Prolonged morphine exposure in utero causes fetal and placental vasoconstriction: a case report.

Vasoconstriction was observed in the fetal middle cerebral and umbilical arteries by Doppler assessment at 27 weeks gestation in a patient requiring continuous morphine infusion for pain control. Fetal heart tracings were also concerning. Fetal status improved after a change to fentanyl infusion, a shorter acting opioid. Caution is recommended when long-term chronic narcotic infusion is used in pregnancy.