The effect of indomethacin tocolysis on fetal ductus arteriosus constriction with advancing gestational age.

OBJECTIVE: Our purpose was to determine whether continuing exposure to indomethacin tocolysis is associated with an increased incidence of constriction of the human fetal ductus arteriosus with advancing gestational age.

STUDY DESIGN: Fetal echocardiograms were reviewed in 61 cases in which the pregnant women were treated for preterm labor with indomethacin (25 mg orally every 6 hours). Density function analysis and regression analysis were used to assess the effect of indomethacin tocolysis on ductal constriction with advancing gestational age.

RESULTS: A total of 193 fetal echocardiograms were obtained for 72 fetuses. Ductal constriction developed in 50% of the fetuses ranging from 24.7 to 35.0 weeks' gestation. Fetuses with indomethacin-induced ductal constriction demonstrated a greater increase in systolic flow velocities with advancing gestational age compared with the nonconstricted group (p < 0.05). Constriction was detected at a mean gestational age of 30.9 +/- 2.3 weeks at an average of 5.1 +/- 6.0 days after initiation of therapy. Ductal constriction occurred by 31 weeks' gestation in 70% of the affected fetuses. After discontinuation of indomethacin therapy, all follow-up echocardiograms demonstrated a return to nonconstricted ductal flow velocities. No significant adverse neonatal outcomes were attributed to indomethacin use.

CONCLUSIONS: A dramatic yet reversible increase in the incidence of indomethacin-induced ductal constriction occurs at 31 weeks' gestation. However, ductal constriction can occur at any gestational age. With indomethacin tocolysis, weekly fetal echocardiography is warranted for the duration of therapy.