Maternal Fetal Medicine / Department of Obstetrics and Gynaecology, The Chinese University of Hong Kong
The advances in ultrasound technology have enabled us not only in measuring nuchal translucency（NT）for Down syndrome screening, but also in detail examination of the fetal morphology during the first trimester. Approximately 50％of major fetal malformations can be diagnosed when the fetal crown-rump length is just 5-8cm long. The detection rated of some major malformations such as anencephaly, holoporsencephaly, and abdominal defects approach 100％．Although some of the fetal malformations will not be revealed until the second trimester, first trimester morphological screening has several advantages:（1）it allows an earlier diagnosis of fetal structural abnormalities, which may need further genetic investigations which may take time;（2）when compared to late intervention, earlier intervention such as termination of pregnancy for lethal fetal condition may be beneficial in term of physical and psychological health of the mothers;（3）it may reveal some important markers（e.g. tricuspid regurgitation, reversed a-wave in ductus venosus, reduced intra-cranial translucency）that are indications for subsequent second trimester morphology scanning;（4）early occurrence of malformation may also be an indicator of prognosis e.g. diaphragmatic hernia diagnosed in the first trimester has worse prognosis compared to those diagnosed later. In addition, in comparison to those of second trimester, the skill and time required for first trimester screening is less demanding so that it is not difficult to incorporate morphology screening during a NT scan. In future, measurement of uterine artery blood flow may be included in the first trimester scan as part of the screening program of pre-eclampsia. The combined ultrasound and biochemical（PlGF）screening test may achieve a detection rate of 90％for early-onset pre-eclampsia.