppression at 48 hours after the initial dose among women at risk for preterm delivery.

Study design: Twenty-four gravidas at risk for preterm delivery were randomized to receive either 6 mg intramuscular or 8 mg oral dexamethasone every 12 hours for a total of 4 doses. Blood samples (9 mL) were obtained before the initial dexamethasone administration and again after the fourth dose. Serum was separated and frozen at -70 degreesC and subsequently underwent batch analysis. Unconjugated estriol levels were determined by radioimmunoassay with intra-assay and interassay coefficients of variation of 7.9% and 5.5%, respectively. All values are reported as mean +/- SD. The primary statistical analysis was a t test, with P <.05 considered significant.

Results: At the time of dexamethasone administration, gestational ages in both groups were similar. Predexamethasone and postdexamethasone unconjugated estriol levels were also similar between the intramuscular and oral groups (5.39 +/- 3.99 vs 1.80 +/- 2.49 ng/mL and 6.05 +/- 3.00 vs 1.61 +/- 1.03 ng/mL, respectively, P >.05). No difference in percent decrease in unconjugated estriol levels was found between the intramuscular (0.67 +/- 0.24) and oral (0.65 +/- 0.39) groups.

Conclusion: Oral dexamethasone (8 mg) produces similar maternal serum unconjugated estriol suppression compared with intramuscular dexamethasone (6 mg) when evaluated 48 hours after administration.