Take Care to Avoid Misconceptions and Myths About Multifetal Pregnancies.

MAUI, HAWAII -- The growing incidence of multifetal gestation has given rise to several myths and misconceptions, Dr. Manuel Porto said at a conference on ob.gyn. ultrasound sponsored by the University of California, Irvine.

Don't be fooled into thinking that twins conceived through assisted reproductive technology (ART) necessarily are dichorionic, dizygotic twins, said Dr. Porto, who is director of maternal-fetal medicine at the university.

At least 1% of multifetal gestations conceived after ovulation induction will be monozygotic twins. Among 218 ART pregnancies studied at the University of Iowa, Iowa City, 10% were twin gestations, nearly one-third of which were monozygotic, he noted. Higher-order multiple gestations also may be monozygotic.

Indeed, there is evidence that some ART procedures such as intracyto-plasmic sperm injection and assisted hatching may increase the chance of zygotes splitting Dr. Porto added at the meeting, which was also sponsored by Long Beach Memorial Medical Center.

Another misconception about multifetal gestations among patients and some health care providers is that monozygotic twins share one amniotic sac. Only about 1%-2% of monochorionic, monozygotic twins will be monoamnionic, he said. Most are in individual sacs separated by a thin, visible ...