The objective of this paper is to study the possible additive effect of cor
ticosteroids to the known effect of indomethacin on potency of the human du
ctus arteriosus. Systolic and diastolic blood flow of the fetal ductus arte
riosus was measured by echo Doppler at 26-32 weeks of gestation. Four group
s of patients were studied according to the treatment they have received: g
roup A (exposure to indomethacin and betamethasone); group B (indomethacin
alone); group C (betamethasone); and group D (controls). Children in whom d
uctal constriction was noted in utero were followed by repeat cardiac echo
Doppler examinations at the age of 1 to 2 years. In group A (indomethacin a
nd betamethasone) fetal ductal constriction was significantly higher (p = 0
.02) and occurred in 1 1 out of 15 fetuses (73.3%), compared with 5 out of
14 (37.2%) of the fetuses in group B (indomethacin alone). In group C (beta
methasone) and D fetuses (no treatment), no significant ductal constriction
was observed. Pathological tricuspid regurgitation and right ventricular d
ilation were found more frequently in fetuses from group A. No long-term se
quella was noted in the infants in whom ductal constriction had been noted
in utero. Corticosteroids and indomethacin have a synergistic effect on the
frequency and severity of fetal ductus arteriosus constriction. In short-t
erm treatment this effect is transient, and has no deleterious effects bn f
etal and neonatal cardiac function.