Twin pregnancy. Ultrasonographically observed changes in fetal presentation.

The changes in fetal presentation throughout pregnancy were observed ultrasonographically in 332 sets of twins. Seventy-eight percent of the leading twins were vertex at 26-30 weeks' gestational age, 75% at 31-34 weeks and 81% at 35-38 weeks. The incidence of nonvertex presentation for either twin was 73.0%, 64.5% and 59.5% at the same gestational ages. The results are not significantly different from those on concordant twins delivered at the same gestations. Thus, one can counsel parents of twins at all gestational ages in regard to the potential for malpresentation.