THE EFFECT OF GESTATIONAL-AGE AND FETAL INDOMETHACIN LEVELS ON THE INCIDENCE OF CONSTRICTION OF THE FETAL DUCTUS-ARTERIOSUS

Objective: To determine the effects of gestational age and fetal serum indomethacin levels on constriction of the ductus arteriosus after ma ternal indomethacin administration. Methods: Twenty-five pregnant Rh-s ensitized patients were given a 50-mg oral dose of indomethacin 6 hour s before fetal serum indomethacin levels were determined at the time o f 50 diagnostic or therapeutic funipunctures. The ductus arteriosus wa s evaluated with Doppler ultrasound immediately before 40 of the proce dures. Constriction of the ductus arteriosus was defined as a peak dia stolic flow greater than 35 cm/second. Least-squares regression and mu ltiple regression were used for statistical analysis. Results: The pea k diastolic velocity of the fetal ductus arteriosus after maternal ind omethacin ingestion was constant at 25 cm/second before 27 weeks, incr eased between 27-30 weeks to a mean of 39 cm/second, and was stable th ereafter (R2 = 0.35; P < .05). There was no significant correlation be tween constriction of the ductus and fetal serum indomethacin levels ( P = .17). Conclusions: The constrictive effect of maternal indomethaci n ingestion on the fetal ductus arteriosus begins as early as 27 weeks ' gestation. Constriction of the ductus arteriosus is independent of f etal serum indomethacin levels.