ABSTRACT
The early diagnosis of chorionicity and amnionicity in multiple pregnancy forms the basis of the modern perinatal approach. Without knowing these basic parameters, it is virtually impossible to manage multifetal pregnancy adequately. At the outset it must be emphasized that the determination of chorionicity and amnionicity, as well as dating the gestation, are not only most accurate but also easiest to perform in the first trimester. An additional advantage of scanning the pregnancy at these early stages is that, owing to a generous amount of amniotic fluid, numerous anomalies, such as those of the body contours, brain, limbs, etc., visible at this stage of the pregnancy can be detected. Likewise, natural spontaneous reductions, which occur commonly in multifetal gestations, can easily be documented. Of equal importance, early diagnosis of multifetal pregnancies allows the perinatologist or the obstetrician to counsel the patient properly for fetal as well as maternal risks. Routine sonography during the first trimester of singleton pregnancies, once a matter of great debate, is slowly becoming recognized worldwide as being of great importance. In multifetal pregnancies, on the other hand, an early approach to sonographic evaluation is absolutely essential. A short 2-3-min ultrasound examination performed by an individual with experience, and using a modern machine, during the first trimester can reliably assess chorionicity and amnionicity. In stark contrast, the same task performed during or beyond the second trimester may be an extremely labor-intensive and tedious process, at the end of which even experienced sonologists and sonographers will frequently be wrong in correctly assigning chorionicity and amnionicity.
