ABNORMAL WAVEFORMS IN THE DUCTUS ARTERIOSUS

IUGR

Ductus arteriosus velocity does not appear to be useful in the fetus with IUGR.

• In a study of 20 IUGR fetuses (1).
• Velocity in the ductus arteriosus was normal in all fetuses.
• PI in the umbilical artery in 16 fetuses.
• Absent or reverse flow during diastole in the umbilical artery in nine cases.

Increases placental vascular resistance does therefore not appear to influence blood flow in the fetal ductus arteriosus.

EFFECTS OF INDOMETHACIN THERAPY

Indomethacin, a prostoglandin synthetase inhibitor, is used in the management of polyhydramnios and preterm labor. It causes constriction of the ductus arteriosus and tricuspid insufficiency in utero (2). This may result in increased pulmonary blood flow, neonatal pulmonary hypertension, shunting of blood through the foramen ovale and persistent fetal circulation after birth. 30-40% of exposed fetuses develop ductal constriction (7-9% are severe).

Classification of ductal constriction (1):

• Mild constriction - Peak velocity of the ductus arteriosus increases while end-diastolic velocity remains constant.
• Moderate constriction - Peak and end diastolic velocities increase above baseline values in the ductus. There is no tricuspid incompetence.
• Severe constriction - Tricuspid incompetence occurs. This usually occurs with end-diastolic velocities greater than 100-120cm/sec.

REFERENCES

1. Mari G, Adrignolo A, Deter RL et.al. Flow velocity waveforms of the ductus arteriosus in appropriate and small-for-gestational-age fetuses. Proceedings, 6th Congress of the International Perinatal Doppler Society. Rome. September 1993.
2. Mari G, Moise KJ, Deter RL et.al. Doppler assessment of the pulsatility index of the middle cerebral artery during constriction of the fetal ductus arteriosus following indomethacin therapy. Am J Obstet Gynecol 1989;161:1528-1531.