Premature closure of the ductus arteriosus: variable response among monozygotic twins after in utero exposure to indomethacin.

Exposure of the fetus to indomethacin by administration of the drug to the mother may cause many side effects, including premature closure of the ductus arteriosus. Hypoxia is a predisposing factor for premature ductal closure and often occurs after maternal indomethacin therapy. We present two sets of monozygotic twins with twin-to-twin transfusion, where in utero ductal closure occurred in the donor twin while the recipient twin appeared unaffected. This selective closure of the ductus arteriosus suggests that the affected twin was predisposed to hypoxia and thus was more susceptible to ductal closure in response to indomethacin exposure.