No Difference in Morbidity in Twins Born at 37, 38 Weeks.

BEAVER CREEK, COLO. -- Twins delivered at 37 weeks' gestation fare as well as those delivered at 38 weeks, according to a study of 173 sets of twins.

Delivery sometime between 37 and 38 weeks appears optimal with twin gestations, Dr. David F. Lewis maintained at a perinatal conference sponsored by the University of California, Irvine.

Although his study found no significant difference in morbidity between 37 weeks and 38 weeks, population studies that can detect extremely small differences have found evidence that fetal outcomes begin to worsen sometime after 37 weeks.

Two large population-based studies have indicated that fetal and perinatal mortality in twins decreases with every week up to 37 weeks but then it begins to rise again, said Dr. Lewis of the University of Kentucky, Lexington.

Still, Dr. Lewis said he did not think the evidence showed a dramatic enough risk after 37 weeks that he would recommend patients be routinely induced without a specific indication at 37 weeks.

Nevertheless, if there is an indication, delivery should be considered, he said.

Moreover, it might be wise for obstetricians to start thinking about antenatal testing beginning at 38 weeks, Dr. Lewis advised.