Bangladesh Institute of Ultrasound in Medicine & Research, University of Science & Technology Chittagong
AIUM, ACR, ACOG, BSUM, etc. national organizations on ultrasonography have developed practice guidelines for performance of an antepartum obstetric ultrasound examination. Every guideline has emphasized on detection of embryonic or fetal number. There is no question that, with a careful examination, the true number of embryos can be accurately determined in the first trimester. In 1998, Doubilet & Benson analyzed 325 pregnancies with multiple gestations and found that 14％ had undercount in previous examinations. The examiner may underestimate the number of developing gestations and embryos if a thorough evaluation of the gestational sac is not made for all embryos. Small gestational sac can be missed or yolk sac may not be visualized before 5.5 weeks of gestational age. In 1986, Jeanty & Romero sonographically detected 7.6％ multiple pregnancies in early pregnancy whereas multiple pregnancy deliveries were 1.3％ only. It indicates high percentage of vanishing twin. Refraction artifacts, retrosac hematoma, inevitable abortion, or a curved single sac giving impression of double sacs are main causes of vanishing twin. Why fetal number is so important? It is due to patient management. Multiple pregnancy needs counseling to the mother and the family. Moreover there are problems specific to multiple pregnancy. There are anomalies specific to multiple pregnancy, which detection and management is very important for favorable outcome.