The Effect of Gestational Age and Fetal Indomethacin Levels on the Incidence of Constriction of the Fetal Ductus Arteriosus

Abstract

Objective: To determine the effects of gestational age and fetal serum indomethacin levels on constriction of the ductus arteriosus after maternal indomethacin administration. Methods: Twenty-five pregnant Rh-sensitized patients were given a 50-mg oral dose of indomethacin 6 hours before fetal serum indomethacin levels were determined at the time of 50 diagnostic or therapeutic funipunctures. The ductus arteriosus was evaluated with Doppler ultrasound immediately before 40 of the procedures. Constriction of the ductus arteriosus was defined as a peak diastolic flow greater than 35 cm/second. Least-squares regression and multiple regression were used for statistical analysis. Results: The peak diastolic velocity of the fetal ductus arteriosus after maternal indomethacin ingestion was constant at 25 cm/second before 27 weeks, increased between 27-30 weeks to a mean of 39 cm/second, and was stable thereafter (R2 = 0.35;P< .05). There was no significant correlation between constriction of the ductus and fetal serum indomethacin levels (P= .17). Conclusions: The constrictive effect of maternal indomethacin ingestion on the fetal ductus arteriosus begins as early as 27 weeks' gestation. Constriction of the ductus arteriosus is independent of fetal serum indomethacin levels.(Obstet Gynecol 1993;82:500-3)