ABSTRACT
Lifestyle changes of women in developed countries during the second half of the 20th century mean that the age at which childbirth is desired has increased. Involuntary infertility and naturally reduced fecundity of advanced age have required new treatments1. As a result of higher maternal age and the use of poorly monitored ovulation induction and assisted reproductive technologies (ART), the incidence of twin and multiple births increased in the United States from 1971 to 1997 by epidemic proportions, with the immediate consequence of an increase in the numbers of infants born at < 33 weeks (1.7% of singletons, 13.9% of twins and 41.2% of triplets)2. Likewise, twin births have increased in most developed countries since the late 1970s3. Several studies indicate that twin infants originating after in vitro fertilization (IVF) have an even greater tendency to prematurity than naturally conceived twins4.
